Answer:
A
Explanation:
Let's analyze the options:
A. Methionine - Methionine has a nonpolar side chain (-CH2-S-CH3), making it a nonpolar amino acid. [Source: Biochemistry: Methionine]
B. Serine - Serine has a polar side chain (-CH2OH), making it a polar amino acid. [Source: Biochemistry: Serine]
C. Tyrosine - Tyrosine has a polar side chain (-CH2-Ph-OH), making it a polar amino acid. [Source: Biochemistry: Tyrosine]
D. Histidine - Histidine has a polar side chain (-CH2-NH-CH=N-CH2), making it a polar amino acid. [Source: Biochemistry: Histidine]
Therefore, the amino acid with a nonpolar side chain among the given options is A. Methionine.