Problem Set 3

Problem Set 3 - Name_ TA/Section_ 7.012 Problem Set 3...

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Name_________________________________________ TA/Section_______________________ 7.012 Problem Set 3 Please print out this problem set and answer the questions on the print out. Answers to this problem set are to be turned in at the box outside 68-120 by 4:00, Friday, Oct. 12. Problem sets will not be accepted late. Solutions will be posted at: http://stellar.mit.edu/S/course/7/fa07/7.012/index.html Question 1 In a hypothetical type of yeast, the biosynthetic pathway for phenylalanine (shown below) has five reaction steps each catalyzed by a different enzyme (1 – 5). The enzymes are encoded by genes 1 – 5, respectively. The pathway is known to begin with phosphoenolpyruvate (PEP) and proceed via 4 intermediates W, X, Y, and Z to phenylalanine. PEP W X Y Z phenylalanine 1 2 3 4 5 You want to identify the five enzymes involved in this pathway by isolating yeast that fail to synthesize phenylalanine (these yeast are referred to as “phe - ”). You know that mutant yeast that fail to synthesize phenylalanine (and thus can not grow without addition of phenylalanine) are likely to be defective in one of the enzymes involved in the phenylalanine synthesis pathway. You start with a population of wild-type (“phe + ”) yeast, mutagenize it with UV light, and allow the treated cells to grow into isolated colonies on plate 1 (see FIGURE 1). You then use the replica plating technique to transfer some yeast from each colony onto plates 2, 3, 4, and 5. The contents of the growth medium are listed below each plate. Rich medium contains all nutrients and allows growth of both wild type, and mutant cells. Minimal medium contains nutrients sufficient to allow only wild-type, protoptrophic yeast to grow. It will not support the growth of auxotrophic cells. FIGURE 1:
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This note was uploaded on 11/10/2009 for the course 7 7.012 taught by Professor Lander during the Fall '08 term at MIT.

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Problem Set 3 - Name_ TA/Section_ 7.012 Problem Set 3...

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