Which set correctly lists the four groups bonded to the central (alpha) carbon in the standard amino acid structural template?

• A. Hydrogen atom, amine group, methyl backbone, and R group which is identical across all 20 amino acids and therefore does not affect their properties
• B. Hydroxyl group, sulfur-containing thiol group, phosphate group, and variable R side chain that determines hydrophobicity and size
• C. Hydrogen atom, phosphate group, carboxyl group, and R group containing a nitrogen atom in every amino acid
• D. Hydrogen atom, amine group (—NH2), carboxyl group (—COOH), and variable R (side chain)

Answer: (D)