Amino acids are organic compounds that serve as the fundamental building blocks of proteins in living organisms. They contain a central carbon atom (alpha carbon) bonded to a hydrogen atom, a carboxyl group (-COOH), an amino group (-NH₂), and a variable side chain (R group) that determines the unique properties of each amino acid. In biological systems, amino acids link together via peptide bonds to form polypeptides and proteins, which perform essential functions like enzyme catalysis, structural support, immune response, and hormone regulation.