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Scott_QUIZ2-KEY - MCB 104 Quiz#2 25 points possible Name...

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MCB 104 Quiz #2 Name: 3/17/2010 25 points possible SID: Note: I have included explanations to help you study. Explanations were not required to receive full credit on this quiz. All that was required was the pathway, compound, phenotype, or ratio, as required by the question prompt. 1. Unbeknownst to many, Guinness beer is actually the byproduct of a biosynthetic pathway through which a special yeast strain converts potatoes into an essential nutrient. Each step in the pathway is catalyzed by one enzyme. Brewmaster Seamus O’Reilly notices that each of his yeast strains has acquired a single loss-of-function mutation in a biosynthetic enzyme, and is no longer viable, and therefore cannot make the nutrient or the Guinness. The four mutant strains (and corresponding enzymes) are Aidan, Bailey, Colin, and Duffy. Seamus discovers that by adding nutrients from his Lucky Charms cereal back to the culture, he is able to restore the viability, and therefore the Guinness- making ability of the yeast: (- = lethal; + = viable) 1A [3 points]. What is the order of the pathway? In each blank space, list the intermediate compound. Above each arrow, write the enzyme that catalyzes the step. C B A D _ potatoes_ _ balloons _ _ stars___ _ horseshoes _ hearts _ D must be the most downstream enzyme b/c it is rescued by the fewest intermediates. C must be the most upstream enzyme b/c it is rescued by the most interemediates. Pink hearts must be the most downstream intermediate b/c they rescue all of the mutants.
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