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classes_spring08_153A-1ID29_080529_MidtermII_KEY

classes_spring08_153A-1ID29_080529_MidtermII_KEY - LAST...

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LAST NAME___________________ - 2 - 1. Which one of the following statements is true with respect to enzyme cofactors? (2 pts) a) A holoenzyme is the protein part of an enzyme that is not catalytically active until a cofactor is bound. b) Inorganic metal ions are examples of coenzymes. c) Cofactors that are tightly or covalently bound to an enzyme protein are called prosthetic groups. d) Enzyme cofactors are proteins. 2 . Circle the one statement that is true with respect to an enzyme ternary complex that follows a ping-pong pathway. (2 pts) a) The order of substrate binding is random. b) Upon binding the first substrate the enzyme can next bind the second substrate simultaneously. c) The family of lines plotted on a double reciprocal plot (1/V 0 versus 1/S 1 ) all intersect to the left of the y-axis as [S 2 ] increases. d) The family of lines plotted on a double reciprocal plot (1/V 0 versus 1/S 1 ) all share the same slope when [S 2 ] increases. 3 . Circle the best answer that completes the sentence. In a monosubstrate enzyme catalyzed reaction, a simple plot of V 0 versus [S] is superior to a double-reciprocal plot (1/V 0 versus 1/[S]) if you are trying to _________. (2 pts) a) determine V max . b) detect allosteric regulation. c) determine the type of inhibition. d) determine the K m . 4 . Circle the one answer that best completes the sentence. An enzyme with a high turnover number has ______________. (2 pts) a) a high K cat . b) a low K m . c) a high V max . d) a high K ca t/K m . 5 . In what way does the binding of a substrate in the active site of an enzyme enhance catalysis? Circle the one best answer. (2 pts) a) It increases the interaction of the substrate with water. b) The binding energy of the enzyme-substrate interaction lowers the activation energy. c) It increases the entropy between substrates. d) The binding of a substrate prevents the enzyme from changing conformation. 6 . Circle the best answer. In competitive inhibition, increasing concentrations of the inhibitor will have what effect on the kinetics of the enzyme? (2 pts) a) Apparent K m will decrease. b) Apparent V max will stay the same. c) The reaction will cease because the inhibitor binds the active site irreversibly. d) The ratio of apparent K m to apparent V max will stay the same. 7 . In the box, define the Michaelis constant in terms of rate constants. (2 pts) 8 . Theoretically the reaction rate of an enzyme increases with temperature. In practice, however, this is generally not the best way to increase the rate. Why? Be very specific. (2 pts) Temperature will disrupt the weak interactions that maintain the 3D structure of the enzyme. So as temperature increases an enzyme will lose its native conformation (denature), which will inhibit/abolish its activity. Km = (k -1 + k 2 )/k 1
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- 3 - 9 . Circle the best answer that completes the sentence. The initial velocity of a reaction was measured in the presence of varying concentrations of substrate and inhibitor.
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