MCAT Biochemistry Question 9: Answer and Explanation
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Question: 9
9. A particular α-helix is known to cross the cell membrane. Which of these amino acids is most likely to be found in the transmembrane portion of the helix?
- A. Glutamate
- B. Lysine
- C. Phenylalanine
- D. Aspartate
Correct Answer: C
Explanation:
An amino acid likely to be found in a transmembrane portion of an α-helix will be exposed to a hydrophobic environment, so we need an amino acid with a hydrophobic side chain. The only choice that has a hydrophobic side chain is choice (C), phenylalanine. The other choices are all polar or charged.