MCAT Biochemistry Question 1: Answer and Explanation

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Question: 1

1. In a neutral solution, most amino acids exist as:

  • A. positively charged compounds.
  • B. zwitterions.
  • C. negatively charged compounds.
  • D. hydrophobic molecules.

Correct Answer: B

Explanation:

Most amino acids (except the acidic and basic amino acids) have two sites for protonation: the carboxylic acid and the amine group. At neutral pH, the carboxylic acid will be deprotonated (–COO–), and the amine group will remain protonated (–NH3+). This dipolar ion is a zwitterion, so choice(B) is the correct answer.

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