The correct answer is the R group, or side chain. Each amino acid has a specific chemical structure that includes a central carbon atom bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and an R group. The R group varies among different amino acids and is what determines the unique properties and functions of each amino acid. The peptide group is a chemical bond that connects amino acids together to form proteins, while the amino and carboxyl groups are functional groups present in all amino acids.
