Exam 3 2008 - NAME _ 1) Within a factor of 2, what are the...

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NAME __________________________ 1) Within a factor of 2, what are the sizes of the E. coli, Saccharomyces cerevisiae (yeast)(haploid), and human (haploid) genomes? Give the answer in number of base pairs and number of genes. (6pts) 2) In class we discussed many ways in which the amount of proteins in the cell can be controlled by the cell. Please list three steps at which protein synthesis is controlled and include which of these is the most important control point. (4pts) 3) The cell also contains a system to control the amount of proteins after they have been synthesized (i.e., translated). Describe the basic principles of this control system naming the three components (one protein machine or very large complex with enzymatic activity; a cascade of enzymes, and a tag). (4pts) 4) Bacterial cells can take up from the environment many nutrients and amino acids, including the 1
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NAME __________________________ amino acid tryptophan (Trp). However, if the supply of amino acids is low, many bacteria can also synthesize them from other small molecules. The Trp repressor is a gene regulatory protein that shuts off the transcription of genes that code for the enzymes required for Trp synthesis. Trp repressor binds the operator region of the Trp operon only when Trp is present. A. What would happen to the regulation of the Trp biosynthesis enzymes in cells that express a mutant form of Trp repressor that has a point mutation in the second alpha helix of its DNA binding motif so that it can no longer bind DNA? (2pts) B. What would happen in the situations described in part A if the cells in addition would also express wildtype (normal) Trp repressor from a second gene at the same level as the mutant Trp repressor? (2 pts) C. What would happen in the situations described in part B if the cells in addition would also express wildtype (normal) Trp repressor from a second gene at much higher levels than the mutant Trp repressor? (2 pts) D. What would happen to the regulation of the Trp biosynthesis enzymes in cells that express a mutant form of Trp repressor that always binds DNA independent of the presence or absence of Trp in the surroundings (2 pts)? 2
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NAME __________________________ E. Your friend, a freshman at Northwestern, has just started doing independent research in the a bacterial genetics lab where she makes the following observations working with a new mutant strain of E. coli: The mutant bacteria always express the Trp biosynthesis enzymes even in the absence of Trp in the culture medium and when she expresses normal Trp repressor in large amounts from a plasmid. Otherwise the bacteria are healthy and grow well. Being nice, you’re solving the problem for her: Where is the mutation or what does it do? (2pts) 5) We have discussed how the lac operon (see figure below) is controlled by both the CAP activator protein and the lac repressor. You create cells that are mutant in the gene coding for the
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Exam 3 2008 - NAME _ 1) Within a factor of 2, what are the...

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