3718108165 - Chemistry 3785 Third Hour Exam 100 points...

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1 Chemistry 3785 Third Hour Exam Name KEY 100 points Points Score Points Score I 48 IV 12 II 14 V 14 III 12 Total 100 I. (48) Multiple Choice. Circle the letter corresponding to the best choice. Three points each. 1. Which of the following statements about a plot of v 0 vs [S] for an enzyme that follows Michaelis-Menten kinetics is false ? a. As [S] increases, the initial velocity of the reaction also increases. b. At low [S] the rate of reaction is directly proportional to the substrate concentration. c. K M is the [S] at which v o = ½V max . d. The curve assumes the shape of a hyperbola. e. At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at K M . 2. Michaelis and Menten assumed that the overall rate for an enzyme-catalyzed reaction could be written as Using this reaction, the rate of ES complex formation can be described by the expression: a. k 1 [E][S]. b. k 1 ([E] T - [ES])[S]. c. k 1 [E][S] + k 2 [E][P] . d. k- 1 [ES] + k 2 [ES]. e. k- 1 [ES] 3. Find the initial velocity for a reaction where V max = 6.5 × 10 -5 mol sec -1 , [S] = 3.0 × 10 -3 M, and K M = 4.5 × 10 -3 M. a. 1.4 × 10 -2 mol sec -1 b. 2.6 × 10 -5 mol sec -1 c. 8.7 × 10 -3 mol sec -1 d. 3.9 × 10 -5 mol sec -1 e. 4.3 × 10 -5 mol sec -1 4. The best measure of catalytic efficiency under physiological conditions is a. k cat b. V max c. V max /K M d. k cat /K M e. k -1 /k 1 E + S ES E + P k 1 k -1 k 2
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2 5. For an enzyme that follows Michaelis-Menten kinetics, K M can be considered the same as the dissociation constant of the ES complex, K S , when a. ES E + P is fast compared to ES E + S. b. k cat is very large. c. k 2 << k -1 d. k cat /K M is near the diffusion controlled limit. e. none of the above. 6. Which statement is true concerning the structure and function of aspartate transcarbamoylase (ATCase)? a. ATCase is allosterically activated by glutamine. b. CTP is a feedback inhibitor of the enzyme. c. The catalytic subunits are related by a three-fold rotation axis. d. The regulatory subunits bind carbamoyl phosphate and aspartate. e. both b and c are true. 7. What is true concerning the regulation of ATCase by ATP? a. Two sites exist on ATCase for ATP binding. One is a substrate site and one is an inhibitor site. b. ATP is an allosteric activator, increasing the enzyme’s affinity for its substrate. c. The sigmoidal curve for rate vs. substrate shifts to the right. d. The K M for aspartate increases in the presence of ATP. e.
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This note was uploaded on 11/24/2011 for the course BIO 400 taught by Professor Raganbower during the Winter '10 term at Drexel.

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3718108165 - Chemistry 3785 Third Hour Exam 100 points...

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