l14_bioche_genet - MIT Department of Biology 7.014...

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7.014 Handout Biochemical Genetics MIT Department of Biology 7.014 Introductory Biology, Spring 2005
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Biochemical Genetics Introduction and Background We have learned that proteins can act as enzymes and catalyze all sorts of reactions in the cell. We discussed a biochemical approach to understanding cellular processes by purifying enzymes, determining their structure, and then studying the reactions they catalyze. Often though this type of study does not answer the question, "what does this protein do within the organism?" One approach to this question would be to remove the protein being studied and determine how this affects the organism. But, is this possible? The information required to make an enzyme is encoded as a gene in the DNA of the organism. In general, one gene corresponds to one polypeptide (a gene can also correspond to an RNA, but this is not relevant to the discussion at hand). This correspondence and advances in DNA technology allow researchers to create an organism that lacks a particular protein by removing the DNA that encodes that protein. In effect, a specific mutant organism can be created and by studying this mutant we can study the effects of removing a single protein. Even before this was a possibility, genetics played a key role in understanding many basic cellular processes. If you wanted to study olfaction but you had not identified any of the proteins involved, how could you begin? Because one gene corresponds to one protein and the genotype of an organism is often reflected in its phenotype, you could start by finding mutants that can not detect odors. The assumption would be that each mutant carries a change in the DNA that encodes a particular protein important in olfaction. The altered protein could have an altered function or be so changed that it no longer functions at all. The change in the DNA sequence is called a mutation, and the cell or organism carrying a mutation is called a mutant. Mutants with a disruption in the olfaction process would all have the same phenotype, an inability to sense odors. This is true even if each mutant had an alteration in a different gene. For example, assume that the ability to perceive odors requires three different proteins and protein 1 is encoded by gene1, protein 2 is encoded by gene 2, etc. The phenotype of an organism with a mutation in gene 1 would be the same as the phenotype of an organism with a mutation in a gene 2; neither of these mutants would be able to perceive an odor. Thus even without any knowledge of the genes or the proteins involved in a particular cellular process, we can begin to study it by collecting mutants that all display the same phenotype. A Model System For this introductory illustration of biochemical genetics we will begin with a model system. Model systems are organisms that can be easily manipulated in a laboratory environment.
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This note was uploaded on 05/02/2009 for the course BIOL 7.014 taught by Professor Walker during the Spring '05 term at MIT.

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l14_bioche_genet - MIT Department of Biology 7.014...

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