MCAT Biochemistry Question 168: Answer and Explanation

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Question: 168

3. Which of the following statements is true about the hydrolysis of ATP?

  • A. The free energy of ATP hydrolysis is independent of pH.
  • B. One mole of creatine phosphate can phosphorylate two moles of ADP.
  • C. The free energy of hydrolysis of ATP is nearly the same as for ADP.
  • D. ATP yields cyclic AMP after two hydrolysis reactions.

Correct Answer: C

Explanation:

The hydrolysis of ATP is energetically favorable because there are repulsive negative charges that are relieved when hydrolyzed, and the new compounds are stabilized by resonance. This is true of both ATP and ADP. Some of the other answer choices are tempting, though. In choice (A), ATP hydrolysis relies on pH because a protonated ATP molecule experiences less repulsive force. For choice (B), the energy released by one mole of creatine phosphate upon hydrolysis is not sufficient to phosphorylate two moles of ADP according to Table 12.1. For choice (D), the removal of two phosphate groups from ATP yields AMP, not cyclic AMP.

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