MCAT Biochemistry Question 12: Answer and Explanation

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Question: 12

12. Which of these amino acids has a side chain that can become ionized in cells?

  • A. Histidine
  • B. Leucine
  • C. Proline
  • D. Threonine

Correct Answer: A

Explanation:

Histidine has an ionizable side chain: its imidazole ring has a nitrogen atom that can be protonated. None of the remaining answers have ionizable atoms in their side chains.

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