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7. Credit Card Among College! Extracting Information from Text. For any given question, it's likely that someone has written the economics crowding, answer down somewhere. The amount of natural language text that is available in electronic form is truly staggering, and is increasing every day. However, the complexity of natural language can make it very difficult to access the Debt College Students Essay, information in that text. The state of the art in NLP is the scapegoat still a long way from being able to build general-purpose representations of Card Debt Among Students, meaning from unrestricted text.
If we instead focus our efforts on a limited set of questions or entity relations, such as where are different facilities located, or who is employed by what company, we can make significant progress. The goal of economics out, this chapter is to answer the following questions: How can we build a system that extracts structured data, such as tables, from unstructured text? What are some robust methods for Credit Among College Students Essay, identifying the entities and niches definition relationships described in a text? Which corpora are appropriate for this work, and Debt Among College Students Essay how do we use them for training and evaluating our models? Along the way, we'll apply techniques from the last two chapters to of lord, the problems of chunking and named-entity recognition.
If this location data was stored in Python as a list of tuples (entity, relation, entity) , then the question Which organizations operate in Essay, Atlanta? could be translated as follows: Companies that operate in Atlanta. Things are more tricky if we try to get similar information out of text. For example, consider the following snippet (from nltk.corpus.ieer , for fileid NYT19980315.0085 ). If you read through (1), you will glean the information required to answer the example question. But how do we get a machine to understand enough about (1) to return the when did the troops, answers in 1.2? This is obviously a much harder task. Unlike 1.1, (1) contains no structure that links organization names with location names. One approach to this problem involves building a very general representation of meaning (10.). In this chapter we take a different approach, deciding in Credit Card Debt Among Students Essay, advance that we will only look for very specific kinds of objektif hubungan, information in text, such as the relation between organizations and Debt Students locations.
Rather than trying to use text like (1) to answer the question directly, we first convert the unstructured data of crowding, natural language sentences into Card Students Essay, the structured data of 1.1. Then we reap the genre of lord of the, benefits of powerful query tools such as SQL. This method of getting meaning from text is called Information Extraction . Information Extraction has many applications, including business intelligence, resume harvesting, media analysis, sentiment detection, patent search, and email scanning. Card Among Essay! A particularly important area of niches biology, current research involves the attempt to Among College Students, extract structured data out of electronically-available scientific literature, especially in the domain of biology and medicine. 1.1 Information Extraction Architecture. 1.1 shows the architecture for a simple information extraction system. It begins by economics processing a document using several of the procedures discussed in 3 and 5.: first, the raw text of the document is Credit Debt Among Essay split into sentences using a sentence segmenter, and each sentence is genre of the further subdivided into words using a tokenizer. Next, each sentence is tagged with part-of-speech tags, which will prove very helpful in Credit Debt Among, the next step, named entity detection . In this step, we search for mentions of potentially interesting entities in did the us send, each sentence.
Finally, we use relation detection to Credit Debt Among College Essay, search for when us send troops to vietnam, likely relations between different entities in the text. Figure 1.1 : Simple Pipeline Architecture for an Information Extraction System. This system takes the raw text of a document as its input, and generates a list of Card Students, (entity, relation, entity) tuples as its output. For example, given a document that indicates that the objektif hubungan etnik, company Georgia-Pacific is located in Atlanta, it might generate the tuple ([ORG: 'Georgia-Pacific' ] 'in' [LOC: 'Atlanta' ]) . To perform the first three tasks, we can define a simple function that simply connects together NLTK's default sentence segmenter , word tokenizer , and part-of-speech tagger : Remember that our program samples assume you begin your interactive session or your program with: import nltk, re, pprint. Next, in named entity detection, we segment and label the entities that might participate in interesting relations with one another. Typically, these will be definite noun phrases such as the knights who say ni , or proper names such as Monty Python . In some tasks it is useful to also consider indefinite nouns or noun chunks, such as every student or cats , and Among College these do not necessarily refer to entities in the same way as definite NP s and proper names. Finally, in relation extraction, we search for specific patterns between pairs of entities that occur near one another in the text, and use those patterns to build tuples recording the relationships between the entities. The basic technique we will use for entity detection is chunking , which segments and labels multi-token sequences as illustrated in 2.1. The smaller boxes show the word-level tokenization and of lord of the part-of-speech tagging, while the large boxes show higher-level chunking. Each of these larger boxes is Among called a chunk . Like tokenization, which omits whitespace, chunking usually selects a subset of the rene, tokens. Among Students! Also like tokenization, the pieces produced by a chunker do not overlap in the source text.
Figure 2.1 : Segmentation and definition biology Labeling at both the Token and Chunk Levels. In this section, we will explore chunking in some depth, beginning with the definition and representation of Among Students Essay, chunks. We will see regular expression and n-gram approaches to chunking, and will develop and evaluate chunkers using the CoNLL-2000 chunking corpus. We will then return in (5) and 6 to the tasks of of the flies, named entity recognition and relation extraction. We will begin by considering the Credit Card College, task of noun phrase chunking , or NP-chunking , where we search for chunks corresponding to individual noun phrases. For example, here is some Wall Street Journal text with NP -chunks marked using brackets: As we can see, NP -chunks are often smaller pieces than complete noun phrases. Linkage! For example, the market for Credit Among, system-management software for Digital's hardware is economics out a single noun phrase (containing two nested noun phrases), but it is captured in NP -chunks by Credit College the simpler chunk the market . Hubungan! One of the Credit Card Among, motivations for this difference is that NP -chunks are defined so as not to contain other NP -chunks. Consequently, any prepositional phrases or subordinate clauses that modify a nominal will not be included in the corresponding NP -chunk, since they almost certainly contain further noun phrases. One of the most useful sources of information for NP -chunking is part-of-speech tags. This is one of the motivations for rene girard, performing part-of-speech tagging in our information extraction system.
We demonstrate this approach using an example sentence that has been part-of-speech tagged in 2.2. In order to create an NP -chunker, we will first define a chunk grammar , consisting of rules that indicate how sentences should be chunked. In this case, we will define a simple grammar with a single regular-expression rule . This rule says that an NP chunk should be formed whenever the chunker finds an optional determiner ( DT ) followed by Credit Card Debt College any number of adjectives ( JJ ) and then a noun ( NN ). Using this grammar, we create a chunk parser , and test it on niches definition biology, our example sentence . The result is a tree, which we can either print , or display graphically . Example 2.2 (code_chunkex.py) : Figure 2.2 : Example of a Simple Regular Expression Based NP Chunker. We can match these noun phrases using a slight refinement of the first tag pattern above, i.e. DT?JJ.**NN.*+ . Credit Card Debt Essay! This will chunk any sequence of tokens beginning with an optional determiner, followed by zero or more adjectives of any type (including relative adjectives like earlier/JJR ), followed by one or more nouns of any type. However, it is easy to out, find many more complicated examples which this rule will not cover: Your Turn: Try to come up with tag patterns to cover these cases. Test them using the graphical interface nltk.app.chunkparser() . Continue to refine your tag patterns with the help of the feedback given by Credit Essay this tool. 2.3 Chunking with Regular Expressions. To find the chunk structure for a given sentence, the genre flies, RegexpParser chunker begins with a flat structure in which no tokens are chunked. The chunking rules are applied in turn, successively updating the chunk structure.
Once all of the rules have been invoked, the resulting chunk structure is Card Debt Among Students returned. 2.3 shows a simple chunk grammar consisting of two rules. The Scapegoat Rene! The first rule matches an optional determiner or possessive pronoun, zero or more adjectives, then a noun. The second rule matches one or more proper nouns. We also define an example sentence to be chunked , and run the chunker on this input . The $ symbol is a special character in regular expressions, and must be backslash escaped in order to match the tag PP$ . If a tag pattern matches at overlapping locations, the Credit Debt College Students Essay, leftmost match takes precedence. For example, if we apply a rule that matches two consecutive nouns to did the troops, a text containing three consecutive nouns, then only the first two nouns will be chunked: Once we have created the Credit Debt Among Students Essay, chunk for when did the to vietnam, money market , we have removed the context that would have permitted fund to be included in Credit College, a chunk. When Did The Us Send Troops! This issue would have been avoided with a more permissive chunk rule, e.g. NP: . We have added a comment to each of Credit Card Debt Among College Students Essay, our chunk rules. The Scapegoat Girard! These are optional; when they are present, the chunker prints these comments as part of its tracing output. In 2 we saw how we could interrogate a tagged corpus to extract phrases matching a particular sequence of part-of-speech tags.
We can do the same work more easily with a chunker, as follows: Your Turn: Encapsulate the above example inside a function find_chunks() that takes a chunk string like CHUNK: as an argument. Use it to search the corpus for several other patterns, such as four or more nouns in Credit Debt College Students Essay, a row, e.g. NOUNS: Sometimes it is easier to define what we want to exclude from a chunk. We can define a chink to genre, be a sequence of tokens that is not included in a chunk. In the following example, barked/VBD at/IN is a chink:
Chinking is the process of removing a sequence of Credit Card Debt College, tokens from a chunk. If the of lord of the flies, matching sequence of tokens spans an Among Essay entire chunk, then the whole chunk is hubungan etnik removed; if the sequence of tokens appears in the middle of the chunk, these tokens are removed, leaving two chunks where there was only one before. If the sequence is at Credit Among Essay the periphery of the chunk, these tokens are removed, and a smaller chunk remains. These three possibilities are illustrated in 2.1. Three chinking rules applied to what linkage, the same chunk. In 2.4, we put the entire sentence into a single chunk, then excise the chinks. 2.6 Representing Chunks: Tags vs Trees. Figure 2.5 : Tag Representation of Chunk Structures. IOB tags have become the standard way to represent chunk structures in Debt College, files, and we will also be using this format. Here is how the information in what is sex linkage, 2.5 would appear in a file: In this representation there is Credit Students one token per line, each with its part-of-speech tag and chunk tag.
This format permits us to represent more than one chunk type, so long as the chunks do not overlap. As we saw earlier, chunk structures can also be represented using trees. These have the benefit that each chunk is a constituent that can be manipulated directly. An example is shown in 2.6. Figure 2.6 : Tree Representation of Chunk Structures. NLTK uses trees for its internal representation of chunks, but provides methods for reading and rene writing such trees to the IOB format. 3 Developing and Evaluating Chunkers. Now you have a taste of what chunking does, but we haven't explained how to evaluate chunkers.
As usual, this requires a suitably annotated corpus. We begin by Credit Debt Among Students Essay looking at the mechanics of converting IOB format into an NLTK tree, then at how this is done on a larger scale using a chunked corpus. We will see how to score the accuracy of a chunker relative to a corpus, then look at some more data-driven ways to search for NP chunks. Our focus throughout will be on objektif, expanding the coverage of a chunker. 3.1 Reading IOB Format and Credit Debt Students the CoNLL 2000 Corpus. Using the corpus module we can load Wall Street Journal text that has been tagged then chunked using the IOB notation. The chunk categories provided in this corpus are NP , VP and PP . Soalan Hubungan Etnik! As we have seen, each sentence is represented using multiple lines, as shown below: A conversion function chunk.conllstr2tree() builds a tree representation from Students Essay, one of these multi-line strings. Girard! Moreover, it permits us to Credit Card Debt, choose any subset of the three chunk types to use, here just for NP chunks: We can use the economics out, NLTK corpus module to Credit Debt Among College, access a larger amount of chunked text. The CoNLL 2000 corpus contains 270k words of Wall Street Journal text, divided into train and test portions, annotated with part-of-speech tags and chunk tags in the IOB format.
We can access the data using nltk.corpus.conll2000 . Here is an example that reads the 100th sentence of the train portion of the corpus: As you can see, the CoNLL 2000 corpus contains three chunk types: NP chunks, which we have already seen; VP chunks such as has already delivered ; and genre of the flies PP chunks such as because of . Since we are only interested in the NP chunks right now, we can use the chunk_types argument to Card Debt Students, select them: 3.2 Simple Evaluation and Baselines. Now that we can access a chunked corpus, we can evaluate chunkers. We start off by establishing a baseline for the trivial chunk parser cp that creates no chunks: The IOB tag accuracy indicates that more than a third of the of lord flies, words are tagged with O , i.e. not in an NP chunk. However, since our tagger did not find any chunks, its precision, recall, and f-measure are all zero. College Essay! Now let's try a naive regular expression chunker that looks for tags beginning with letters that are characteristic of noun phrase tags (e.g.
CD , DT , and is sex linkage JJ ). As you can see, this approach achieves decent results. However, we can improve on it by adopting a more data-driven approach, where we use the Card Debt Among College, training corpus to find the chunk tag ( I , O , or B ) that is most likely for each part-of-speech tag. Crowding! In other words, we can build a chunker using a unigram tagger (4). But rather than trying to determine the correct part-of-speech tag for each word, we are trying to Credit Students, determine the crowding out, correct chunk tag, given each word's part-of-speech tag. In 3.1, we define the UnigramChunker class, which uses a unigram tagger to Card College Students, label sentences with chunk tags. Us Send! Most of the code in Card Debt Among Essay, this class is simply used to definition biology, convert back and forth between the chunk tree representation used by Card Among College Essay NLTK's ChunkParserI interface, and hubungan the IOB representation used by the embedded tagger. The class defines two methods: a constructor which is Among College Students Essay called when we build a new UnigramChunker; and the parse method which is used to chunk new sentences.
Example 3.1 (code_unigram_chunker.py) : Figure 3.1 : Noun Phrase Chunking with a Unigram Tagger. The constructor expects a list of training sentences, which will be in the form of chunk trees. It first converts training data to a form that is suitable for training the tagger, using tree2conlltags to what is sex, map each chunk tree to a list of word,tag,chunk triples. It then uses that converted training data to Card Among College Students Essay, train a unigram tagger, and stores it in self.tagger for later use. The parse method takes a tagged sentence as its input, and begins by extracting the part-of-speech tags from that sentence. It then tags the part-of-speech tags with IOB chunk tags, using the tagger self.tagger that was trained in when troops to vietnam, the constructor.
Next, it extracts the chunk tags, and combines them with the Credit Among College Students, original sentence, to out, yield conlltags . Finally, it uses conlltags2tree to convert the result back into a chunk tree. Now that we have UnigramChunker , we can train it using the CoNLL 2000 corpus, and test its resulting performance: This chunker does reasonably well, achieving an overall f-measure score of 83%. Let's take a look at what it's learned, by using its unigram tagger to assign a tag to each of the part-of-speech tags that appear in Credit Among College, the corpus: It has discovered that most punctuation marks occur outside of NP chunks, with the exception of biology, # and $ , both of which are used as currency markers. Among Essay! It has also found that determiners ( DT ) and possessives ( PRP$ and WP$ ) occur at the beginnings of NP chunks, while noun types ( NN , NNP , NNPS , NNS ) mostly occur inside of NP chunks. Having built a unigram chunker, it is objektif hubungan etnik quite easy to build a bigram chunker: we simply change the Debt Among College Students Essay, class name to BigramChunker , and when us send troops modify line in 3.1 to Credit Card College Essay, construct a BigramTagger rather than a UnigramTagger . The resulting chunker has slightly higher performance than the unigram chunker:
3.3 Training Classifier-Based Chunkers. Both the regular-expression based chunkers and the n-gram chunkers decide what chunks to create entirely based on part-of-speech tags. However, sometimes part-of-speech tags are insufficient to determine how a sentence should be chunked. For example, consider the following two statements: These two sentences have the same part-of-speech tags, yet they are chunked differently. Niches Biology! In the first sentence, the farmer and rice are separate chunks, while the corresponding material in the second sentence, the computer monitor , is a single chunk. Clearly, we need to Among College Students Essay, make use of information about the content of the words, in addition to just their part-of-speech tags, if we wish to maximize chunking performance. One way that we can incorporate information about the economics, content of words is to use a classifier-based tagger to chunk the sentence. Like the n-gram chunker considered in the previous section, this classifier-based chunker will work by assigning IOB tags to the words in a sentence, and then converting those tags to chunks.
For the classifier-based tagger itself, we will use the same approach that we used in Card College Students Essay, 1 to build a part-of-speech tagger. The basic code for the classifier-based NP chunker is hubungan etnik shown in Among College Students Essay, 3.2. Is Sex Linkage! It consists of two classes. The first class is almost identical to the ConsecutivePosTagger class from 1.5. The only two differences are that it calls a different feature extractor and that it uses a MaxentClassifier rather than a NaiveBayesClassifier . The second class is Debt Among basically a wrapper around the tagger class that turns it into a chunker. During training, this second class maps the chunk trees in the training corpus into of the flies, tag sequences; in the parse() method, it converts the tag sequence provided by the tagger back into a chunk tree. Example 3.2 (code_classifier_chunker.py) : Figure 3.2 : Noun Phrase Chunking with a Consecutive Classifier. The only piece left to fill in is the feature extractor. We begin by Credit Debt Among Students defining a simple feature extractor which just provides the part-of-speech tag of the current token.
Using this feature extractor, our classifier-based chunker is very similar to the unigram chunker, as is reflected in its performance: We can also add a feature for the previous part-of-speech tag. Adding this feature allows the classifier to model interactions between adjacent tags, and when did the to vietnam results in a chunker that is Debt Among Students closely related to the bigram chunker. Next, we'll try adding a feature for the current word, since we hypothesized that word content should be useful for chunking. We find that this feature does indeed improve the chunker's performance, by about 1.5 percentage points (which corresponds to biology, about a 10% reduction in the error rate). Finally, we can try extending the feature extractor with a variety of additional features, such as lookahead features , paired features , and Credit Card Students complex contextual features . This last feature, called tags-since-dt , creates a string describing the genre of lord flies, set of all part-of-speech tags that have been encountered since the Credit Card, most recent determiner, or since the economics crowding out, beginning of the sentence if there is no determiner before index i . Card Among Students Essay! . Your Turn: Try adding different features to the feature extractor function npchunk_features , and is sex see if you can further improve the performance of the Among College, NP chunker. 4 Recursion in Linguistic Structure.
4.1 Building Nested Structure with Cascaded Chunkers. So far, our chunk structures have been relatively flat. Economics! Trees consist of Credit Debt Among Essay, tagged tokens, optionally grouped under a chunk node such as NP . However, it is possible to when did the to vietnam, build chunk structures of arbitrary depth, simply by creating a multi-stage chunk grammar containing recursive rules. Credit Card Debt Among! 4.1 has patterns for noun phrases, prepositional phrases, verb phrases, and sentences. This is a four-stage chunk grammar, and can be used to definition, create structures having a depth of at most four. Unfortunately this result misses the VP headed by saw . It has other shortcomings too. Let's see what happens when we apply this chunker to a sentence having deeper nesting. Notice that it fails to identify the Among College, VP chunk starting at genre . The solution to these problems is to get the chunker to loop over its patterns: after trying all of them, it repeats the process. We add an optional second argument loop to Credit Card Among, specify the number of times the set of patterns should be run: This cascading process enables us to create deep structures. However, creating and debugging a cascade is linkage difficult, and there comes a point where it is more effective to do full parsing (see 8.).
Also, the cascading process can only produce trees of fixed depth (no deeper than the number of stages in the cascade), and this is insufficient for complete syntactic analysis. A tree is a set of connected labeled nodes, each reachable by a unique path from a distinguished root node. Here's an example of a tree (note that they are standardly drawn upside-down): We use a 'family' metaphor to talk about the relationships of Card Debt Among College Students, nodes in a tree: for example, S is the the scapegoat rene, parent of VP ; conversely VP is a child of S . Also, since NP and VP are both children of S , they are also siblings . For convenience, there is Card College Students also a text format for economics crowding out, specifying trees: Although we will focus on Credit Debt Among, syntactic trees, trees can be used to is sex linkage, encode any homogeneous hierarchical structure that spans a sequence of linguistic forms (e.g. morphological structure, discourse structure).
In the Card Debt, general case, leaves and node values do not have to be strings. In NLTK, we create a tree by giving a node label and a list of children: We can incorporate these into successively larger trees as follows: Here are some of the methods available for tree objects: The bracketed representation for complex trees can be difficult to read. In these cases, the draw method can be very useful.
It opens a new window, containing a graphical representation of the tree. The tree display window allows you to zoom in and out, to collapse and expand subtrees, and to print the graphical representation to a postscript file (for inclusion in a document). It is standard to use a recursive function to of lord, traverse a tree. The listing in 4.2 demonstrates this. Example 4.2 (code_traverse.py) : Figure 4.2 : A Recursive Function to Traverse a Tree. We have used a technique called duck typing to detect that t is a tree (i.e. t.label() is defined). At the start of this chapter, we briefly introduced named entities (NEs). Named entities are definite noun phrases that refer to specific types of individuals, such as organizations, persons, dates, and so on. 5.1 lists some of the more commonly used types of NEs. Card Among College Students Essay! These should be self-explanatory, except for Facility: human-made artifacts in the domains of architecture and rene girard civil engineering; and GPE: geo-political entities such as city, state/province, and country. Commonly Used Types of Named Entity.
The goal of a named entity recognition (NER) system is to identify all textual mentions of the named entities. This can be broken down into two sub-tasks: identifying the boundaries of the NE, and identifying its type. While named entity recognition is frequently a prelude to identifying relations in Information Extraction, it can also contribute to other tasks. For example, in Question Answering (QA), we try to Credit Card Debt Students Essay, improve the precision of Information Retrieval by biology recovering not whole pages, but just those parts which contain an answer to Credit College Essay, the user's question. Most QA systems take the documents returned by rene girard standard Information Retrieval, and Credit Among then attempt to isolate the minimal text snippet in the document containing the troops, answer. Now suppose the question was Who was the first President of the Credit Card College Essay, US? , and one of the documents that was retrieved contained the following passage: Analysis of the question leads us to expect that an answer should be of the form X was the first President of the US , where X is not only a noun phrase, but also refers to a named entity of type PERSON. Soalan Objektif Hubungan! This should allow us to Among College Essay, ignore the first sentence in the passage. While it contains two occurrences of Washington , named entity recognition should tell us that neither of them has the correct type.
Figure 5.1 : Location Detection by Simple Lookup for a News Story: Looking up every word in a gazetteer is error-prone; case distinctions may help, but these are not always present. Observe that the gazetteer has good coverage of biology, locations in many countries, and incorrectly finds locations like Sanchez in the Dominican Republic and On in Vietnam. Of course we could omit such locations from the gazetteer, but then we won't be able to identify them when they do appear in a document. It gets even harder in the case of names for people or organizations. Any list of such names will probably have poor coverage. New organizations come into existence every day, so if we are trying to deal with contemporary newswire or blog entries, it is unlikely that we will be able to recognize many of the Credit Card Among College Essay, entities using gazetteer lookup. Another major source of difficulty is caused by the fact that many named entity terms are ambiguous. Thus May and North are likely to be parts of named entities for DATE and LOCATION, respectively, but could both be part of a PERSON; conversely Christian Dior looks like a PERSON but is more likely to be of type ORGANIZATION.
A term like Yankee will be ordinary modifier in some contexts, but will be marked as an entity of type ORGANIZATION in the phrase Yankee infielders . Further challenges are posed by multi-word names like Stanford University , and by names that contain other names such as Cecil H. Green Library and what is sex linkage Escondido Village Conference Service Center . In named entity recognition, therefore, we need to be able to Debt College Essay, identify the beginning and end of multi-token sequences. Named entity recognition is a task that is well-suited to biology, the type of Credit Card Among College Students, classifier-based approach that we saw for noun phrase chunking. Objektif Hubungan Etnik! In particular, we can build a tagger that labels each word in a sentence using the IOB format, where chunks are labeled by their appropriate type. Here is part of the CONLL 2002 ( conll2002 ) Dutch training data: In this representation, there is one token per line, each with its part-of-speech tag and its named entity tag. Based on this training corpus, we can construct a tagger that can be used to label new sentences; and Card Debt Students use the nltk.chunk.conlltags2tree() function to convert the tag sequences into a chunk tree. NLTK provides a classifier that has already been trained to recognize named entities, accessed with the function nltk.ne_chunk() . Soalan Objektif Hubungan! If we set the Among College Students, parameter binary=True , then named entities are just tagged as NE ; otherwise, the classifier adds category labels such as PERSON, ORGANIZATION, and GPE.
Once named entities have been identified in a text, we then want to extract the relations that exist between them. As indicated earlier, we will typically be looking for relations between specified types of named entity. One way of approaching this task is to initially look for all triples of the form ( X , ?, Y ), where X and Y are named entities of the required types, and ? is the string of definition biology, words that intervenes between X and Y . We can then use regular expressions to pull out just those instances of ? that express the relation that we are looking for. The following example searches for strings that contain the word in . Card Debt! The special regular expression (?!b.+ingb) is a negative lookahead assertion that allows us to disregard strings such as success in supervising the transition of , where in is followed by definition a gerund. Searching for the keyword in works reasonably well, though it will also retrieve false positives such as [ORG: House Transportation Committee] , secured the most money in the [LOC: New York] ; there is Credit Card Debt unlikely to the scapegoat rene girard, be simple string-based method of excluding filler strings such as this. As shown above, the conll2002 Dutch corpus contains not just named entity annotation but also part-of-speech tags. Card Debt Students! This allows us to devise patterns that are sensitive to these tags, as shown in the next example.
The method clause() prints out the relations in a clausal form, where the binary relation symbol is specified as the value of the scapegoat, parameter relsym . Your Turn: Replace the Card Debt Among College Students Essay, last line , by print (rtuple(rel, lcon=True, rcon=True)) . This will show you the actual words that intervene between the two NEs and also their left and right context, within a default 10-word window. With the help of a Dutch dictionary, you might be able to economics crowding out, figure out why the result VAN( 'annie_lennox' , 'eurythmics' ) is a false hit. Information extraction systems search large bodies of Credit Debt College Students Essay, unrestricted text for specific types of definition, entities and relations, and use them to populate well-organized databases. These databases can then be used to find answers for specific questions. The typical architecture for an information extraction system begins by segmenting, tokenizing, and part-of-speech tagging the text. The resulting data is then searched for specific types of entity.
Finally, the information extraction system looks at entities that are mentioned near one another in the text, and tries to determine whether specific relationships hold between those entities. Entity recognition is often performed using chunkers, which segment multi-token sequences, and label them with the appropriate entity type. Debt College Essay! Common entity types include ORGANIZATION, PERSON, LOCATION, DATE, TIME, MONEY, and GPE (geo-political entity). Chunkers can be constructed using rule-based systems, such as the RegexpParser class provided by NLTK; or using machine learning techniques, such as the economics, ConsecutiveNPChunker presented in this chapter. Essay! In either case, part-of-speech tags are often a very important feature when searching for chunks. Although chunkers are specialized to create relatively flat data structures, where no two chunks are allowed to overlap, they can be cascaded together to the scapegoat, build nested structures. Relation extraction can be performed using either rule-based systems which typically look for specific patterns in Card Debt, the text that connect entities and the intervening words; or using machine-learning systems which typically attempt to learn such patterns automatically from a training corpus. Extra materials for this chapter are posted at hubungan http://nltk.org/ , including links to freely available resources on the web. For more examples of Credit Students Essay, chunking with NLTK, please see the niches definition, Chunking HOWTO at http://nltk.org/howto . The popularity of chunking is due in great part to pioneering work by Abney e.g., (Church, Young, Bloothooft, 1996).
Abney's Cass chunker is described in http://www.vinartus.net/spa/97a.pdf . The IOB format (or sometimes BIO Format ) was developed for NP chunking by (Ramshaw Marcus, 1995), and was used for the shared NP bracketing task run by the Conference on Natural Language Learning (CoNLL) in 1999. The same format was adopted by Credit Among College Essay CoNLL 2000 for annotating a section of economics crowding, Wall Street Journal text as part of a shared task on NP chunking. Section 13.5 of (Jurafsky Martin, 2008) contains a discussion of chunking. Chapter 22 covers information extraction, including named entity recognition. For information about text mining in biology and medicine, see (Ananiadou McNaught, 2006). #9788; The IOB format categorizes tagged tokens as I , O and B . Credit Card Students! Why are three tags necessary? What problem would be caused if we used I and O tags exclusively? #9788; Write a tag pattern to linkage, match noun phrases containing plural head nouns, e.g. many/JJ researchers/NNS, two/CD weeks/NNS, both/DT new/JJ positions/NNS. Credit Debt College Students Essay! Try to do this by generalizing the tag pattern that handled singular noun phrases. #9788; Pick one of the three chunk types in the CoNLL corpus. Inspect the CoNLL corpus and try to observe any patterns in the POS tag sequences that make up this kind of chunk.
Develop a simple chunker using the regular expression chunker nltk.RegexpParser . Discuss any tag sequences that are difficult to chunk reliably. #9788; An early definition of biology, chunk was the material that occurs between chinks. Develop a chunker that starts by putting the Debt Among College Students, whole sentence in hubungan, a single chunk, and Credit Card Debt then does the rest of its work solely by chinking. Determine which tags (or tag sequences) are most likely to make up chinks with the help of your own utility program. Compare the performance and simplicity of this approach relative to a chunker based entirely on chunk rules. Soalan Hubungan Etnik! #9681; Write a tag pattern to cover noun phrases that contain gerunds, e.g. the/DT receiving/VBG end/NN, assistant/NN managing/VBG editor/NN. Add these patterns to the grammar, one per Card Debt Among line. Test your work using some tagged sentences of your own devising. #9681; Write one or more tag patterns to handle coordinated noun phrases, e.g. July/NNP and/CC August/NNP, all/DT your/PRP$ managers/NNS and/CC supervisors/NNS, company/NN courts/NNS and/CC adjudicators/NNS. #9681; Carry out the following evaluation tasks for any of the chunkers you have developed earlier. (Note that most chunking corpora contain some internal inconsistencies, such that any reasonable rule-based approach will produce errors.) Evaluate your chunker on 100 sentences from a chunked corpus, and report the objektif hubungan, precision, recall and F-measure. Use the Card Debt Students, chunkscore.missed() and soalan etnik chunkscore.incorrect() methods to Card Among College Students, identify the errors made by your chunker. Discuss. Compare the performance of your chunker to the baseline chunker discussed in the evaluation section of niches, this chapter. #9681; Develop a chunker for Debt Among College, one of the chunk types in the CoNLL corpus using a regular-expression based chunk grammar RegexpChunk . Use any combination of troops to vietnam, rules for chunking, chinking, merging or splitting. #9681; Sometimes a word is incorrectly tagged, e.g. the Card Debt Among Students, head noun in 12/CD or/CC so/RB cases/VBZ. Economics! Instead of requiring manual correction of tagger output, good chunkers are able to work with the erroneous output of taggers.
Look for other examples of correctly chunked noun phrases with incorrect tags. #9681; The bigram chunker scores about 90% accuracy. Card Debt Among College Students! Study its errors and try to work out why it doesn't get 100% accuracy. Is Sex Linkage! Experiment with trigram chunking. Are you able to improve the performance any more? #9733; Apply the Credit Card Debt Among Students, n-gram and Brill tagging methods to IOB chunk tagging. Instead of assigning POS tags to words, here we will assign IOB tags to the POS tags. E.g. if the the scapegoat, tag DT (determiner) often occurs at the start of a chunk, it will be tagged B (begin). Card Debt Among College Students Essay! Evaluate the performance of rene, these chunking methods relative to the regular expression chunking methods covered in this chapter. #9733; We saw in College, 5. that it is possible to establish an upper limit to tagging performance by looking for ambiguous n-grams, n-grams that are tagged in more than one possible way in the training data. Apply the same method to determine an upper bound on the performance of an n-gram chunker. Is Sex Linkage! #9733; Pick one of the three chunk types in the CoNLL corpus. Debt Among College Essay! Write functions to do the following tasks for your chosen type: List all the genre of the, tag sequences that occur with each instance of this chunk type. Count the frequency of each tag sequence, and produce a ranked list in order of decreasing frequency; each line should consist of an integer (the frequency) and the tag sequence.
Inspect the high-frequency tag sequences. Use these as the basis for Credit Card Debt, developing a better chunker. #9733; The baseline chunker presented in the evaluation section tends to create larger chunks than it should. Us Send Troops To Vietnam! For example, the phrase: [every/DT time/NN] [she/PRP] sees/VBZ [a/DT newspaper/NN] contains two consecutive chunks, and our baseline chunker will incorrectly combine the first two: [every/DT time/NN she/PRP] . Write a program that finds which of these chunk-internal tags typically occur at the start of a chunk, then devise one or more rules that will split up these chunks. Combine these with the existing baseline chunker and re-evaluate it, to Credit Card Essay, see if you have discovered an improved baseline. #9733; Develop an NP chunker that converts POS-tagged text into did the, a list of Among Students, tuples, where each tuple consists of a verb followed by what a sequence of noun phrases and prepositions, e.g. the little cat sat on the mat becomes ( 'sat' , 'on' , 'NP' ) . #9733; The Penn Treebank contains a section of tagged Wall Street Journal text that has been chunked into noun phrases. The format uses square brackets, and Debt College Essay we have encountered it several times during this chapter. The Treebank corpus can be accessed using: for sent in nltk.corpus.treebank_chunk.chunked_sents(fileid) . These are flat trees, just as we got using nltk.corpus.conll2000.chunked_sents() . The functions nltk.tree.pprint() and nltk.chunk.tree2conllstr() can be used to objektif hubungan etnik, create Treebank and Credit Debt Among Students IOB strings from economics, a tree. Write functions chunk2brackets() and chunk2iob() that take a single chunk tree as their sole argument, and return the required multi-line string representation. Write command-line conversion utilities bracket2iob.py and iob2bracket.py that take a file in Treebank or CoNLL format (resp) and convert it to the other format. (Obtain some raw Treebank or CoNLL data from the NLTK Corpora, save it to a file, and then use for line in Among College Essay, open(filename) to biology, access it from Python.) #9733; An n-gram chunker can use information other than the current part-of-speech tag and the n-1 previous chunk tags.
Investigate other models of the context, such as the n-1 previous part-of-speech tags, or some combination of previous chunk tags along with previous and following part-of-speech tags. Card Debt College! #9733; Consider the way an n-gram tagger uses recent tags to inform its tagging choice. Now observe how a chunker may re-use this sequence information. Economics Out! For example, both tasks will make use of the information that nouns tend to follow adjectives (in English). Card Among College! It would appear that the same information is being maintained in two places. Is this likely to did the us send troops, become a problem as the size of the rule sets grows? If so, speculate about any ways that this problem might be addressed.
About this document. UPDATED FOR NLTK 3.0. This is a chapter from Natural Language Processing with Python , by Card Debt Among College Students Essay Steven Bird, Ewan Klein and Edward Loper, Copyright © 2014 the authors. It is distributed with the of lord, Natural Language Toolkit [ http://nltk.org/ ], Version 3.0, under the Credit College Essay, terms of the Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License [http://creativecommons.org/licenses/by-nc-nd/3.0/us/]. This document was built on Wed 1 Jul 2015 12:30:05 AEST.
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50 essays authors They are poets, playwrights, novelists and scholars, and together they helped capture the voice of a nation. Card Debt Essay! They have fearlessly explored racism, abuse and objektif hubungan etnik, violence as well as love, beauty and music. While their names and styles have changed over Card Debt Among College Students Essay the years, they have been the voices of their generations and genre of lord, helped inspire the generations that followed them. What follows is a list of prominent Black authors who have left a mark on the literary world forever. Who would make your list? Add your thoughts in comment below.
Acclaimed American poet, author and activist Maya Angelou was born in St. Louis, Missouri in 1928. Often referred to as a spokesman for African Americans and women through her many works, her gift of words connected all people who were “committed to raising the moral standards of living in Credit Card Debt College Students Essay, the United States.”  “I want to write so that the reader … can say, ‘You know, that’s the truth. I wasn’t there, and I wasn’t a six-foot black girl, but that’s the truth.’ ”  Influenced by Black authors like Langston Hughes, W.E.B. What! Du Bois and Card College Students, Paul Lawrence Dunbar, her love of rene language developed at a young age. Her most famous work I Know Why the Caged Bird Sings was published in 1969 and became the first in seven autobiographies of Angelou’s life. A prolific poet, her words often depict Black beauty, the strength of women and the human spirit, and the demand for Students Essay social justice. Her first collection of the scapegoat girard poems Just Give Me a Cool Drink of Water ‘fore I Diiie was nominated for a Pulitzer Prize in 1972, the same year she became the first Black woman to have a screenplay produced.
Writing for adults and children, Angelou was one of several African American women at Debt College, the time who explored the Black female autobiographical tradition. Other female authors and genre of the, contemporaries include Paule Marshall who published the novel Brown Girl, Brownstones and Debt Among College Students Essay, Illinois Poet Laureate Gwendolyn Brooks, many of whose poems lyricize the urban poor. Image: 1970 Photo of Maya Angelou by Michael Ochs Archives/Getty Images. Though he spent most of what is sex linkage his life living abroad to escape the racial prejudice in Credit Card Debt Among, the United States, James Baldwin is the quintessential American writer. Best known for his reflections on his experience as an openly gay Black man in white America, his novels, essays and poetry make him a social critic who shared the pain and struggle of Black Americans. Born in Harlem in 1924, Baldwin caught the attention of fellow writer Richard Wright who helped him secure a grant in economics crowding, order to support himself as a writer. He left to live in Card Debt Among College Students Essay, Paris at age 24 and went on to write Go Tell it on the Mountain which was published in 1953, a novel unlike anything written to what linkage, date. Speaking with passion and depth about the Black struggle in America, it has become an American classic. Baldwin would continue to write novels, poetry and essays with a refreshingly unique perspective for the rest of his life. In 1956, Giovanni’s Room raised the issues of Debt Among College Students Essay race and homosexuality at a time when it was taboo.
And during the Civil Rights Movement, he published three of his most important collections of essays, “Notes of a Native Son” (1955), “Nobody Knows My Name” (1961) and “ The Fire Next Time” (1963) . James Baldwin provided inspiration for later generations of etnik artists to speak out about the gay experience in Black America like Staceyann Chin and Nick Burd. Image: Baldwin, 1982, MDCarchives. Born in 1934, poet, writer and political activist Amiri Baraka used his writing as a weapon against College Essay racism and became one of the most widely published African American writers. Known for his social criticism and incendiary style, Baraka explored the is sex linkage anger of Black Americans and advocated scientific socialism. Often confrontational and designed to awaken audiences to the political needs of Black Americans, Baraka was a prominent voice in American literature. Inciting controversy throughout his career, he was accused of Credit College Students fostering hate while at the same time being lauded for speaking out against oppression.
Often focusing on Black Liberation and White Racism, he spent most of his life fighting for the rights of African Americans. Economics Crowding! With a writing career that spanned nearly fifty years, Baraka is Credit Card Debt College Students respected as one of the leading revolutionary cultural and political leaders, especially in his hometown of Newark, NJ. His representations of race and wisdom have made him an influential part of the Black Arts Movement along with Nikki Giovanni, Sonia Sanchez and when troops, Maya Angelou. Together they have gone on Card College, to inspire younger generations like Terrence Hayes. Image: Poet Amiri Baraka on May 10, 1975 (Photo by Santi Visalli/Getty Images) In a genre known for being traditionally white and male, Octavia Butler broke new ground in science fiction as an African American woman. Us Send Troops To Vietnam! Born in California in Debt Among College Essay, 1947, Butler was an avid reader despite having dyslexia, was a storyteller by 4, and began writing at the age of 10. Economics Crowding! Drawn to science fiction because of Card College its boundless possibilities for imagination, she was quickly frustrated by did the us send troops to vietnam the lack of people she could identify with so she decided to create her own. Butler took the science fiction world by storm.
Her evocative novels featuring race, sex, power and humanity were highly praised and Among Essay, attracted audience beyond their genre. They would eventually be translated into multiple languages and did the us send, sell more than a million copies. One of her best-known novels Kindred , published in 1979, tells the story of a Black woman who must travel back in time in order to save her own life by saving a white, slaveholding ancestor. Over her career, she won two Hugo Awards, two Nebula Awards and in Credit Debt Essay, 1995 she became the first science fiction writer to win the MacArthur fellowship. The self-described “outsider’s” legacy inspired future generations of women including Valjeanne Jeffers, Nnedi Okorafor and even singer/songwriter Janelle Monae. Image: Butler at book signing, released by Nikolas Coukouma. As an activist, Pan-Africanist, sociologist, educator, historian and prolific writer, W.E.B. Du Bois was one of the most influential African American thought leaders of the 20 th century. Growing up in Massachusetts as part of the Black elite, it wasn’t until attending Fisk University in Tennessee that issues of racial prejudice came to his attention.
He studied Black America and wrote some of the earliest scientific studies on Black communities, calling for an end to racism. His thesis, The Suppression of the niches biology African Slave-Trade to the United States of Debt Among Students America, 1638-1870 remains an authoritative work on the subject. The horrific lynching of Sam Hose in 1899 prompted Du Bois to begin writing The Souls of Black Folk. Calling for organized action and an end to segregation, Jim Crow laws, and political disenfranchisement in America, the prophetic work was not well received at genre, the time of its publication. Du Bois eventually went on to help to establish the NAACP where he became editor of its newspaper the Credit Card Students Crisis , and a well-known spokesman for what is sex the cause. Many of his essays from Crisis were published in Credit Among Students, book form under the title The Emerging Thought of did the us send W. E. B. Du Bois: Essays and Editorials from The Crisis. In addition to The Souls of Credit Card Debt Students Black Folk and niches, the articles and editorials for the Crisis , Du Bois wrote several books. While these attracted less attention than his scholarly works, the also focused on the Black race covering the topics of miscegenation and economic disparities in the South. Most respected for Credit Card Among Students his scholarly writing, Du Bois’ concepts such as the psychology of colonization explored by soalan Frantz Fanon continued being researched years later. Image: W.E.B. Du Bois, 1919, Library of Congress.
Born Ralph Waldo Ellison after the famous journalist and poet Ralph Waldo Emerson, Ellison was known for pursuing universal truths through his writing. A literary critic, writer, and scholar, Ellison taught at a variety of colleges and spent two years overseas as a Fellow of the American Academy. In an effort to transcend the starkly defined racial categories of the Card Among College Students 1950s, he was sometimes criticized for hubungan etnik choosing white society over Credit Card Debt Essay his African American identity. Identifying as an artist first, Ellison rejected the notion that one should stand for a particular ideology, refuting both Black and white stereotypes in his collection of political, social and critical essays titled Shadow and what is sex, Act . However, it was Ellison’s first novel that established his place as an important literary figure in Credit Among College, America. Published in 1952, the first lines of Invisible Man struck a chord with hundreds of thousands of genre of the flies readers, “I am an invisible man. No, I am not a spook like those who haunted Edgar Allan Poe; nor am I one of your Hollywood-movie ectoplasms. I am a man of substance, of flesh and bone, fiber and liquids – and I might even be said to Card Among, possess a mind. I am invisible, understand, simply because people refuse to see me . . . Considered one of the most important works of fiction in the 20 th century, Ellison was heavily influenced by Zora Neale Hurston and is often cited as an influence with many writers today such as ZZ Packer and Toni Morrison. Economics! Image: National Archives, United States Information Agency staff photographer. Credit Card Among! Alex Haley’s writing on the struggle of African Americans inspired nationwide interest in genealogy and popularized Black history. Niches Biology! Best known for The Autobiography of Malcolm X and the novel Roots , Haley began his writing career freelancing and struggled to make ends meet.
Eating canned sardines for weeks at a time, his big break came when Playboy magazine assigned him to interview Miles Davis. Proving to be such a success, the Credit Among College Students magazine contracted Haley to economics out, do a series of interviews with prominent African Americans. Known as “The Playboy Interviews,” Haley would eventually meet Malcolm X and Card Debt Among College Students Essay, ask permission to write his biography. The Autobiography of Malcolm X would soon become an international bestseller and Haley became a literary success. Embarking on a new ambitious project, Haley was determined to trace his ancestor’s journey from Africa to America as slaves, and to vietnam, tell the Card College story of their rise to freedom. After a decade of research and travel to West Africa, the epic novel Roots: The Saga of an did the us send, American Family was published in 1976. The book was a national sensation and Credit Card Debt College Students, won the Pulitzer Prize, eventually becoming a television miniseries that would shatter television viewing records when 130 million viewers tuned in.
If you enjoy reading Alex Haley, consider reading Jesmyn Ward and Ta-Nehisi Coates. Soalan Objektif! Image: Mickey Adair/Getty Images. A primary contributor of the Card Students Harlem Renaissance, Langston Hughes was one of the first to use jazz rhythms in his works, becoming an early innovator of the literary art form jazz poetry. While many American poets during the 1920s were writing esoteric poetry to a dwindling audience, Hughes addressed people using language, themes, attitudes and ideas that they could relate to. Influenced by genre of lord flies Paul Lawrence Dunbar, Carl Sandburg and Walt Whitman, his poetry caught the attention of novelist, critic and prolific photographer Carl Van Vechten. With Van Vechten’s help, his first collection of poetry was published in 1926. Establishing Hughes’s poetic style and commitment to Black themes and heritage, The Weary Blues had popular appeal. When his first novel Not Without Laughter was published in 1930, it won the Harmon gold medal for literature. A prolific writer known for his colorful portrayals of Black life from the Card Among Students 1920s-1960s, Hughes wrote plays, short stories, poetry, several books, and contributed the lyrics to a Broadway musical. In addition to when, his extensive body of work, he inspired other artists and highlighted the power of art as a catalyst for change. Seen as a voice for their own experience, writers during the Harlem Renaissance often dedicated their work to Hughes.
The play A Raisin in the Sun by playwright Lorraine Hansberry was named for a line from a Langston Hughes poem. Image: Langston Hughes, 1936 Carl Van Vechten, Library of Congress. In 1925 as the Harlem Renaissance gained momentum, Zora Neale Hurston headed to New York City. By the time of Card Debt Among Students Essay its height in the 1930s, Hurston was a preeminent Black female writer in the United States. It’s said that her apartment was a popular spot for soalan etnik social gatherings with the well-known artists of the time like Countee Cullen and Langston Hughes. Of Hurston’s more than 50 published novels, short stories, plays and Credit Card Debt College Essay, essays, she wrote her most famous work Their Eyes Were Watching God in 1937. Us Send Troops! Unlike the style of contemporaries Richard Wright and Ralph Ellison, Hurston did not write explicitly about Black people in the context of white America. She focused on the culture and traditions of Debt College Essay African Americans through the soalan objektif hubungan poetry of their speech. Despite her earlier literary success, Hurston would suffer later in her career. Credit Students Essay! Having difficulty getting published, she died poor and alone. Years later, Alice Walker would help revive interest in the scapegoat rene, Hurston’s work with her essay, “In Search of Zora Neale Hurston, published in Ms. magazine in 1975.
This essay, alongside her edits of Card Debt Among Essay notable works like “I Love Myself When I am Laughing and Then Again When I am Looking Mean and did the troops, Impressive,” brought Hurston to the attention of a new generation of readers. Image: Zora Neale Hurston, Photo by Carl Van Vechten (1938) Library of Congress. Born in Mississippi in 1908, Richard Wright is best known for his novels Native Son and Black Boy, that mirrored his own struggle with poverty and coming of age journey. A staunch critic of his literary contemporary Zora Neale Hurston, Wright’s work was overtly political, focusing on the struggle of Blacks in Card Debt Students Essay, America for equality and economic advancement. To Vietnam! Wright’s dreams of becoming a writer took off when he gained employment through the Federal Writers Project and received critical attention for a collection of Credit Card Among College Students short stories called Uncle Tom’s Children . The fame that came with the 1940 publication of Native Son (not to be confused with James Baldwin’s titular essay: “Notes of a Native Son,” which criticized Wright’s work) made him a household name. Crowding! It became the first book by an African American writer to be selected by the Book-of-the-Month Club. His novel Black Boy was a personal account of growing up in the South and Among Students, eventual move to Chicago where he became a writer and joined the Communist Party.
While the soalan objektif book was a great success, Wright had become disillusioned with white America and the Communist Party, and moved to Paris. He spent the rest of Card Debt Among Essay his life living as an expatriate and he continued to write novels. Image: Carl Van Vechten Collection, Library of Congress. Nobel Prize- and definition biology, Pulitzer Prize-winning novelist Toni Morrison is considered the voice of African American women. Growing up in an integrated neighborhood, Morrison was not fully aware of racial divisions until her teenage years. Dedicated to her studies, she went on to earn her master’s degree before moving to Howard University to teach. It was in the 1960s when Morrison became an editor at Random House that she began to write. While she had published The Bluest Eye in 1970 and Sula in 1973, The Song of Solomon was the book that set her on the course of literary success. It became the first work by an African American author since Native Son by Richard Wright to be a featured selection in Credit Card Debt, the Book-of-the-Month Club.
The publication of Beloved in 1987 is genre flies considered to be her greatest masterpiece and won several awards, including the Pulitzer Prize for Fiction. Young authors Danielle Evans and Branden Jacobs-Jenkins cite Toni Morrison as one of Card College Students Essay their influences.
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Enzymes: principles and biotechnological applications. Enzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions in living organisms, and which can be extracted from cells and Credit Card Debt College Students then used to catalyse a wide range of commercially important processes. This chapter covers the basic principles of enzymology, such as classification, structure, kinetics and inhibition, and also provides an overview of soalan objektif hubungan etnik industrial applications. In addition, techniques for the purification of enzymes are discussed. Enzymes are biological catalysts (also known as biocatalysts) that speed up biochemical reactions in Credit Card Debt Among College, living organisms. They can also be extracted from cells and then used to catalyse a wide range of when did the troops to vietnam commercially important processes. For example, they have important roles in the production of sweetening agents and Card Debt College Students the modification of antibiotics, they are used in washing powders and various cleaning products, and they play a key role in analytical devices and assays that have clinical, forensic and definition environmental applications. The word ‘enzyme’ was first used by the German physiologist Wilhelm Kuhne in 1878, when he was describing the ability of Debt Among Students yeast to produce alcohol from sugars, and it is rene girard derived from the Greek words en (meaning ‘within’) and Credit Card Debt Among Students Essay zume (meaning ‘yeast’). In the late nineteenth century and objektif early twentieth century, significant advances were made in Credit Card Among College Essay, the extraction, characterization and commercial exploitation of many enzymes, but it was not until the rene girard 1920s that enzymes were crystallized, revealing that catalytic activity is associated with protein molecules.
For the next 60 years or so it was believed that all enzymes were proteins, but in the 1980s it was found that some ribonucleic acid (RNA) molecules are also able to exert catalytic effects. These RNAs, which are called ribozymes, play an important role in gene expression. In the Card Debt College Essay same decade, biochemists also developed the technology to generate antibodies that possess catalytic properties. Soalan Etnik. These so-called ‘abzymes’ have significant potential both as novel industrial catalysts and in therapeutics. Notwithstanding these notable exceptions, much of classical enzymology, and the remainder of this essay, is focused on the proteins that possess catalytic activity. As catalysts, enzymes are only required in Card Debt Students, very low concentrations, and they speed up reactions without themselves being consumed during the reaction.
We usually describe enzymes as being capable of catalysing the conversion of substrate molecules into product molecules as follows: The enormous catalytic activity of rene girard enzymes can perhaps best be expressed by a constant, k cat , that is variously referred to as the turnover rate, turnover frequency or turnover number. This constant represents the number of substrate molecules that can be converted to product by a single enzyme molecule per unit time (usually per minute or per second). Examples of turnover rate values are listed in Table 1. For example, a single molecule of carbonic anhydrase can catalyse the conversion of over half a million molecules of its substrates, carbon dioxide (CO 2 ) and water (H 2 O), into the product, bicarbonate (HCO 3 ? ), every second—a truly remarkable achievement. As well as being highly potent catalysts, enzymes also possess remarkable specificity in Credit Card College Essay, that they generally catalyse the conversion of only objektif etnik, one type (or at most a range of similar types) of Debt substrate molecule into product molecules. Some enzymes demonstrate group specificity. For example, alkaline phosphatase (an enzyme that is commonly encountered in first-year laboratory sessions on enzyme kinetics) can remove a phosphate group from a variety of soalan objektif hubungan etnik substrates.
Other enzymes demonstrate much higher specificity, which is described as absolute specificity. For example, glucose oxidase shows almost total specificity for Credit Debt its substrate, ?-D-glucose, and virtually no activity with any other monosaccharides. As we shall see later, this specificity is of paramount importance in out, many analytical assays and devices (biosensors) that measure a specific substrate (e.g. glucose) in Credit Card Debt College, a complex mixture (e.g. The Scapegoat Rene Girard. a blood or urine sample). Enzymes typically have common names (often called ‘trivial names’) which refer to the reaction that they catalyse, with the suffix -ase (e.g. oxidase, dehydrogenase, carboxylase), although individual proteolytic enzymes generally have the Among Students suffix - in (e.g. trypsin, chymotrypsin, papain). Economics Crowding Out. Often the trivial name also indicates the Debt Among Students Essay substrate on which the enzyme acts (e.g. glucose oxidase, alcohol dehydrogenase, pyruvate decarboxylase). However, some trivial names (e.g. invertase, diastase, catalase) provide little information about the substrate, the product or the reaction involved.
Due to the growing complexity of and inconsistency in the naming of economics crowding out enzymes, the International Union of Biochemistry set up the Credit Card Debt Among Essay Enzyme Commission to address this issue. The first Enzyme Commission Report was published in 1961, and provided a systematic approach to niches the naming of enzymes. The sixth edition, published in 1992, contained details of nearly 3 200 different enzymes, and supplements published annually have now extended this number to over 5 000. Within this system, all enzymes are described by a four-part Enzyme Commission (EC) number. Credit Card Debt College Students. For example, the enzyme with the linkage trivial name lactate dehydrogenase has the EC number 126.96.36.199, and is more correctly called l –lactate: NAD + oxidoreductase. The first part of the EC number refers to the reaction that the enzyme catalyses (Table 2).
The remaining digits have different meanings according to the nature of the reaction identified by the first digit. Credit Card Debt College Students Essay. For example, within the objektif etnik oxidoreductase category, the second digit denotes the hydrogen donor (Table 3) and the third digit denotes the hydrogen acceptor (Table 4). Thus lactate dehydrogenase with the EC number 188.8.131.52 is an oxidoreductase (indicated by the first digit) with the alcohol group of the lactate molecule as the hydrogen donor (second digit) and NAD + as the Card Debt Among College Students Essay hydrogen acceptor (third digit), and is the 27th enzyme to be categorized within this group (fourth digit). Fortunately, it is now very easy to find this information for any individual enzyme using the Enzyme Nomenclature Database (available at when to vietnam, http://enzyme.expasy.org). Enzyme structure and substrate binding. Amino acid-based enzymes are globular proteins that range in size from less than 100 to more than 2 000 amino acid residues. These amino acids can be arranged as one or more polypeptide chains that are folded and bent to form a specific three-dimensional structure, incorporating a small area known as the active site (Figure 1), where the substrate actually binds. The active site may well involve only a small number (less than 10) of the constituent amino acids. It is the shape and charge properties of the active site that enable it to bind to a single type of substrate molecule, so that the enzyme is able to demonstrate considerable specificity in its catalytic activity.
The hypothesis that enzyme specificity results from the Card Debt College Essay complementary nature of the niches substrate and its active site was first proposed by the German chemist Emil Fischer in Card Essay, 1894, and became known as Fischer's ‘lock and key hypothesis’, whereby only a key of the correct size and shape (the substrate) fits into us send troops the keyhole (the active site) of the lock (the enzyme). It is astounding that this theory was proposed at a time when it was not even established that enzymes were proteins. As more was learned about enzyme structure through techniques such as X-ray crystallography, it became clear that enzymes are not rigid structures, but are in fact quite flexible in shape. In the light of this finding, in 1958 Daniel Koshland extended Fischer's ideas and presented the ‘induced-fit model’ of substrate and enzyme binding, in Card Students Essay, which the enzyme molecule changes its shape slightly to accommodate the is sex binding of the Among College Students Essay substrate. The analogy that is the scapegoat rene commonly used is the ‘hand-in-glove model’, where the hand and glove are broadly complementary in shape, but the glove is moulded around the hand as it is inserted in order to provide a perfect match. Since it is the active site alone that binds to the substrate, it is logical to ask what is the role of the Credit Debt Among Essay rest of the protein molecule.
The simple answer is that it acts to stabilize the active site and provide an appropriate environment for interaction of the site with the substrate molecule. Therefore the active site cannot be separated out from the rest of the when protein without loss of catalytic activity, although laboratory-based directed (or forced) evolution studies have shown that it is College Essay sometimes possible to biology generate smaller enzymes that do retain activity. It should be noted that although a large number of enzymes consist solely of protein, many also contain a non-protein component, known as a cofactor, that is necessary for the enzyme's catalytic activity. A cofactor may be another organic molecule, in which case it is called a coenzyme, or it may be an inorganic molecule, typically a metal ion such as iron, manganese, cobalt, copper or zinc. A coenzyme that binds tightly and permanently to Credit Card Among Students Essay the protein is generally referred to as the is sex prosthetic group of the Card Debt College Students Essay enzyme. When an enzyme requires a cofactor for its activity, the inactive protein component is generally referred to as an apoenzyme, and the apoenzyme plus the cofactor (i.e. the active enzyme) is called a holoenzyme (Figure 2).
The need for minerals and genre of the vitamins in the human diet is partly attributable to their roles within metabolism as cofactors and coenzymes. How do enzymes work? The broad answer to this question is that they do not alter the equilibrium (i.e. the thermodynamics) of a reaction. This is because enzymes do not fundamentally change the structure and Credit Debt College Students energetics of the products and reagents, but rather they simply allow the reaction equilibrium to be attained more rapidly. Hubungan Etnik. Let us therefore begin by clarifying the concept of chemical equilibrium. In many cases the equilibrium of a reaction is far ‘to the Among College Students Essay right’—that is, virtually all of the substrate (S) is converted into product (P). For this reason, reactions are often written as follows: This is a simplification, as in all cases it is more correct to write this reaction as follows: This indicates the presence of an equilibrium.
To understand this concept it is perhaps most helpful to rene girard look at a reaction where the equilibrium point is quite central. In this reaction, if we start with a solution of 1 mol l ?1 glucose and add the enzyme, then upon completion we will have a mixture of approximately 0.5 mol l ?1 glucose and 0.5 mol l ?1 fructose. This is the equilibrium point of this particular reaction, and although it may only take a couple of seconds to reach this end point with the enzyme present, we would in fact come to the same point if we put glucose into Card Among College Students Essay solution and waited many months for the reaction to occur in the absence of the enzyme. Interestingly, we could also have started this reaction with a 1 mol l ?1 fructose solution, and it would have proceeded in the opposite did the us send troops to vietnam direction until the same equilibrium point had been reached. The equilibrium point for this reaction is expressed by the equilibrium constant K eq as follows: Thus for a reaction with central equilibrium, K eq = 1, for Credit Among College an equilibrium ‘to the right’ K eq is 1, and for an equilibrium ‘to the left’ K eq is what linkage 1. Therefore if a reaction has a K eq value of Card 10 6 , the equilibrium is very far to biology the right and Credit Among College Students Essay can be simplified by denoting it as a single arrow. We may often describe this type of reaction as ‘going to completion’. Conversely, if a reaction has a K eq value of 10 ?6 , the equilibrium is soalan objektif hubungan etnik very far to Card College Students the left, and for all practical purposes it would not really be considered to proceed at all. It should be noted that although the concentration of reactants has no effect on the scapegoat rene girard, the equilibrium point, environmental factors such as pH and temperature can and do affect the position of the equilibrium. It should also be noted that any biochemical reaction which occurs in vivo in Credit Card Debt Among College Essay, a living system does not occur in girard, isolation, but as part of a metabolic pathway, which makes it more difficult to conceptualize the relationship between reactants and Debt College Students reactions.
In vivo reactions are not allowed to proceed to their equilibrium position. Is Sex Linkage. If they did, the reaction would essentially stop (i.e. the forward and reverse reactions would balance each other), and there would be no net flux through the pathway. However, in many complex biochemical pathways some of the individual reaction steps are close to equilibrium, whereas others are far from equilibrium, the latter (catalysed by regulatory enzymes) having the greatest capacity to control the Credit College Essay overall flux of materials through the pathway. Enzymes form complexes with their substrates. We often describe an enzyme-catalysed reaction as proceeding through three stages as follows: The ES complex represents a position where the substrate (S) is bound to the enzyme (E) such that the reaction (whatever it might be) is made more favourable. As soon as the reaction has occurred, the product molecule (P) dissociates from the enzyme, which is then free to bind to another substrate molecule.
At some point during this process the the scapegoat rene girard substrate is converted into an intermediate form (often called the transition state) and then into the product. The exact mechanism whereby the enzyme acts to increase the rate of the reaction differs from one system to another. However, the general principle is Credit Debt Among College that by binding of the substrate to the enzyme, the reaction involving the substrate is linkage made more favourable by lowering the activation energy of the reaction. In terms of Debt Students energetics, reactions can be either exergonic (releasing energy) or endergonic (consuming energy). However, even in an exergonic reaction a small amount of energy, termed the activation energy, is of the needed to give the reaction a ‘kick start.’ A good analogy is that of a match, the Debt Among Essay head of which contains a mixture of what energy-rich chemicals (phosphorus sesquisulfide and Among Students Essay potassium chlorate). When a match burns it releases substantial amounts of light and heat energy (exergonically reacting with O 2 in the air). Of Lord Of The Flies. However, and perhaps fortunately, a match will not spontaneously ignite, but rather a small input of energy in the form of heat generated through friction (i.e. striking of the match) is needed to initiate the Credit College Students Essay reaction. Of course once the match has been struck the amount of energy released is considerable, and greatly exceeds the small energy input during the striking process. As shown in what is sex, Figure 3, enzymes are considered to Card College lower the activation energy of a system by making it energetically easier for the transition state to form.
In the presence of an enzyme catalyst, the formation of the transition state is energetically more favourable (i.e. it requires less energy for the ‘kick start’), thereby accelerating the niches definition rate at which the reaction will proceed, but not fundamentally changing the energy levels of either the reactant or the product. Properties and mechanisms of enzyme action. Enzyme kinetics is the study of Among College Students Essay factors that determine the speed of enzyme-catalysed reactions. It utilizes some mathematical equations that can be confusing to students when they first encounter them. However, the theory of kinetics is both logical and did the us send troops simple, and Debt Students Essay it is essential to develop an understanding of this subject in order to be able to appreciate the the scapegoat rene role of enzymes both in metabolism and in biotechnology. Assays (measurements) of enzyme activity can be performed in either a discontinuous or continuous fashion. Discontinuous methods involve mixing the substrate and enzyme together and measuring the product formed after a set period of Debt Among College Essay time, so these methods are generally easy and quick to perform. In general we would use such discontinuous assays when we know little about the system (and are making preliminary investigations), or alternatively when we know a great deal about the rene girard system and are certain that the time interval we are choosing is appropriate. In continuous enzyme assays we would generally study the Credit Debt College Essay rate of an when us send, enzyme-catalysed reaction by Credit Card Among Essay, mixing the enzyme with the substrate and continuously measuring the appearance of product over time. Of course we could equally well measure the rate of the reaction by measuring the disappearance of substrate over time. Apart from the actual direction (one increasing and genre one decreasing), the two values would be identical.
In enzyme kinetics experiments, for Credit Debt Among College convenience we very often use an artificial substrate called a chromogen that yields a brightly coloured product, making the reaction easy to follow using a colorimeter or a spectrophotometer. However, we could in fact use any available analytical equipment that has the capacity to measure the concentration of either the product or the substrate. In almost all cases we would also add a buffer solution to the mixture. As we shall see, enzyme activity is strongly influenced by pH, so it is important to set the pH at a specific value and genre keep it constant throughout the experiment. Our first enzyme kinetics experiment may therefore involve mixing a substrate solution (chromogen) with a buffer solution and Debt College adding the enzyme. This mixture would then be placed in a spectrophotometer and the appearance of the coloured product would be measured. This would enable us to crowding follow a rapid reaction which, after a few seconds or minutes, might start to slow down, as shown in Figure 4. A common reason for this slowing down of the speed (rate) of the reaction is Card Debt Among College Students Essay that the substrate within the mixture is being used up and thus becoming limiting. Alternatively, it may be that the niches definition biology enzyme is unstable and is denaturing over the course of the experiment, or it could be that the pH of the mixture is changing, as many reactions either consume or release protons.
For these reasons, when we are asked to specify the rate of a reaction we do so early on, as soon as the enzyme has been added, and when none of the above-mentioned limitations apply. We refer to this initial rapid rate as the Debt Among College initial velocity ( v 0 ). Genre Of Lord Of The. Measurement of the reaction rate at this early stage is also quite straightforward, as the rate is effectively linear, so we can simply draw a straight line and Credit College Essay measure the gradient (by dividing the concentration change by the time interval) in biology, order to Credit Card Students Essay evaluate the reaction rate over this period. We may now perform a range of similar enzyme assays to evaluate how the initial velocity changes when the substrate or enzyme concentration is altered, or when the pH is changed. These studies will help us to characterize the properties of the enzyme under study. The relationship between enzyme concentration and the rate of the economics out reaction is Debt Among College usually a simple one.
If we repeat the experiment just described, but add 10% more enzyme, the objektif hubungan etnik reaction will be 10% faster, and if we double the enzyme concentration the reaction will proceed twice as fast. Thus there is Debt Among a simple linear relationship between the reaction rate and the amount of enzyme available to catalyse the reaction (Figure 5). This relationship applies both to enzymes in vivo and to those used in biotechnological applications, where regulation of the amount of enzyme present may control reaction rates. When we perform a series of enzyme assays using the same enzyme concentration, but with a range of economics crowding different substrate concentrations, a slightly more complex relationship emerges, as shown in Card Among College Students, Figure 6. Initially, when the substrate concentration is increased, the rate of rene girard reaction increases considerably. However, as the substrate concentration is Credit Debt Among increased further the effects on the reaction rate start to decline, until a stage is reached where increasing the substrate concentration has little further effect on the reaction rate. At this point the niches definition enzyme is considered to be coming close to saturation with substrate, and demonstrating its maximal velocity ( V max ). Note that this maximal velocity is in Debt College Essay, fact a theoretical limit that will not be truly achieved in any experiment, although we might come very close to soalan hubungan it. The relationship described here is a fairly common one, which a mathematician would immediately identify as a rectangular hyperbola. The equation that describes such a relationship is as follows: The two constants a and Credit Among Students b thus allow us to describe this hyperbolic relationship, just as with a linear relationship ( y = mx + c ), which can be expressed by the two constants m (the slope) and c (the intercept).
We have in fact already defined the constant a — it is V max . The constant b is a little more complex, as it is the value on the x -axis that gives half of the economics crowding out maximal value of Card Debt Among Students y . In enzymology we refer to this as the Michaelis constant ( K m ), which is defined as the rene substrate concentration that gives half-maximal velocity. Our final equation, usually called the Michaelis–Menten equation, therefore becomes: In 1913, Leonor Michaelis and Maud Menten first showed that it was in fact possible to derive this equation mathematically from first principles, with some simple assumptions about the way in which an Credit Card College Essay, enzyme reacts with a substrate to form a product. Central to their derivation is the concept that the reaction takes place via the formation of an genre of lord, ES complex which, once formed, can either dissociate (productively) to release product, or else dissociate in the reverse direction without any formation of Card Debt Among College product. Thus the reaction can be represented as follows, with k 1 , k ?1 and k 2 being the rate constants of the three individual reaction steps: The Michaelis–Menten derivation requires two important assumptions. The first assumption is that we are considering the initial velocity of the reaction ( v 0 ), when the product concentration will be negligibly small (i.e. [S] ? [P]), such that we can ignore the biology possibility of any product reverting to substrate. Card Debt Among Students Essay. The second assumption is that the concentration of flies substrate greatly exceeds the concentration of enzyme (i.e. [S]?[E]). The derivation begins with an equation for the expression of the Among Essay initial rate, the rate of when did the troops formation of product, as the rate at which the Debt Among College Students Essay ES complex dissociates to form product.
This is based upon the rate constant k 2 and the concentration of the ES complex, as follows: 1. Since ES is an intermediate, its concentration is unknown, but we can express it in terms of known values. In a steady-state approximation we can assume that although the concentration of substrate and product changes, the us send concentration of the ES complex itself remains constant. The rate of formation of the ES complex and Credit Card Students Essay the rate of its breakdown must therefore balance, where: and. Hence, at steady state: This equation can be rearranged to yield [ES] as follows: 2. The Michaelis constant K m can be defined as follows: Equation 2 may thus be simplified to: 3. Since the concentration of when did the troops substrate greatly exceeds the Debt concentration of enzyme (i.e. [S] ? [E]), the crowding concentration of uncombined substrate [S] is Credit College Essay almost equal to the total concentration of substrate. The concentration of flies uncombined enzyme [E] is Card Debt equal to the total enzyme concentration [E] T minus that combined with substrate [ES].
Introducing these terms to definition Equation 3 and Card Among College Essay solving for objektif hubungan ES gives us the following: 4. We can then introduce this term into Equation 1 to give: 5. The term k 2 [E] T in fact represents V max , the maximal velocity. Thus Michaelis and Menten were able to derive their final equation as: A more detailed derivation of the Credit Card Students Essay Michaelis–Menten equation can be found in many biochemistry textbooks (see section 4 of Recommended Reading section). There are also some very helpful web-based tutorials available on the subject. Michaelis constants have been determined for economics out many commonly used enzymes, and Credit Card Debt Among College Students are typically in the lower millimolar range (Table 5). It should be noted that enzymes which catalyse the same reaction, but which are derived from different organisms, can have widely differing K m values. Objektif Hubungan. Furthermore, an enzyme with multiple substrates can have quite different K m values for each substrate.
A low K m value indicates that the enzyme requires only a small amount of Credit Students Essay substrate in order to become saturated. Of Lord Flies. Therefore the maximum velocity is reached at relatively low substrate concentrations. A high K m value indicates the need for high substrate concentrations in order to achieve maximum reaction velocity. Thus we generally refer to Card Among K m as a measure of the the scapegoat rene affinity of the Card Debt Among enzyme for its substrate—in fact it is an genre of the flies, inverse measure, where a high K m indicates a low affinity, and vice versa. The K m value tells us several important things about Credit Among Essay, a particular enzyme. An enzyme with a low K m value relative to the physiological concentration of soalan objektif etnik substrate will probably always be saturated with substrate, and will therefore act at a constant rate, regardless of Credit Card variations in the concentration of substrate within the physiological range. An enzyme with a high K m value relative to the physiological concentration of substrate will not be saturated with substrate, and its activity will therefore vary according to the concentration of substrate, so the soalan etnik rate of formation of product will depend on Credit College Students Essay, the availability of substrate. If an enzyme acts on several substrates, the substrate with the lowest K m value is frequently assumed to be that enzyme's ‘natural’ substrate, although this may not be true in all cases. If two enzymes (with similar V max ) in different metabolic pathways compete for the same substrate, then if we know the K m values for the two enzymes we can predict the relative activity of the two pathways.
Essentially the economics out pathway that has the enzyme with the lower K m value is Credit Among College Essay likely to be the ‘preferred pathway’, and more substrate will flow through that pathway under most conditions. For example, phosphofructokinase (PFK) is the enzyme that catalyses the first committed step in the glycolytic pathway, which generates energy in what, the form of Credit Debt College Students Essay ATP for the cell, whereas glucose-1-phosphate uridylyltransferase (GUT) is an enzyme early in the pathway leading to the synthesis of glycogen (an energy storage molecule). Both enzymes use hexose monophosphates as substrates, but the K m of PFK for its substrate is lower than that of GUT for its substrate. Thus at the scapegoat rene girard, lower cellular hexose phosphate concentrations, PFK will be active and GUT will be largely inactive. Credit Card Debt Among. At higher hexose phosphate concentrations both pathways will be active. This means that the cells only store glycogen in times of plenty, and always give preference to the pathway of ATP production, which is the more essential function. Very often it is not possible to estimate K m values from a direct plot of velocity against substrate concentration (as shown in Figure 6) because we have not used high enough substrate concentrations to come even close to the scapegoat rene estimating maximal velocity, and therefore we cannot evaluate half-maximal velocity and thus K m . Fortunately, we can plot our experimental data in a slightly different way in order to Credit Among Essay obtain these values. The most commonly used alternative is the Lineweaver–Burk plot (often called the double-reciprocal plot). This plot linearizes the hyperbolic curved relationship, and the line produced is easy to extrapolate, allowing evaluation of V max and K m . For example, if we obtained only the did the us send first seven data points in Figure 6, we would have difficulty estimating V max from a direct plot as shown in Figure 7a.
However, as shown in Figure 7b, if these seven points are plotted on a graph of 1/velocity against 1/substrate concentration (i.e. a double-reciprocal plot), the data are linearized, and the line can be easily extrapolated to Credit Card College the left to genre of lord provide intercepts on both the y -axis and the x -axis, from which V max and K m , respectively, can be evaluated. One significant practical drawback of using the Credit College Lineweaver–Burk plot is the excessive influence that it gives to measurements made at the lowest substrate concentrations. These concentrations might well be the most prone to error (due to difficulties in making multiple dilutions), and result in reaction rates that, because they are slow, might also be most prone to measurement error. Often, as shown in Figure 8, such points when transformed on the Lineweaver–Burk plot have a significant impact on the line of best fit estimated from the data, and crowding therefore on the extrapolated values of Credit Card Among College Essay both V max and K m . Niches Definition Biology. The two sets of points shown in Figure 8 are identical except for the single point at the top right, which reflects (because of the plot's double-reciprocal nature) a single point derived from a very low substrate concentration and Credit Card Debt a low reaction rate. However, this single point can have an enormous impact on genre of lord of the flies, the line of best fit and the accompanying estimates of kinetic constants. In fact there are other kinetic plots that can be used, including the Eadie–Hofstee plot, the Hanes plot and the Eisenthal–Cornish-Bowden plot, which are less prone to Card Debt Students Essay such problems. However, the did the to vietnam Lineweaver–Burk plot is Among Students still the most commonly described kinetic plot in the majority of enzymology textbooks, and thus retains its influence in undergraduate education. Enzymes are affected by pH and temperature. Various environmental factors are able to affect the rate of enzyme-catalysed reactions through reversible or irreversible changes in the protein structure. The effects of pH and temperature are generally well understood.
Most enzymes have a characteristic optimum pH at which the velocity of the catalysed reaction is maximal, and above and below which the velocity declines (Figure 9). The pH profile is when did the troops to vietnam dependent on a number of factors. As the pH changes, the ionization of groups both at the enzyme's active site and on the substrate can alter, influencing the rate of binding of the substrate to the active site. These effects are often reversible. Credit Card Among College Students. For example, if we take an enzyme with an optimal pH (pH opt ) of 7.0 and place it in an environment at pH 6.0 or 8.0, the charge properties of the enzyme and the substrate may be suboptimal, such that binding and hence the reaction rate are lowered. If we then readjust the pH to 7.0, the what is sex linkage optimal charge properties and hence the maximal activity of the enzyme are often restored. Card Among Students. However, if we place the enzyme in a more extreme acidic or alkaline environment (e.g. at pH 1 or 14), although these conditions may not actually lead to changes in the very stable covalent structure of the objektif etnik protein (i.e. its configuration), they may well produce changes in the conformation (shape) of the protein such that, when it is returned to pH 7.0, the original conformation and hence the Credit Debt College Students Essay enzyme's full catalytic activity are not restored. It should be noted that the optimum pH of an enzyme may not be identical to that of its normal intracellular surroundings. Girard. This indicates that the local pH can exert a controlling influence on enzyme activity. The effects of temperature on Credit Card Essay, enzyme activity are quite complex, and can be regarded as two forces acting simultaneously but in opposite directions. As the etnik temperature is raised, the rate of molecular movement and hence the rate of reaction increases, but at Credit Card, the same time there is a progressive inactivation caused by denaturation of the enzyme protein.
This becomes more pronounced as the temperature increases, so that an apparent temperature optimum (T opt ) is observed (Figure 10). Thermal denaturation is time dependent, and for an enzyme the term ‘optimum temperature’ has little real meaning unless the duration of exposure to that temperature is recorded. The thermal stability of an enzyme can be determined by first exposing the protein to out a range of temperatures for a fixed period of time, and subsequently measuring its activity at one favourable temperature (e.g. 25°C). The temperature at which denaturation becomes important varies from one enzyme to another. Normally it is negligible below 30°C, and starts to become appreciable above 40°C. Typically, enzymes derived from microbial sources show much higher thermal stability than do those from Credit Card Debt Among College Students Essay mammalian sources, and enzymes derived from extremely thermophilic microorganisms, such as thermolysin (a protease from Bacillus thermoproteolyticus ) and Taq polymerase (a DNA polymerase from Thermus aquaticus ), might be completely thermostable at 70°C and still retain substantial levels of activity even at 100°C. Enzymes are sensitive to inhibitors. Substances that reduce the activity of an enzyme-catalysed reaction are known as inhibitors.
They act by the scapegoat rene girard, either directly or indirectly influencing the catalytic properties of the active site. Inhibitors can be foreign to Credit Card Among College Students the cell or natural components of it. Those in us send to vietnam, the latter category can represent an important element of the regulation of cell metabolism. Credit Card Debt College Students. Many toxins and hubungan etnik also many pharmacologically active agents (both illegal drugs and prescription and over-the-counter medicines) act by inhibiting specific enzyme-catalysed processes. Inhibitors are classified as reversible inhibitors when they bind reversibly to an enzyme. A molecule that is structurally similar to the normal substrate may be able to bind reversibly to the enzyme's active site and therefore act as a competitive inhibitor.
For example, malonate is a competitive inhibitor of the enzyme succinate dehydrogenase, as it is capable of binding to the enzyme's active site due to Credit Card its close structural similarity to the enzyme's natural substrate, succinate (see below). When malonate occupies the active site of succinate dehydrogenase it prevents the natural substrate, succinate, from binding, thereby slowing down the rate of oxidation of succinate to fumarate (i.e. inhibiting the reaction). One of the did the characteristics of competitive inhibitors is that they can be displaced from the active site if high concentrations of substrate are used, thereby restoring enzyme activity. Credit Debt Students. Thus competitive inhibitors increase the K m of a reaction because they increase the concentration of economics crowding out substrate required to saturate the enzyme. However, they do not change V max itself.
In the case of certain enzymes, high concentrations of either the substrate or the product can be inhibitory. For example, invertase activity is considerably reduced in the presence of high concentrations of sucrose (its substrate), whereas the ?-galactosidase of Aspergillus niger is Debt Among College Essay strongly inhibited by galactose (its product). Niches Definition. Products of an enzyme reaction are some of the most commonly encountered competitive inhibitors. Other types of reversible inhibitor also exist. Credit Debt Essay. Non-competitive inhibitors react with the enzyme at a site distinct from the active site. Therefore the binding of the inhibitor does not physically block the substrate–binding site, but it does prevent subsequent reaction. Most non-competitive inhibitors are chemically unrelated to the substrate, and their inhibition cannot be overcome by increasing the substrate concentration. Such inhibitors in effect reduce the concentration of the active enzyme in solution, thereby reducing the V max of the reaction. However, they do not change the objektif hubungan value of Card Debt Among Students Essay K m . Uncompetitive inhibition is rather rare, occurring when the economics inhibitor is only able to bind to the enzyme once a substrate molecule has itself bound. As such, inhibition is most significant at high substrate concentrations, and results in a reduction in the V max of the reaction. Uncompetitive inhibition also causes a reduction in K m , which seems somewhat counterintuitive as this means that the affinity of the Debt Among Essay enzyme for its substrate is actually increased when the inhibitor is present.
This effect occurs because the binding of the inhibitor to the ES complex effectively removes ES complex and thereby affects the overall equilibrium of the reaction favouring ES complex formation. It is noteworthy however that since both V max and K m are reduced the observed reaction rates with inhibitor present are always lower than those in the absence of the uncompetitive inhibitor. Irreversible inhibitors and poisons. If an inhibitor binds permanently to an enzyme it is known as an irreversible inhibitor. Many irreversible inhibitors are therefore potent toxins. Organophosphorus compounds such as diisopropyl fluorophosphate (DFP) inhibit acetylcholinesterase activity by reacting covalently with an important serine residue found within the crowding out active site of the enzyme. The physiological effect of this inactivation is interference with neurotransmitter inactivation at the synapses of nerves, resulting in the constant propagation of nerve impulses, which can lead to death.
DFP was originally evaluated by Credit Card Debt College Students, the British as a chemical warfare agent during World War Two, and modified versions of this compound are now widely used as organophosphate pesticides (e.g. When Did The Us Send Troops. parathione, malathione). Allosteric regulators and the control of enzyme activity. Having spent time learning about enzyme kinetics and the Michaelis–Menten relationship, it is often quite disconcerting to find that some of the most important enzymes do not in fact display such properties. Allosteric enzymes are key regulatory enzymes that control the activities of metabolic pathways by Among College Students Essay, responding to inhibitors and is sex linkage activators. These enzymes in fact show a sigmoidal (S-shaped) relationship between reaction rate and substrate concentration (Figure 11), rather than the Debt College Essay usual hyperbolic relationship. Thus for allosteric enzymes there is an area where activity is lower than that of an equivalent ‘normal’ enzyme, and also an crowding, area where activity is higher than that of an equivalent ‘normal’ enzyme, with a rapid transition between these two phases. This is rather like a switch that can quickly be changed from ‘off’ (low activity) to ‘on’ (full activity). Most allosteric enzymes are polymeric—that is, they are composed of at least two (and often many more) individual polypeptide chains. They also have multiple active sites where the substrate can bind. Much of our understanding of the Credit Card function of allosteric enzymes comes from economics crowding out studies of haemoglobin which, although it is Credit Card College Students Essay not an enzyme, binds oxygen in a similarly co-operative way and thus also demonstrates this sigmoidal relationship. Allosteric enzymes have an initially low affinity for the substrate, but when a single substrate molecule binds, this may break some bonds within the enzyme and thereby change the shape of the protein such that the remaining active sites are able to niches bind with a higher affinity.
Therefore allosteric enzymes are often described as moving from a tensed state or T-state (low affinity) in which no substrate is bound, to Credit Card Debt Among College Students Essay a relaxed state or R-state (high affinity) as substrate binds. Other molecules can also bind to allosteric enzymes, at additional regulatory sites (i.e. not at the active site). Molecules that stabilize the protein in girard, its T-state therefore act as allosteric inhibitors, whereas molecules that move the protein to its R-state will act as allosteric activators or promoters. A good example of an allosteric enzyme is aspartate transcarbamoylase (ATCase), a key regulatory enzyme that catalyses the first committed step in the sequence of reactions that produce the Credit Essay pyrimidine nucleotides which are essential components of us send DNA and RNA. The reaction is as follows: The end product in the pathway, the pyrimidine nucleotide cytidine triphosphate (CTP), is an active allosteric inhibitor of the enzyme ATCase. Credit Debt College. Therefore when there is what linkage a high concentration of CTP in the cell, this feeds back and inhibits the ATCase enzyme, reducing its activity and thus lowering the rate of production of further pyrimidine nucleotides.
As the Card Debt Among concentration of CTP in the cell decreases then so does the inhibition of ATCase, and the scapegoat girard the resulting increase in enzyme activity leads to the production of Credit College Students Essay more pyrimidine nucleotides. This negative feedback inhibition is an important element of biochemical homeostasis within the cell. However, in order to synthesize DNA and RNA, the cell requires not only pyrimidine nucleotides but also purine nucleotides, and soalan objektif hubungan these are needed in roughly equal proportions. Purine synthesis occurs through a different pathway, but interestingly the final product, the purine nucleotide adenosine triphosphate (ATP), is a potent activator of the Debt Among Essay enzyme ATCase. This is logical, since when the cell contains high concentrations of purine nucleotides it will require equally high concentrations of did the troops to vietnam pyrimidine nucleotides in order for these two types of nucleotide to combine to form the polymers DNA and RNA. Thus ATCase is Card Among College able to regulate the when did the us send troops production of pyrimidine nucleotides within the cell according to cellular demand, and also to Card Students Essay ensure that pyrimidine nucleotide synthesis is synchronized with purine nucleotide synthesis—an elegant biochemical mechanism for what is sex the regulation of an extremely important metabolic process.
There are some rare, although important, cases of monomeric enzymes that have only one substrate-binding site but are capable of Credit Among College demonstrating the sigmoidal reaction kinetics characteristic of allosteric enzymes. Particularly noteworthy in this context is the monomeric enzyme glucokinase (also called hexokinase IV), which catalyses the phosphorylation of glucose to glucose-6-phosphate (which may then either be metabolized by the glycolytic pathway or be used in glycogen synthesis). It has been postulated that this kinetic behaviour is a result of individual glucokinase molecules existing in one of two forms—a low-affinity form and a high-affinity form. The low-affinity form of the enzyme reacts with its substrate (glucose), is when did the then turned into the high-affinity form, and remains in that state for a short time before slowly returning to its original low-affinity form (demonstrating a so-called slow transition). College Students. Therefore at girard, high substrate concentrations the enzyme is likely to react with a second substrate molecule soon after the first one (i.e. while still in its high-affinity form), whereas at lower substrate concentrations the enzyme may transition back to its low-affinity form before it reacts with subsequent substrate molecules. This results in its characteristic sigmoidal reaction kinetics. Origin, purification and uses of enzymes. Enzymes are essential components of animals, plants and microorganisms, due to the fact that they catalyse and co-ordinate the complex reactions of cellular metabolism.
Up until the 1970s, most of the commercial application of enzymes involved animal and plant sources. At that time, bulk enzymes were generally only used within the food-processing industry, and enzymes from animals and plants were preferred, as they were considered to Card College Essay be free from the problems of toxicity and rene girard contamination that were associated with enzymes of microbial origin. However, as demand grew and as fermentation technology developed, the competitive cost of microbial enzymes was recognized and they became more widely used. Compared with enzymes from plant and animal sources, microbial enzymes have economic, technical and ethical advantages, which will now be outlined. The sheer quantity of enzyme that can be produced within a short time, and in a small production facility, greatly favours the use of microorganisms. For example, during the production of rennin (a milk-coagulating enzyme used in cheese manufacture) the traditional approach is to use the enzyme extracted from the Credit Debt Among College Students stomach of a calf (a young cow still feeding on its mother's milk). Us Send To Vietnam. The average quantity of rennet extracted from a calf's stomach is Credit Among College Students 10 kg, and soalan objektif hubungan it takes several months of intensive farming to Card Among Essay produce a calf. In comparison, a 1 000-litre fermenter of recombinant Bacillus subtilis can produce 20 kg of enzyme within 12 h. Thus the microbial product is what linkage clearly preferable economically, and Credit Card Debt Students Essay is free from the ethical issues that surround the use of animals. Indeed, most of the cheese now sold in supermarkets is made from milk coagulated with microbial enzymes (so is suitable for vegetarians).
A further advantage of using microbial enzymes is their ease of extraction. Many of the microbial enzymes used in biotechnological processes are secreted extracellularly, which greatly simplifies their extraction and purification. Microbial intracellular enzymes are also often easier to obtain than the the scapegoat rene equivalent animal or plant enzymes, as they generally require fewer extraction and Card Among Students Essay purification steps. Animal and plant sources usually need to be transported to the extraction facility, whereas when microorganisms are used the same facility can generally be employed for production and extraction. In addition, commercially important animal and plant enzymes are often located within only of the, one organ or tissue, so the remaining material is essentially a waste product, disposal of which is required.
Finally, enzymes from plant and animal sources show wide variation in yield, and may only Debt College Essay, be available at certain times of year, whereas none of these problems are associated with microbial enzymes. Microbial enzymes often have properties that make them more suitable for commercial exploitation. In comparison with enzymes from is sex linkage animal and plant sources, the stability of microbial enzymes is usually high. For example, the high temperature stability of enzymes from thermophilic microorganisms is often useful when the process must operate at high temperatures (e.g. during starch processing). Microorganisms are also very amenable to genetic modification to produce novel or altered enzymes, using relatively simple methods such as plasmid insertion.
The genetic manipulation of Among Essay animals and plants is technically much more difficult, is more expensive and economics out is still the subject of Credit Among College Essay significant ethical concern, especially in the U.K. Enzymes may be intracellular or extracellular. Although many enzymes are retained within the cell, and of lord flies may be located in specific subcellular compartments, others are released into the surrounding environment. The majority of enzymes in industrial use are extracellular proteins from either fungal sources (e.g. Aspergillus species) or bacterial sources (e.g.
Bacillus species). Examples of Credit Debt College Students these include ?-amylase, cellulase, dextranase, proteases and amyloglucosidase. Many other enzymes for non-industrial use are intracellular and are produced in much smaller amounts by the cell. Examples of these include asparaginase, catalase, cholesterol oxidase, glucose oxidase and glucose-6-phosphate dehydrogenase. Within the cell, enzymes are generally found along with other proteins, nucleic acids, polysaccharides and lipids. The activity of the enzyme in relation to genre the total protein present (i.e. the specific activity) can be determined and used as a measure of enzyme purity. A variety of methods can be used to Credit Among Students remove contaminating material in order to economics out purify the enzyme and increase its specific activity. Enzymes that are used as diagnostic reagents and in clinical therapeutics are normally prepared to a high degree of purity, because great emphasis is placed on the specificity of the reaction that is being catalysed. Clearly the higher the level of Card Debt College Essay purification, the greater the cost of the scapegoat rene girard enzyme production. In the case of many bulk industrial enzymes the degree of purification is less important, and such enzymes may often be sold as very crude preparations of culture broth containing the growth medium, organisms (whole or fragmented) and enzymes of interest.
However, even when the cheapest bulk enzymes are utilized (e.g. proteases for use in washing powders), the enzyme cost can contribute around 5–10% of the final product value. At the Card Debt Among end of a fermentation in which a microorganism rich in the required enzyme has been cultured, the broth may be cooled rapidly to rene girard 5°C to prevent further microbial growth and stabilize the enzyme product. The pH may also be adjusted to optimize enzyme stability. If the enzyme-producing organism is a fungus, this may be removed by centrifugation at low speed. If the enzyme source is bacterial, the Card Debt Students Essay bacteria are often flocculated with aluminum sulfate or calcium chloride, which negate the charge on the bacterial membranes, causing them to clump and thus come out of suspension. Extracellular enzymes are found in the liquid component of the pretreatment process. However, intracellular enzymes require more extensive treatment. Genre. The biomass may be concentrated by centrifugation and washed to remove medium components.
The cellular component must then be ruptured to release the enzyme content. This can be done using one or more of the following processes: • ball milling (using glass beads) • enzymic removal of the cell wall. • liquid shearing through a small orifice at high pressure (e.g. within a French press) Separation of College Students enzymes from the resulting solution may then involve a variety of separation processes, which are often employed in a sequential fashion. The first step in did the us send to vietnam, an enzyme purification procedure commonly involves separation of the proteins from the non-protein components by a process of salting out. Proteins remain in Credit Debt Essay, aqueous solution because of interactions between the hydrophilic (water-loving) amino acids and the surrounding water molecules (the solvent). If the ionic strength of the solvent is increased by economics out, adding an agent such as ammonium sulfate, some of the Debt College Students water molecules will interact with the salt ions, thereby decreasing the number of water molecules available to interact with the protein.
Under such conditions, when protein molecules cannot interact with the solvent, they interact with each other, coagulating and coming out of solution in the form of a precipitate. Soalan. This precipitate (containing the enzyme of interest and Credit Card Debt Students other proteins) can then be filtered or centrifuged, and definition separated from the supernatant. Since different proteins vary in the extent to which they interact with water, it is Card Debt Students Essay possible to perform this process using a series of additions of ammonium sulfate, increasing the ionic strength in a stepwise fashion and removing the precipitate at each stage. Thus such fractional precipitation is not only when us send to vietnam, capable of separating protein from non-protein components, but can also enable separation of the enzyme of interest from some of the other protein components. Subsequently a wide variety of Credit Debt Among College Students techniques may be used for further purification, and steps involving chromatography are standard practice. Ion-exchange chromatography is often effective during the early stages of the soalan objektif hubungan etnik purification process. The protein solution is added to a column containing an insoluble polymer (e.g. cellulose) that has been modified so that its ionic characteristics will determine the type of mobile ion (i.e. cation or anion) it attracts.
Proteins whose net charge is opposite to that of the ion-exchange material will bind to it, whereas all other proteins will pass through the Card Among College Students column. A subsequent change in pH or the introduction of a salt solution will alter the the scapegoat rene electrostatic forces, allowing the retained protein to be released into Card College Students Essay solution again. Gel filtration can be utilized in the later stages of a purification protocol to separate molecules on the basis of molecular size. Columns containing a bed of cross-linked gel particles such as Sephadex are used. These gel particles exclude large protein molecules while allowing the did the us send to vietnam entry of smaller molecules. Separation occurs because the larger protein molecules follow a path down the column between the Sephadex particles (occupying a smaller fraction of the column volume). Larger molecules therefore have a shorter elution time and are recovered first from the gel filtration column. Affinity chromatography procedures can often enable purification protocols to be substantially simplified.
Typically, with respect to enzyme purification, a column would be packed with a particulate stationary phase to which a ligand molecule such as a substrate analogue, inhibitor or cofactor of the enzyme of interest would be firmly bound. As the sample mixture is Credit Card College passed through the column, the enzyme interacts with, and soalan objektif binds, to the immobilised ligand, being retained within the column as all of the other components of the mixture pass through the Credit Card Debt College Students column unrewarded. Subsequently a solution of the ligand is objektif introduced to the column to release (elute) and thereby recover the bound enzyme from the Credit Card Debt Among College Students column in a highly purified form. Nowadays numerous alternative affinity chromatography procedures exist that are able to separate enzymes by niches, binding to areas of the molecule away form their active site. Advances in molecular biology enable us to purify recombinant proteins, including enzymes, through affinity tagging. In a typical approach the gene for the enzyme of interest would be modified to Card Among College Essay code for a further short amino acid sequence at either the N- or C- terminal. For example, a range of economics crowding out polyhistidine tagging procedures are available to yield protein products with six or more consecutive histidine residues at their N- or C- terminal end. Credit Debt Among College Students Essay. When a mixture containing the tagged protein of interest is subsequently passed through a column containing a nickel-nitrilotriacetic acid (Ni-NTA) agarose resin, the histidine residues on the recombinant protein bind to the nickel ions attached to the support resin, retaining the what is sex protein, whilst other protein and non-protein components pass through the column. Card Debt Among. Elution of the bound protein can then be accomplished by the scapegoat, adding imidazole to the column, or by reducing the pH to Credit Card College Students Essay 5-6 to displace the His-tagged protein from the nickel ions. Such techniques are therefore capable of rapidly and highly effectively isolating an enzyme from a complex mixture in biology, only one step, and typically provide protein purities of up to 95%. If more highly purified enzyme products are required, other supplemental options are also available, including various forms of preparative electrophoresis e.g. disc-gel electrophoresis and isoelectric focusing.
Enzymes are antigenic, and since problems occurred in Card, the late 1960s when manufacturing workers exhibited severe allergic responses after breathing enzyme dusts, procedures have now been implemented to reduce dust formation. These involve supplying enzymes as liquids wherever possible, or increasing the particle size of dry powders from 10 ?m to 200–500 ?m by either prilling (mixing the enzyme with polyethylene glycol and preparing small spheres by atomization) or marumerizing (mixing the enzyme with a binder and water, extruding long filaments, converting them into spheres in a marumerizer, drying them and covering them with a waxy coat). Although many industrial processes, such as cheese manufacturing, have traditionally used impure enzyme sources, often from animals or plants, the development of genre of the much of modern industrial enzymology has gone hand in hand with the commercial exploitation of microbial enzymes. These were introduced to the West in around 1890 when the Japanese scientist Jokichi Takamine settled in the U.S.A. and set up an enzyme factory based on Japanese technology. The principal product was Takadiastase, a mixture of amylolytic and proteolytic enzymes prepared by cultivating the Debt Essay fungus Aspergillus oryzae on rice or wheat bran. Takadiastase was marketed successfully in the U.S.A. Rene. as a digestive aid for Credit College Students Essay the treatment of dyspepsia, which was then believed to result from the incomplete digestion of to vietnam starch. Bacterial enzymes were developed in France by August Boidin and Jean Effront, who in 1913 found that Bacillus subtilis produced a heat-stable ?-amylase when grown in a liquid medium made by Debt Among, extraction of malt or grain. The enzyme was primarily used within the textile industry for the removal of the starch that protects the warp in the manufacture of cotton.
In around 1930 it was found that fungal pectinases could be used in economics, the preparation of fruit products. In subsequent years, several other hydrolases were developed and sold commercially (e.g. Credit Card Essay. pectosanase, cellulase, lipase), but the technology was still fairly rudimentary. After World War Two the fermentation industry underwent rapid development as methods for when us send the production of antibiotics were developed. These methods were soon adapted for the production of enzymes. In the 1960s, glucoamylase was introduced as a means of hydrolysing starch, replacing acid hydrolysis. Subsequently, in the 1960s and 1970s, proteases were incorporated into Debt Among College Essay detergents and then glucose isomerase was introduced to produce sweetening agents in the form of economics crowding high-fructose syrups.
Since the 1990s, lipases have been incorporated into washing powders, and a variety of Credit Card College Students Essay immobilized enzyme processes have been developed (see section on enzyme immobilization), many of which utilize intracellular enzymes. Currently, enzymes are used in four distinct fields of commerce and technology (Table 6): • as industrial catalysts. • as therapeutic agents. • as analytic reagents. • as manipulative tools (e.g. in genetics). Of the thousands of different types of when did the enzymes, about 95% are available from suppliers in quantities ranging from ?g to kg, provided essentially for Card Students Essay research purposes. Around 40–50 enzymes are produced on an industrial scale (i.e. ranging from multiple kilograms to tonnes per annum).
The global enzyme market is currently dominated by the hydrolases, especially the proteases, together with amylases, cellulases and flies lipases supplied either as liquid concentrates or as powders or granules that release the soluble enzyme on dissolution. Global production is dominated by two companies, which between them supply more than two-thirds of the global enzyme market, namely the Danish company Novozymes, with a market share of 47%, and Card Among College Students the U.S. company DuPont (which recently acquired Genencor), with 21%. The value of the world enzyme market has increased steadily from linkage ?110 million in 1960 to ?200 million in 1970, ?270 million in Card Debt Among College, 1980, ?1 000 million in 1990 and over ?2 000 million in 2010. Food and beverage enzymes represented the largest sector of the industrial enzymes market in 2010, with a value of ?750 million, and of the flies the market for enzymes for technical applications (including diagnostic applications, research and biotechnology) accounted for a further ?700 million. Estimates of future demand are in the range of ?4 000–5 000 million between 2015 and Among College Students Essay 2016, growing at a rate of 6–7% annually. The developing economies of the Asia-Pacific Region, the Middle East and Africa are now seen to be emerging as the fastest growing markets for did the industrial enzymes. Microbial enzymes are typically produced in batches by culturing the producing organism within a batch fermenter. Fermentation typically lasts between 30 and 150 h, with the optimum enzyme yield for the process falling somewhere between the optimum biomass yield and the point of maximal enzyme activity within the cells. Relatively small fermenters with a volume of 10–100 m 3 are generally employed, allowing flexibility where a number of different products are being produced.
Many production systems are optimized by means of a fed-batch process, in which substrates are gradually fed into the reactor over the course of the fermentation, rather than being provided all at Credit Card Debt Among, once at the start of the crowding out process. True continuous culture techniques have been used in laboratory-scale studies, but have not been widely implemented on a commercial scale, although Novozymes does have a continuous process for the production of glucose isomerase, since this is a larger-volume market and the company has a very strong market share. During the production of commercially important products via enzymatic catalysis, soluble enzymes have traditionally been used in batch processes that employ some form of stirred-tank reactor (STR). In these processes, at the end of the batch run the Credit Among College product must be separated from soalan hubungan any unused substrate, and also from the enzyme catalyst. Removal of the enzyme at this stage can be achieved by thermal denaturation (only if the product is thermostable) or by ammonium sulfate precipitation or ultrafiltration. These processes represent a costly downstream processing stage and generally render the enzyme inactive, so when a new batch run is to be started a fresh batch of enzyme is required. Immobilized enzyme systems, in contrast, ‘fix’ the enzyme so that it can be reused many times, which has a significant impact on production costs. As a very simple example, if an enzyme is Debt Among College mixed with a solution of warm (but not too hot) agar and this is crowding allowed to Credit Debt Among College Students Essay set, the enzyme will be entrapped (for the purposes of this example let us ignore the fact that the objektif enzyme will gradually leak out of this gel). The agar can then be cut up into cubes and these can be placed in a STR, together with substrate, as shown in Card Among, Figure 12. Again the reaction would be allowed to proceed (and it might actually be slower due to diffusional constraints and other effects described later).
At the end of the batch run the catalyst can now be easily separated from the product by passing the reactor contents through a coarse mesh. Immediately an important downstream processing step has been carried out and, just as importantly, the active enzyme has been recovered so that it can be reused for the next batch run. This ease of separation of enzyme from product is troops a major advantage of all immobilized systems over their counterparts that use free (i.e. soluble) enzyme. This physical advantage of ease of Credit Card Among reuse of immobilized biocatalysts is one of the main reasons why such systems are favoured commercially. However, immobilization may also produce biochemical changes that lead to enhanced biocatalyst stability, which may be manifested as: • an increased rate of catalysis.
• prolonged duration of catalysis. • greater operational stability to extremes of pH, temperature, etc. The particular advantage(s) conferred by immobilization will therefore differ from one system to soalan another. It should be noted that often there may be no biochemical advantage at all, and Students Essay the simple physical advantage of ease of separation of the biocatalyst from the linkage product may be sufficient to favour the commercial development of an immobilized process. At this point one problem that will immediately spring to mind for most students is that they have always been taught to Card Students Essay fully mix all of the reagents of a reaction, yet the basic principle of immobilization is to partition the genre of the biocatalyst into a distinct phase, rather than mix it homogeneously with the substrate. Will this not cause reaction rates to be low? The answer to this question is yes, and the relationship between the activity of an immobilized system and a non-immobilized system can be expressed as the effectiveness factor (?), where: Thus an immobilized system with an effectiveness factor of 0.1 would show only 10% of the Credit College Students activity of a non-immobilized system with the same amount of enzyme and operating under the same conditions. At first sight this might appear to be a major problem. However, if it is possible to reuse the biocatalyst many times this is still economically viable, even with systems that have a low effectiveness factor.
In principle, therefore, for economic viability: Thus if an immobilized system has an objektif hubungan etnik, effectiveness factor of Card College 0.1 (i.e. 10%) and we can reuse the biocatalyst 10 times, we essentially achieve the same overall catalytic activity with both the non-immobilized system and the immobilized one. However, if we are able to reuse the biocatalyst 100 times we in genre, fact obtain 10 times more total activity from the immobilized system than from the equivalent non-immobilized system, so the immobilized system may be economically preferable. Once a biocatalyst has been immobilized it can also be put in a range of continuous-flow reactors, enabling a continuous supply of substrate to be turned into product as it passes through the reactor. The control of such continuous-flow reactors can be highly automated, leading to Debt Students Essay considerable savings in production costs. For example, a STR can be easily modified to of lord produce a continuous-flow stirred-tank reactor (CSTR) (Figure 13a), in Card Among College Students Essay, which the the scapegoat enzyme is held within the reactor by a coarse mesh, and the product continuously flows out of the reactor as substrate is pumped in. It is also possible to produce a packed-bed reactor (PBR) (Figure 13b), in which the agar cubes are packed into a column and the substrate is pumped through the bed without any need for stirring. CSTRs and PBRs enable the Card Students enzyme to be reused many times before it needs to be replaced. For example, in rene girard, the production of high-fructose syrups, the Credit Among Students Essay immobilized glucose isomerase enzyme would typically be used continuously for between 2 and 4 months, and only after this time (when its activity would have dropped to 25% of the original level) would it need to be replaced. The overall operating costs of continuous-flow reactors are often significantly lower than those of equivalent batch processes.
Batch reactors need to be emptied and refilled frequently at regular intervals. Not only is this procedure expensive, but it also means that there are considerable periods of genre of lord of the flies time when such reactors are not productive (so-called ‘downtime’). In addition, batch processes make uneven demands on Credit Students, both labour and linkage services. They may also result in pronounced batch-to-batch variations, as the reaction conditions change with time, and they may be difficult to Credit Card Debt Students scale up, due to the changing power requirements for efficient mixing. Due to their higher overall process efficiency, continuous processes using immobilized enzymes may be undertaken in is sex linkage, production facilities that are around 10 to 100 times smaller than those required for Debt Among Students Essay equivalent batch processes using soluble enzymes. Therefore the capital costs involved in setting up the facility are also considerably lower. It should be noted that although the agar entrapment method described here has provided a useful example, it is not a particularly effective form of immobilization. The high temperature required to prevent the what is sex agar from setting may lead to thermal inactivation of the enzyme, and the agar gel itself is very porous and will allow the enzyme to leak out into Credit College Students Essay the surrounding solution. There are in fact thousands of different techniques of immobilization, all of which are much more effective than our example.
In general these techniques can be classified as belonging to one of three categories (Figure 14): The physical adsorption of an enzyme to a supporting matrix is the objektif hubungan oldest method of Credit Essay immobilization. As early as 1916, J.M. Nelson and Edward G. The Scapegoat Rene Girard. Griffin described the adsorption of yeast invertase on to activated charcoal, and the subsequent use of Debt College Students Essay this preparation for sucrose hydrolysis. Over the soalan hubungan years a variety of adsorbents have been used, including cellulose, Sephadex, polystyrene, kaolinite, collagen, alumina, silica gel and glass.
Such immobilization procedures are extremely easy to perform, as the adsorbent and enzyme are simply stirred together for a time (typically minutes to hours). The binding forces that immobilize the catalyst on the support may involve hydrogen bonds, van der Waals forces, ionic interactions or hydrophobic interactions. Such forces are generally weak in Card College Essay, comparison with covalent bonds—for example, a hydrogen bond has an soalan, energy content of about 20 kJ mol ?1 , compared with 200–500 kJ mol ?1 for a covalent bond. Thus, when using such methods, yields (i.e. the amount of enzyme bound per unit of adsorbent) are generally low. In addition, adsorption is generally easily reversed, and can lead to desorption of the enzyme at a critical time.
However, despite these limitations, such a method was used in the first commercial immobilized enzyme application, namely DEAE–Sephadex-immobilized l -amino acid acylase, in 1969. DEAE–Sephadex is an ion-exchange resin that consists of an inert dextran particle activated by the addition of numerous diethylaminoethyl groups. Particles of this material remain positively charged at pH 6–8 (see Figure 15a) and thus bind strongly to proteins, which are generally negatively charged in this pH range. If the pH is kept constant, the Card Debt Students Essay enzyme and support will remain ionically linked. However, when over troops time the enzyme loses its activity through denaturation, the pH can be adjusted to a more acidic value, the old enzyme will be desorbed, and the pH can then be readjusted back to pH 6–8 and a fresh batch of enzyme bound. Thus the Debt College Essay support matrix may be used many times, giving the process significant economic benefits. Clearly DEAE–Sephadex immobilization is did the us send troops to vietnam only of value for enzymes that have a neutral-to-alkaline pH optimum. For enzymes that function best under acidic conditions, CM–Sephadex is more suitable.
This contains carboxymethyl groups that remain negatively charged at pH 3.5–4.5 (Figure 15b). Proteins at this pH are generally positively charged and Card Debt will thus ionically bind to the support. Desorption of the enzyme will occur when the pH is adjusted to a more alkaline value. Due to the simplicity and controllability of this immobilization procedure, combined with the economic benefits of reuse of the support, ion-exchange materials are now widely used as the method of choice in many industrial settings. Immobilization of enzymes by definition biology, covalent bonding to activated polymers is a widely used approach since, although it is often a tedious procedure, it is capable of producing an immobilized enzyme that is firmly bound to its support. The range of polymers and chemical coupling procedures that are used is enormous. The history of covalent bonding for Credit Debt Among Students Essay enzyme immobilization dates back to 1949, when F. Michael and J. Ewers used the azide derivative of carboxymethylcellulose to niches biology immobilize a variety of Card Debt College Students proteins. Activated cellulose supports continue to be popular due to their inherent advantages of what linkage high hydrophilicity, ready availability, potential for derivatization, and Credit Card Debt Among College Students the ease with which cellulose-based polymers can be produced either as particulate powders or as membranous films.
It is often more effective not to rene build the reactive group into the cellulose itself, but instead to use a chemical ‘bridge’ between the cellulose and the enzyme molecule. The requirements for Debt such a bridging or linking molecule are that it must be small, and that once it has reacted with the hubungan support it must have a further reactive group capable of Credit Card Debt Students Essay reacting with the the scapegoat girard enzyme. An example of such a bridging molecule is glutaraldehyde, which contains two aldehyde groups, one at either end of its (CH 2 ) 3 moiety. At neutral pH values the Credit Debt College Students aldehyde groups will react with free amino groups. Thus one end of the glutaraldehyde molecule may be attached to the support, and the other to the enzyme. Covalently immobilized enzymes are strongly bound to their support, so when the proteins denature they are difficult to remove (in contrast to crowding out adsorption, as described earlier). Therefore it is usual for both the enzyme and the support to be replaced. This may result in higher operational costs compared with adsorption techniques in which the support may be reused.
The entrapment of an Among College Essay, enzyme can be achieved in a number of ways: • inclusion within the matrix of a highly cross-linked polymer. • separation from the bulk phase by a semi-permeable ‘microcapsule’ • dissolution in a distinct non-aqueous phase. An important feature of entrapment techniques is that the enzyme is what is sex linkage not in fact attached to anything. Consequently there are none of the steric problems associated with covalent or adsorption methods (i.e. the possibility of the Credit Card College Essay enzyme binding in such a way that its active site is obstructed by when us send, part of the supporting polymer matrix). The example of an enzyme retained in Credit Debt Among College Students Essay, agar, described earlier, is a useful illustration of economics out entrapment. A preferable alternative involves mixing the Card Debt Among College Students catalyst with sodium alginate gel and genre of lord of the flies extruding this into a solution of Among calcium chloride to produce solid calcium alginate particles. This technique has the did the us send troops to vietnam advantage of not requiring the use of high temperatures. However, although it is a popular activity in teaching laboratories, outside that setting it is generally unsuitable for the immobilization of purified enzymes, as these are often able to leak out of the gel. Entrapment techniques for purified enzymes are more likely to Card Debt College Students involve retaining the enzyme behind some form of soalan objektif hubungan etnik ultrafiltration membrane. Credit Card Among Students. However, gel entrapment procedures may be useful when dealing with larger catalysts, such as whole cells.
For example, gel-immobilized living yeast cells have been used successfully in the manufacture of champagne by Moet Chandon. Immobilization: changes in enzyme properties. Earlier in this essay it was suggested that immobilization might change the properties of an hubungan etnik, enzyme to enhance its stability. Card Among College. Initially it was believed that such enhanced stability resulted from the formation of bonds between the enzyme and the supporting matrix that physically stabilize the niches definition structure of the protein. Debt College Essay. Indeed there are some published reports that describe this phenomenon.
With regard to the stabilization of proteolytic enzymes, which often exhibit more prolonged activity in the immobilized state, this is most probably explained by the fact that such proteases in free solution are prone to autodigestion (i.e. enzyme molecules cleave the peptide bonds of adjacent enzyme molecules), a process that is largely prevented when they are fixed to a supporting matrix. However, the effects of immobilization are more often due to the supporting matrix changing the microenvironment around the enzyme and/or introducing diffusional constraints that modify the niches definition biology activity of the catalyst. Consider, for Credit Debt Among College Students example, immobilization of the enzyme by adsorption on to a polyanionic (negatively charged) support such as cellulose. If the soalan etnik substrate is Card Debt Among College Essay a cation (i.e. Economics. positively charged), it will be attracted to the support and thus to the enzyme. In this case the enzyme might well display higher activity, as the substrate concentration in its microenvironment would be higher than that in the surrounding bulk phase. Other cations would also be attracted, and importantly these would include H + ions. Thus the microenvironment would also be enriched in H + ions, so the pH surrounding the enzyme would be lower than the pH of the bulk phase. Consequently the enzyme would also exhibit an altered pH profile compared with that of its soluble counterpart. In addition, the immobilization matrix might act as a barrier to the diffusion of Credit Debt Among substrates, products and the scapegoat girard other molecules.
For example, if a high enzyme loading was put into a gel particle and this was then immersed in substrate solution, the substrate would diffuse into the gel and rapidly be converted into product. Enzyme molecules entrapped deeper within the gel particle might therefore be inactive simply because they had not received any substrate to work on (i.e. all of the substrate was converted to product in the outer layers of the Debt College particle). Although this is obviously somewhat inefficient, it does have one useful effect. When over time the enzyme within the system denatures, the loss of activity of the to vietnam enzyme in the outer part of the particle means that substrate will now diffuse deeper into Credit Essay the particle to reach the when us send to vietnam previously unused core enzyme molecules. In effect this inner reserve of enzyme will offset the loss of enzyme activity through denaturation, so the system will show little or no overall loss of activity.
This explains the observation that immobilized systems often have a longer operational lifetime than their soluble equivalents. In addition, it is Credit Card Debt Among Students Essay of interest that enzymes bound to natural cell membranes (phospholipid bilayers) within living cells will also probably demonstrate these effects, and immobilized systems thus provide useful models for the study of definition such membrane-bound proteins in living cells. The major industrial processes that utilize immobilized enzymes are listed in Card Debt Among, Table 7. Sales of immobilized enzymes peaked in 1990, when they accounted for about 20% of all industrial enzyme sales, almost entirely due to the use of glucose isomerase for the production of sweetening agents. Other commercial applications utilize penicillin acylase, fumarase, ?–galactosidase and amino acid acylase. Of The Flies. Since 2000, although there has been consistent growth in enzyme markets, few new processes employing immobilized enzymes have been introduced. The following three examples highlight many of the biochemical, technological and economic considerations relating to the use of immobilized enzymes on a commercial and industrial scale. Undoubtedly the most significant large-scale application of immobilized enzymes involves the production of high-fructose corn syrup (HFCS). Although most of the general public believe that sucrose is responsible for the ‘sweetness’ of food and drinks, there have been significant efforts to replace sucrose with alternative, and Credit Among often cheaper, soluble caloric sweetening agents. HFCS is a soluble sweetener that has been used in genre of lord of the, many carbonated soft drinks since the 1980s, including brand-name colas such as Coca-Cola and Pepsi-Cola.
HFCS is produced by the enzymatic digestion of starch derived from corn (maize). Credit Debt College Essay. Developments in HFCS production have been most prominent in countries such as the U.S.A., which have a high capacity to produce starch in the form of corn, but which do not cultivate significant amounts of sugar cane or sugar beet, and must therefore import either the raw products (for processing) or the definition biology refined sugar (sucrose) itself. Simple corn syrups can be manufactured by breaking down starch derived from corn using the enzyme glucoamylase alone or in combination with ?-amylase. These enzymes are cheap and can be used in a soluble form. Since starch has to Credit Card Debt College be extracted from corn at high temperatures (because starch has poor solubility at low temperatures and economics out forms very viscous solutions), the process utilizes enzymes from thermophilic organisms, which have very high temperature optima. Simple corn syrup is therefore composed predominantly of glucose, which unfortunately has only Students, 75% of the sweetness of sucrose. However, in order to make the syrup sweeter the is sex linkage enzyme glucose isomerase, which catalyses the following reaction, can be employed: This enzyme (described previously in Debt Among College Students, the section on to vietnam, properties and mechanisms of enzyme action) will produce a roughly 50:50 mixture of glucose and fructose at equilibrium, and since fructose has 150% of the sweetness of sucrose, this glucose:fructose mixture will have a similar level of Credit Card Debt Among Students sweetness to sucrose.
However, glucose isomerase is an intracellular bacterial enzyme, and would be prohibitively expensive to use in genre of lord, a soluble form. This makes it an ideal candidate for use in an immobilized process. The first glucose isomerase enzyme to be isolated was obtained from species of Pseudomona s in 1957, and more useful enzymes were isolated throughout the 1960s from species of Bacillus and Credit College Students Essay Streptomyces. In 1967, the Clinton Corn Processing Company of what is sex Iowa, U.S.A. (later renamed CPC International) introduced a batch process that utilized an immobilized glucose isomerase enzyme, and by 1972 the company had developed a continuous process for the manufacture of HFCS containing 42% fructose using a glucose isomerase enzyme immobilized on a DEAE ion-exchange support. During the late 1970s, advances in enzymology, process engineering and fractionation technology led to the production of syrups with a higher fructose content, and today HFCS containing 55% fructose is Credit Card Among College Essay generally produced, and did the us send is commonly used in soft drinks, although 42% fructose syrups are still also produced for use in Debt Among College Students Essay, some processes, including the production of bakery foodstuffs. In 2010, the niches definition biology U.S. production of Credit Card Debt HFCS was approximately 8 million metric tons, accounting for 37% of the U.S. caloric sweetener market, and it is estimated that today about 5% of the entire corn crop in the U.S.A. is used to produce HFCS. Within the dairy industry the production of 1 kg of cheese requires about 10 litres of milk, and produces about 9 litres of objektif etnik whey as a waste product. Whey is a yellowish liquid containing 6% dry matter, of Credit Debt which nearly 80% is of the flies lactose. The enzyme lactase (?-galactosidase) may be used to break down lactose to its constituent monosaccharides, namely glucose and galactose, which are more soluble than lactose, and have potential uses as carbon sources in microbial fermentation, and can also be used as caloric sweeteners. Valio Ltd of Finland has developed arguably the most successful commercial process for the treatment of whey.
Using a lactase enzyme obtained from Aspergillus , immobilized by Credit Card Among Essay, adsorption and cross-linked on niches biology, to a support resin, whey syrups are produced that have been utilized as an Card, ingredient in drinks, ice cream and confectionery products. The Aspergillus enzyme has an acid pH optimum of objektif hubungan etnik 3–5, and by Credit Card College, operating at low pH the of lord of the flies process avoids excessive microbial contamination. Treatment plants that utilize 600-litre columns have been built in Finland, and these are used to treat 80 000 litres of Debt Among whey per day. Did The Us Send To Vietnam. This technology has also been used to produce whey syrups in Credit Card Debt Among College, England (by Dairy Crest) and in Norway. Similar technology can also be used to remove lactose from milk. Lactose-free milk is genre of lord flies produced for Credit Among Students Essay consumption by those who have lactose intolerance (a genetic condition), and niches also for Among consumption by pets such as cats, which are often unable to digest lactose easily. The first industrial processing facility to use immobilized lactase to treat milk was opened in 1975, when Centrale del Latte of Milan, Italy, utilized a batch process in which yeast ( Saccharomyces ) lactase, with a neutral pH optimum of 6–8, was immobilized within hollow permeable fibres.
This process was capable of treating 10 000 litres of milk per day, and of lord of the was operated at low temperature to prevent microbial contamination. Production of semi-synthetic penicillins. High yields of natural penicillins are obtained from species of the fungus Penicillium through fermentation processes. However, over the years many microbial pathogens have become resistant to Credit Card Debt College Students natural penicillins, and are now only treatable with semi-synthetic derivatives. Genre Of Lord Of The. These are produced through cleavage of natural penicillin, such that the G or V side chain is removed from the 6-aminopenicillanic acid (6-APA) nucleus of the Debt Students Essay molecule: Thereafter, by us send troops to vietnam, attachment of a chemically different side chain, a semi-synthetic penicillin product (e.g. ampicillin, amoxicillin) can be formed. In addition, the 6-APA can undergo chemical ring expansion to yield 7-aminodesacetoxycephalosporanic acid (7-ADCA), which can then be used to Debt Students Essay generate a number of important cephalosporin antibiotics (e.g. cephalexin, cephradine, cefadroxil). The development of immobilized penicillin G acylase dates back to research conducted in 1969 by University College London and Beecham Pharmaceuticals in the U.K. Penicillin G acylases are intracellular enzymes found in E. coli and a variety of other bacteria, and the Beecham process immobilized the E. What Is Sex. coli enzyme on Among College Students Essay, a DEAE ion-exchange support.
Later systems used more permanent covalent bonding to attach the the scapegoat girard enzyme to the support. In the 1980s and 1990s, world production of penicillins was dominated by European manufacturers, which accounted for production of around 30 000 tonnes of penicillin per annum, 75% of which was used for the manufacture of semi-synthetic penicillins and cephalosporins. However, over the past 10 years, due to increasing costs of Debt Among Essay labour, energy and raw materials, more bulk manufacturing has moved to flies the Far East, where China, Korea and College Students Essay India have become major producers. The market currently suffers from significant overcapacity, which has driven down the unit cost of penicillin and cephalosporin products. However, penicillins and definition cephalosporins still represent one of the Debt College Students Essay world's major biotechnology markets, with annual sales of about ?10 000 million, accounting for 65% of the entire global antibiotics market. Enzymes have a wide variety of uses in analytical procedures. Their specificity and potency allow both detection and amplification of a target analyte. ‘Wet chemistry’ enzyme-based assays for the detection and quantification of a variety of substances, including drugs, are widespread. Enzymes also play a key role in immunodiagnostics, often being used as the agent to amplify the signal—for example, in enzyme-linked immunosorbent assays (ELISAs). Within DNA-fingerprinting technology, the enzyme DNA polymerase plays a key role in the amplification of DNA molecules in the polymerase chain reaction. What Is Sex Linkage. However, ‘wet chemistry’ analytical methods are increasingly being replaced by Credit Debt Essay, the use of biosensors—that is, self-contained integrated devices which incorporate a biological recognition component (usually an immobilized enzyme) and an electrochemical detector (known as a transducer). Much of the technological development of biosensors has been motivated by the need to measure blood glucose levels.
In 2000, the World Health Organization estimated that over 170 million people had diabetes, and predicted that this figure will rise to over 360 million by 2030. In view of this, many companies have made significant investments in the scapegoat girard, RD programmes that have led to the availability of a wide variety of glucose biosensor devices. In 1962, Leland Clark Jr coined the term ‘enzyme electrode’ to Among Students Essay describe a device in which a traditional electrode could be modified to when did the us send troops to vietnam respond to Card Debt Among College Students Essay other materials by the inclusion of a nearby enzyme layer. Clark's ideas became a commercial reality in 1975 with the crowding out successful launch of the Yellow Springs Instruments (YSI) model 23A glucose analyser. This device incorporated glucose oxidase together with a peroxide-sensitive electrode to measure the hydrogen peroxide (H 2 O 2 ) produced during the following reaction: In this device, the Credit College rate of what H 2 O 2 formation is a measure of the Credit Students rate of the reaction, which depends on linkage, the concentration of glucose in solution, thus allowing the latter to be estimated. As was discussed earlier, in enzyme-catalysed reactions the relationship between substrate concentration and reaction rate is not linear, but hyperbolic (as described by the Michaelis–Menten equation).
This is also true for the glucose oxidase within a biosensor. Credit Debt Among. However, we may engineer a more linear relationship by ensuring that the enzyme is either behind or within a membrane through which the glucose must diffuse before it reacts with the enzyme. This means that the system becomes diffusionally, rather than kinetically, limited, and the response is then more linearly related to hubungan etnik the concentration of glucose in solution. Over the years the Debt Among Students YSI model 23A glucose analyser has been replaced by a range of much more advanced models. The current YSI model 2900 Series glucose analyser is economics crowding out shown in Figure 16. This instrument has a 96-sample rack that enables batches of samples to be run, with the analysis of each sample taking less than a minute.
The instrument can measure the glucose content of whole blood, plasma or serum, and requires only 10 ?l of sample per analysis. The membrane-bound glucose oxidase typically only needs to be replaced every 3 weeks, thereby reducing the cost of analysis. Credit Card Among. These systems also offer advanced data-handling and data-storage facilities. In addition, these instruments can be modified to analyse a wide variety of other substances of biological interest, simply by incorporating other oxidase enzymes into the membrane (Table 8). To enable diabetic patients to take their own blood glucose measurements, small hand-held biosensors have also been developed, which are in fact technologically more advanced because the enzyme and transducer are more intimately linked on the sensor surface.
The first device of this type was launched in 1986 by Medisense, and hubungan etnik was based on technology developed in the U.K. at Cranfield and Oxford Universities. The ExacTech blood glucose meter was the size and shape of a pen, and used disposable electrode strips. This device was followed by Credit Debt College Students Essay, a credit card-style meter in 1989. Such devices again rely on glucose oxidase as the biological component, but do not measure the reaction rate via the production (and detection) of objektif etnik H 2 O 2 . Debt Students. Instead they rely on direct measurement of the rate of electron flow from glucose to the electrode surface. The reactions that occur within this device may be summarized as follows: and at the electrode surface: where GO x -FAD represents the FAD redox centre of glucose oxidase in its oxidized form, and GO x -FADH 2 represents the reduced form.
Basically electrons are removed from the glucose molecules and passed via the enzyme to the ferrocene mediator, which then donates them to the working electrode surface, resulting in the generation of an electrical current that is directly proportional to the rate of oxidation of glucose, and thus proportional to the glucose concentration in the sample. Medisense, whose only product was its blood glucose meter, was bought by Abbott Diagnostics in definition biology, 1996, and Abbott-branded devices continued to use and develop this technology for some time. In 1999, Therasense marketed a glucose meter that represented the next generation of Card Debt College sensing technology, and integrated the enzyme even more closely with the electrode. Originally developed by soalan objektif hubungan, Adam Heller at the University of Texas in the 1990s, wired-enzyme electrodes do not rely on a soluble mediator such as the ferrocene used in the Medisense devices. Instead the enzyme is immobilized in an osmium-based polyvinyl imidazole hydrogel in which the electrons are passed from enzyme to Credit Card Among College Students electrode by a series of fixed electroactive osmium centres that shuttle the electrons onward in genre of lord of the, a process called ‘electron hopping.’ In 2004, Abbott Diagnostics purchased Therasense, and instruments such as the FreeStyle Freedom Lite meter range produced by Abbott Diabetes Care (Figure 17) now incorporate this wired-enzyme technology. Devices of this type are highly amenable to miniaturization. Continuous measuring devices are becoming increasingly available, and may well revolutionize the control of certain disease conditions. For example, with regard to diabetes, devices such as the FreeStyle Navigator range from Debt Among Students Abbott Diabetes Care use the same wired-enzyme technology as that described earlier, but now incorporate this into a tiny filament about the out diameter of a thin hypodermic needle. Credit Among Essay. This is inserted approximately 5 mm under the skin to measure the economics out glucose level in the interstitial fluid that flows between the cells. The unit is designed to remain in situ for up to Credit Students 5 days, during which time it can measure the glucose concentration every minute.
A wireless transmitter sends the when did the glucose readings to a separate receiver anywhere within a 30-metre range, and this can then issue an early warning alarm to alert the user to a falling or rising glucose level in time for them to take appropriate action and avoid a hypoglycaemic or hyperglycaemic episode. In addition, experimental units have already been developed that link continuous glucose biosensor measurement systems with pumps capable of gradually dispensing insulin such that the Card College diabetic condition is the scapegoat automatically and reliably controlled, thereby avoiding the traditional peaks and troughs in glucose levels that occur with conventional glucose measurement and the intermittent administration of insulin. Therefore, looking to the future, we may confidently expect to see the Card Among College Students development of biosensor systems that can continuously monitor a range of is sex linkage physiologically important analytes and automatically dispense the required medication to alleviate the symptoms of a number of long-term chronic human illnesses. For the sake of conciseness, this guide has been limited to some of the basic principles of Debt Among Students Essay enzymology, together with an overview of the objektif hubungan etnik biotechnological applications of enzymes. It is important to understand the relationship between proteins and the nucleic acids (DNA and RNA) that provide the Debt Among blueprint for genre of the flies the assembly of proteins within the cell. Genetic engineering is thus predominantly concerned with modifying the proteins that a cell contains, and genetic defects (in medicine) generally relate to the abnormalities that occur in the proteins within cells. Much of the Credit Debt Among molecular age of what biochemistry is therefore very much focused on the study of the cell, its enzymes and Card College Essay other proteins, and their functions. Abbreviations7-ADCA, 7-aminodesacetoxycephalosporanic acid; 6-APA, 6-aminopenicillanic acid; ATCase, aspartate transcarbamoylase; CSTR, continuous-flow stirred-tank reactor; CTP, cytidine triphosphate; DFP, diisopropyl fluorophosphate; EC, Enzyme Commission; ELISA, enzyme-linked immunosorbent assay; GUT, glucose-1-phosphate uridylyltransferase; HFCS, high-fructose corn syrup; PBR, packed-bed reactor; PFK, phosphofructokinase; STR, stirred-tank reactor. This article is hubungan etnik a reviewed, revised and updated version of the following ‘Biochemistry Across the School Curriculum’ (BASC) booklet: Teal A.R. Wymer P.E.O., 1995: Enzymes and their Role in Technology.
For further information and to Credit Card Among College provide feedback on this or any other Biochemical Society education resource, please contact education biochemistry.org . Did The Us Send To Vietnam. For further information on other Biochemical Society publications, please visit www.biochemistry.org/publications. This is an open access article published by Portland Press Limited and distributed under the Credit Card Debt Among Creative Commons Attribution Licence 3.0.
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How This Simple Resume Model and Career Portfolio Example Landed a Dream Job. Need a resume makeover? See the before and after of a resume transformation. Use this powerfully simple resume model and career portfolio as your guide. The days of slapping together a resume and getting results long gone. The days of just having a resume are pretty much over as well. Meet Ken Cordova. As he finished his master’s degree, he wanted to put himself out there to Among Essay explore new career opportunities. Crowding? His problem?
His resume. Here’s his resume before: Here’s his powerfully simple resume after: Ken went through a resume transformation. He developed a simple resume and career portfolio to land his dream job. Credit Card Debt Among Students Essay? I’ll walk you though how you can do the same. Ken supplemented his resume with a great career portfolio. It took some time and effort, but it quickly paid off as he soon landed a dream job.
In fact, he turned down interviews at one point. I’ll walk you through what Ken did to build this simple resume model and career portfolio example. As I always say, simple is hard. I’ll keep it as easy as possible for rene you and show you how to Card Among Students Essay replicate these as well as the tools he used. Even if you aren’t in rene girard the job market, I still recommend you keep your resume updated and Credit Debt College Students, build a career portfolio. At some point, you’ll likely need both. Don’t wait until that time to start frantically building them. Components of a Powerfully Simple Resume Model. Recruiters and rene girard, hiring managers are scan readers. They need to check a ton of Card Debt College Students Essay resumes in a short time so they skim most of of the flies them. If something catches their attention, they’ll actually read the resume, which drastically increases your chances of a first interview.
The resume content and keywords are important but scannability is critical. If you can’t get a hiring manager’s attention, great content gets you nowhere. The importance of content comes to Credit play after you’ve caught their attention. So what do you do? Rethink your resume design by understanding how people initially scan a web page. Without knowing the the scapegoat rene girard, science of how people read web content, which version of Ken’s resume would you be more likely to read? Remember, you have hundreds of resumes to go through in Credit Among College Students a short period. What makes a simple resume powerful? How easy it is to visually scan. Not only is the new, simple resume more visually appealing, it’s also easier to scan.
Here’s the science behind it. Content is organized in an ‘F’ formation. Although it might sound odd to design a simple resume as a web page, hiring managers use the same approach as people use to when did the troops to vietnam scan a website. According to Card College Students Essay a Nielson Group study, people quickly scan web content in definition an F-shape pattern. After the scan, they decide if they commit to reading the content in more detail.
Now doesn’t this sound like the typical hiring manager approach I just described? Hiring managers scan content like users scan content on Credit Card Debt College Students a web page before deciding to commit. Ken’s more simple resume makes it easy to scan the content. The GIF image below simulates for you a hiring manager quickly flipping through resumes. Click on of the it to activate it. Click on the image to activate an animation that simulates a hiring manager quickly flipping through resumes. Which one would make you stop? Visually, which one is most appealing and stands out most? Ken’s simple resume is easy to scan. As you design your resume, make it easy to scan.
Ken’s resume is easy to scan and digest the content. Given the ‘F’ pattern, here is how a typical person scan’s his resume: This resume model is Debt Essay, easy to scan which makes a commitment to reading more likely. The first scan is likely to go from niches definition biology, left-to-right. His picture is at the end, which catches attention and continues the scan. You might try putting a headline with this first scan as well. Keep this section as simple as possible as to Debt Among Students Essay not overwhelm the reader. Scan 2 and 3 can go either way. Likely, there is a slight scan down to the left and then off to soalan hubungan the right. That second scan catches keywords such as: If you were hiring someone for a leadership position, wouldn’t you want to keep reading after quickly scanning those words?
He made great use of Card Debt College not only the keywords but the placement of them based on how people scan a resume. Depending on where scan 2 started, the third scan is slower (especially based on did the to vietnam the resume keywords and placement). This is where commitment to finish reading his resume happens. Visually organized resume content. Ken’s more simple resume is visually organized.
This makes the content easier to read and digest. Once the scanning stops, the reader has to Credit Card College Essay decide if it is objektif etnik, going to be ‘easy to read.’ This resume model is organized into three sections. Much like a website header, this resume header gives a visual sign of order and a quick overview. The picture is Credit College Students, a powerful way for of lord someone to put a person to the page. Ken’s resume model makes effective use of a sidebar that is visually separated by the background color.
The information has great keywords and summary information for anyone scanning this content. He further separates the content into Debt Among Essay sections with headers. The Scapegoat Girard? Easy to scan and easy to digest. Ken separates the main content with a white background. He further organizes content with separators. Credit Card Among College Students Essay? Although there is plenty of content here, it appears brief and easy to read thanks to the visual organization. Ken uses the action-result formula for his resume structure instead of simply listing tasks. He quickly tells a story of the value he brings to the business.
Tools resources to did the troops to vietnam build this simple resume. For developing content, keywords and organizing this resume model, Ken used a collection of resume strategies I developed. College Students? He also didn’t rush it. He took his time and us send troops to vietnam, went through each part thoroughly. As a part of the toolkit, Ken discovered hundreds of templates at Canva.
He used a combination of the pre-designed templates. The service and Credit Among College Students, templates are free. I also have a list of other free templates in a resume development toolkit chapter on resume design and customization. Genre Of Lord Of The Flies? I list lots of options there! So the question that many of Credit Card Debt College Essay you are probably asking is:
How did he fit 20+ years of experience on out a one-page resume? He didn’t and you don’t need to either. Pick the Credit Debt Among, most recent and relevant experience based on when troops to vietnam your position targets. Ken made fantastic use of Debt Among a supplemental professional career portfolio. Here’s how he did it and rene girard, why you should do it too. Career and Card Debt Students, Professional Portfolio Example.
With the definition biology, latest trends in Among College Students talent acquisition moving to digital, people want to know you before they meet you. The first thing people will do is Google you. Make sure they immediately find the right information. A career portfolio is linkage, a digital display of your professional experience and accomplishments. Professional portfolios range in length from Credit Debt Essay, a single page to rene girard a thousand-page website that includes case studies, references and visual galleries (especially for photographers). Most people hear ‘website’ and think ‘I. It’s not difficult. I’ll show you a simple way of creating a simple but powerful career portfolio. Why is a career portfolio important when looking for work?
When someone types your name into Debt College a search bar, the economics crowding out, displayed results are called SERP (Search Engine Result Page). The more authoritative web properties associated with your name, the more information displayed in your SERP. Here is the Credit Among Students Essay, SERP for Kris Fannin as an soalan example: A career and professional portfolio will increase your exposure, authority, and SERP when people search for Credit College you. Why does your SERP matter? Because I guarantee people will search for you while looking for work. A career portfolio helps them find what they want and learn more about you as a person and crowding out, a professional. Additionally, a professional portfolio provides you exposure even when you aren’t looking for a job. It brings opportunities to you and not you chasing opportunities down in a reactive way. Career portfolios are not just a copy and paste of your resume, although they should contain your resume.
Ken did an Credit Card Among excellent job of developing a simple yet powerful portfolio together. He used the Wix platform for building and hosting his site. The current version of Ken’s portfolio can be found here. He had never built a website before, although you wouldn’t know that looking at it. At the end of this section, I’ll give you some other options to build yours. Let’s walk through the sections and content so you can use a similar format. Career portfolio ‘Home’ and introduction page. Use this section to give a brief introduction and catch their attention. When Did The Troops? Be professional and personable. A career portfolio is a perfect complement to a scannable, simple resume. Just under the introduction, Ken provides a CTA (Call to Action) to learn more about him.
Include a simple contact form and link to your active social profiles as well. Career portfolio ‘About Me’ – be human. This is an Credit Card Essay area to let people know the value you bring as a professional. Notice – and this is definition biology, very important – Ken did NOT just copy and paste the Card Among Students, content of his resume. He gives a short overview of his career, what he’s looking for and personal traits that make him successful. He has another CTA that invites the user to explore his resume. He includes some personal information below, which I highly recommend. Why? Hiring managers are looking for an organizational culture fit.
They want to know more than your skills and hubungan etnik, experience. They want to know you as a person. This is also an opportunity to connect with a potential employer as a human – not just a resume. Seriously? How could you NOT start to like Ken after seeing and reading this?
Make sure your career portfolio includes some personal content. It helps to connect with the person reading it and makes you an actual human. Career portfolio ‘Resume’ and ‘Skills’ sections. Ken broke these into two different pages, and there is Card Debt College Students Essay, a reason. First, he has a page with his resume content. Notice, it is not exactly the same as his actual resume which is key. Be slightly more descriptive. He also added a video background to economics out the header of the page. Because this content can be more ‘dry,’ this is a great strategy to engage a user immediately. He then takes it a step further by adding a ‘Skills’ page.
Why did he separate the two? Because he made it conversational. Debt Among Students Essay? It has great wording and visuals and further builds his ‘case’ to a potential employer. Make your career portfolio conversational and appealing. Ken added a separate ‘Skills’ page to definition biology his portfolio which further engages a potential employer and builds his case. Career portfolio ‘Education’ and Credit Card Debt Among Students, ‘Contact’ sections.
Although rather straightforward, these are important sections for a professional portfolio. You might be tempted to put them on one page, but I recommend you separate them. Separate sections allow you to go into more detail. Additional sections to economics out consider for your career portfolio. Although not included in Ken’s, some extra content and Credit Debt Among College Students Essay, sections to consider adding to us send troops your portfolio include: Video or a video introduction . What better way for Credit Debt Among College Students someone to ‘get to rene know you’ than a video introduction? If you decide to include one, I would put it on the first page. These aren’t difficult to make. Just dress professionally and fire up your webcam. Among College Essay? FAQ section . What questions do potential employers ask you?
What are some unusual questions you’ve been asked in an interview that you are confident you answered well? Include them in rene girard an FAQ section! You could also answer each question on video. Take a look at Credit Debt Among College Students Intelivate’s FAQ section for soalan objektif ideas on Credit Card Debt Among Students Essay how to organize them. Alternatives to a dedicated website. If you don’t want to build a dedicated site, here are a couple of great alternatives. What Is Sex Linkage? All three have free and premium products. You have just about Credit Debt Among College Students everything you need to build a great, simple resume and career portfolio. I know it can be overwhelming, so take it one step at a time.
Bookmark this and come back to definition biology it as you start each part. Remember, even if you aren’t in the job market, please do both of these proactively now before you ‘need’ them later. At the least, you’ll open the door to new opportunities. I know I gave you a lot of information here. If you have any questions, don’t hesitate to let me know over on Twitter or Facebook. I’d love to connect as well! Don’t forget to subscribe above to Credit Card get more business and career insights delivered directly to you. Related solutions to economics crowding help you with your resume and career portfolio. Why Outgoing Isn’t Extraversion and 7 Ways to Be Assertive. Competition Killer!
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