Ch. 13 Lehninger biochem test bank Exam 2023 -2024 1. If the delta G'° of the reaction A --> B is -40 kJ/mol, under standard conditions the reaction: A) is at equilibrium. B) will never reach equilibrium. C) will not occur spontaneously. D) will proceed at a rapid rate. E) will proceed spontaneously from A to B. - Answer E For the reaction A --->B, delta G'° = -60 kJ/mol. The reaction is started with 10 mmol of A; no B is initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A. Which is the most likely explanation? A) A and B have reached equilibrium concentrations. B) An enzyme has shifted the equilibrium toward A. C) B formation is kinetically slow; equilibrium has not been reached by 24 hours. D) Formation of B is thermodynamically unfavorable. E) The result described is impossible, given the fact thatG'° is -60 kJ/mol. - Answer C The reaction A + B --->C has a delta G'° of -20 kJ/mol at 25° C. Starting under standard conditions, one can predict that: A) at equilibrium, the concentration of B will exceed the concentration of A. B) at equilibrium, the concentration of C will be less than the concentration of A. C) at equilibrium, the concentration of C will be much greater than the concentration of A or B. D) C will rapidly break down to A + B. E) when A and B are mixed, the reaction will proceed rapidly toward formation of C. - Answer C Which of the following compounds has the largest negative value for the standard free-
energy change (G'°) upon hydrolysis? A) Acetic anhydride B) Glucose 6-phosphate C) Glutamine D) Glycerol 3-phosphate E) Lactose - Answer A For the following reaction, delta G'° = +29.7 kJ/mol. L-Malate + NAD+ --->oxaloacetate + NADH + H+ The reaction as written: A) can never occur in a cell. B) can occur in a cell only if it is coupled to another reaction for which delta G'° is positive. C) can occur only in a cell in which NADH is converted to NAD+ by electron transport. D) cannot occur because of its large activation energy. E) may occur in cells at some concentrations of substrate and product. - Answer E For the reaction A --->B, the Keq' is 104. If a reaction mixture originally contains 1 mmol of A and no B, which one of the following must be true? A) At equilibrium, there will be far more B than A. B) The rate of the reaction is very slow. C) The reaction requires coupling to an exergonic reaction in order to proceed. D) The reaction will proceed toward B at a very high rate. E) Delta G'° for the reaction will be large and positive. - Answer A For the reaction A --->B, the Keq' is 10-6. If a reaction mixture originally contains 1 mmol of A and 1 mmol of B, which one of the following must be true? A) At equilibrium, there will be still be equal levels of A and B. B) The rate of the reaction is very slow. C) At equilibrium, the amount of A will greatly exceed the amount of B . D) The reaction will proceed toward B at a very high rate. E) Delta G'° for the reaction will be large and positive. - Answer A In glycolysis, fructose 1,6-bisphosphate is converted to two products with a standard free-energy change (delta G'°) of 23.8 kJ/mol. Under what conditions encountered in a normal cell will the free-energy change (delta G) be negative, enabling the reaction to proceed spontaneously to the right? A) Under standard conditions, enough energy is released to drive the reaction to the right. B) The reaction will not go to the right spontaneously under any conditions because theG'° is positive. C) The reaction will proceed spontaneously to the right if there is a high concentration o f products relative to the concentration of fructose 1,6-bisphosphate. D) The reaction will proceed spontaneously to the right if there is a high concentration o f fructose 1,6-bisphosphate relative to the concentration of products.
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