In amino acids, what structural feature primarily gives each amino acid its unique chemical properties?

• A. The side chain (R group) attached to the $C$${\alpha }_{}$-carbon
• B. The peptide bond between amino acids
• C. The amino group (${\mathrm{NH}}_2$)
• D. The carboxyl group (${\mathrm{COOH}}_{}$)

Answer: (A)

Verified step by step guidance

1. Understand the general structure of an amino acid, which includes a central alpha-carbon (C\_\(\alpha\)) bonded to four groups: an amino group (NH\_2), a carboxyl group (COOH), a hydrogen atom, and a variable side chain (R group).
2. Recognize that the amino group and carboxyl group are common to all amino acids and are involved in forming peptide bonds during protein synthesis, so they do not confer uniqueness to each amino acid.
3. Focus on the side chain (R group) attached to the alpha-carbon, which varies in size, charge, polarity, and chemical reactivity among different amino acids.
4. Realize that these differences in the side chain are what give each amino acid its unique chemical properties, such as hydrophobicity, acidity, basicity, and ability to form specific interactions.
5. Conclude that the primary structural feature responsible for the unique chemical properties of each amino acid is the side chain (R group) attached to the alpha-carbon.