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WWU CHEM 473 - Second Exam

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Chem/Biol 473 Second Exam May 16, 2007 Name_______________1. (15 points) Dr. McCoy is analyzing the metabolism of sugars by a (very rare) enteric bacterium from the planet Sargon VII. This bacterium preferentially utilizes the (equally rare) sugar pretendolose but can also metabolize the (slightly more abundant) sugar scarcelose. Whenever pretendolose is present in the medium, the pretendolose operon is transcribed, and the scarcelose operon not, regardless of the presence of scarcelose. Whenever pretendolose is absent from the medium, the scarcelose operon is expressed,and the pretendolose genes are not, regardless of the presence of scarcelose. Experiment Sugars inmediumTranscription ofpretendolose (P) operonTranscription ofscarcelose (S) operon1 P + -2 P+S + -3 S - +4 - - +A. Propose one mechanism of regulation for these two operons that would explain this data.Why do you think such control evolved?2. (5 points) Many prokaryotic and eukaryotic translation factors have a domain in common which is not involved in binding to RNA or the ribosome. What might the function of this domain be?3. (20 points)Based on this data, answer the following questions:a. How long is the family of sites recognized by this protein? What is the consensus sequence?b. In the first draft of the paper discussing this experiment, your student writes that “based on the recovery data, the protein appears to make contacts with a run of six base pairs in its DNA target”. Is this conclusion correct based on the data shown? Why or why not?c. What would you predict about the structure of this DNA-binding protein basedon the selection data shown above?d. Comment on the possible determinants of the specificity of the protein bindingto its target.4. (8 points) Why would ribosomal backtracking not work as a proofreading systemfor protein synthesis in the same manner that backtracking works for transcription?5. (12 points) Charles Yanofsky and his associates have synthesized a 15 nucleotide RNA that is complementary to segment 1 of the trp leader. What isits effect on the in vitro transcription of the trp operon? Explain.What is the effect if the leader contains a mutation in segment 2 that destabilizes the 2-3


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