MCAT Biochemistry Question 2: Answer and Explanation
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Question: 2
2. At pH 7, the charge on a glutamic acid molecule is:
- A. –2.
- B. –1.
- C. 0
- D. 1
Correct Answer: B
Explanation:
Glutamic acid is an acidic amino acid because it has an extra carboxyl group. At neutral pH, both carboxyl groups are deprotonated and thus negatively charged. The amino group has a positive charge because it remains protonated at pH 7. Overall, therefore, glutamic acid has a net charge of –1, and choice (B) is correct. Notice that you do not even need to know the pI values to solve this question; as an acidic amino acid, glutamic acid must have a pI below 7.