What is the definition of an amino acid?

Amino acids are organic compounds that serve as the building blocks of proteins. Each amino acid contains a basic amino group (-NH2), an acidic carboxyl group (-COOH), and a unique side chain or R group that determines the characteristics of each individual amino acid. When amino acids link together through peptide bonds, they form proteins, which play crucial roles in the structure and function of cells.

The correct choice highlights the foundational role that amino acids play in protein synthesis, making it essential for numerous biological processes, including enzyme function, cell signaling, and immune responses. This definition accurately reflects the significance of amino acids in biochemistry and their contribution to the overall functioning of living organisms.