PSET3Q - Name_ 2010 7.012 Problem Set 3 Section_ TA_ Please...

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Name_____________________________________ Section_______ TA_____________ 1 2010 7.012 Problem Set 3 Please print out this problem set and answer the questions on the printout. Answers to this problem set are to be turned in at the box outside 68-120 before 1:15 pm, Friday Oct 1 st . Question 1 The following schematic represents the only pathway for the synthesis of the amino acid lysine in yeast cells. Each step in this pathway is catalyzed by a specific enzyme, which is encoded by a specific gene. This pathway begins with a hypothetical compound A and proceeds via three intermediates B, C and D to produce lysine. A yeast cell that is missing any of genes encoding these four enzymes cannot synthesize lysine. A cell that cannot synthesize lysine cannot grow and form a colony on minimal media (media that does not have any added supplements) but can grow and form a colony on media that contains lysine. You do a mutant hunt to identify the enzymes that are involved in lysine biosynthesis. You start with a population of wild type yeast cells, mutagenize them using UV and allow the UV irradiated cells to grow and divide on a master plate containing rich medium (i.e. medium containing all essential compounds and added supplements). You then replica plate the cells from each colony on the master plate to the following plates containing minimal media or minimal media and the specified nutrients. a) From these plates… i) Identify the colony or colonies of wild-type cells. Explain why you selected these colonies. ii) Assume that each colony is composed of cells that carry a single mutation. Identify the colony or colonies of cells that cannot synthesize lysine. Explain why you selected these colonies. iii) Identify the colony or colonies of cells that carry a mutation in a gene that codes for a protein involved in biosynthetic pathway different from the lysine biosynthetic pathway. Explain why you selected this colony or colonies. iv) Identify the colony or colonies of cells that carry a mutation in either the gene that encodes the enzyme that converts A B or the gene that encodes the enzyme that converts B C. Explain
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PSET3Q - Name_ 2010 7.012 Problem Set 3 Section_ TA_ Please...

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