MCAT Biochemistry Question 13: Answer and Explanation
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Question: 13
13. In lysine, the pKa of the side chain is about 10.5. Assuming that the pKa of the carboxyl and amino groups are 2 and 9, respectively, the pI of lysine is closest to:
- A. 5.5.
- B. 6.2.
- C. 7.4.
- D. 9.8.
Correct Answer: D
Explanation:
Because lysine has a basic side chain, we ignore the pKa of the carboxyl group, and average the pKa of the side chain and the amino group; the average of 9 and 10.5 is 9.75, which is closest to choice (D).