07exam3 - Micro 411/Genome Sci411 Exam Three 2-23-2007 Name...

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Micro 411/Genome Sci411 Exam Three 2-23-2007 Name _______________________________________ Question 1 . 20pts Diagram the initiation of recombination by RecBCD starting with double stranded DNA. Make sure to label all enzymes, the location of the Chi site and where RecA is required. A. 5’ 3’ 3’ 5’ B. Diagram RecBCD action at the site “B” in first diagram. C. Diagram RecBCD action at site “C”. D. Diagram D-loop formation with another double-stranded DNA molecule.
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Micro 411/Genome Sci411 Exam Three 2-23-2007 Question 2. 20pts. Four metabolites (A, B, C, D) are known to be involved in the biosynthesis of amino acid X. Structural analogs of each of these metabolites (A*, B*, C*, D*) are lethal to cells because they mimic the appropriate molecule and are used to form an aberrant form of X (= X*) that causes spontaneous termination of translation whenever it is incorporated into a polypeptide. Minimal glucose (MinGlu) medium containing each of these analogs individually was used to isolate conditional mutants that could grow in the presence of a given analog at 42°C, but not at 30°C. These mutants were then screened individually for growth at 42°C in the presence of each of the remaining three analogs. As shown in the table below, four mutant classes were identified by this analysis. (The “double mutant” is described in part D of this question.) Growth (+/-) at 42°C on MinGlu with: Mutant class A* B* C* D* No analog Number of isolates 1 - - + - + 600 2 + + - + + 200 3 - - - + + 200 4 + - - + + 200 Double mutant - - - - - n/a A) Assuming that all genetic loci involved are of equal mutational “target size”, how many
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07exam3 - Micro 411/Genome Sci411 Exam Three 2-23-2007 Name...

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