MCAT Biochemistry Question 16: Answer and Explanation

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Question: 16

1. Consider a biochemical reaction A → B, which is catalyzed by A–B dehydrogenase. Which of the following statements is true?

  • A. The reaction will proceed until the enzyme concentration decreases.
  • B. The reaction will be most favorable at 0°C.
  • C. A component of the enzyme is transferred from A to B.
  • D. The free energy change (ΔG) of the catalyzed reaction is the same as for the uncatalyzed reaction.

Correct Answer: D

Explanation:

Enzymes catalyze reactions by lowering their activation energy, and are not changed or consumed during the course of the reaction. While the activation energy is lowered, the free energy of the reaction, ΔG, remains unchanged in the presence of an enzyme. A reaction will continue to occur in the presence or absence of an enzyme; it simply runs slower without the enzyme, eliminating choice (A). Most physiological reactions are optimized at body temperature, 37°C, eliminating choice (B). Finally, dehydrogenases catalyze oxidation–reduction reactions, not transfer reactions, eliminating choice (C).

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