XM05key - MCB 100B Fall 2005 M D Alper MIDTERM...

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M. D. Alper Fall 2005 October 12, 2005 MIDTERM EXAMINATION-KEY 1. (25 pts). Citrate -- CH 2 COOH | HOCCOOH | CH 2 COOH is an intermediate in the metabolism of glucose. It is converted to isocitrate. a. Citrate is an intermediate in which pathway? Krebs cycle, tricarboxylic acid cycle, citric acid cycle b. Which product of earlier steps in glucose metabolism enters this pathway for further metabolism. Acetyl CoA c. Name the five primary products of this pathway. GTP, CO 2 , NADH, FADH 2 , CoASH d. Circle the carbon atom on citrate (above) that becomes the OH carrying carbon of isocitrate. Explain your answer fully. The methylene carbon atom that was not delivered by Acetyl CoA in the production of that molecule of citrate. Eventually, in later rounds of the cycle, the carbon delivered by acetyl CoA will receive the OH. e. Which reaction in the fermentation of glucose illustrates the principle that you invoked in your answer to Question 1d. Explain. The conversion of acetaldehyde and ethanol. The two hydrogens on the hydroxyl carbon of ethanol are equivalent, as are the two methylene carbons in citrate but, as Westheimer showed in his experiments with deuterated ethanol, the enzyme distinguishes between the two because it presents a surface on which three groups of the substrate bind, thus presenting only one of the methylene carbons of citrate or one of the hydrogens of ethanol for reaction. 2. (10 pts) The redox potential of FAD + 2H FADH 2 is -0.22V. The redox potential of NAD + 2H NADH + H + is -0.32 volts. If FAD were used in the glycolytic reaction in which glyceraldehyde phosphate is oxidized, would the standard free energy of that
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XM05key - MCB 100B Fall 2005 M D Alper MIDTERM...

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