What Is Amino Acid?

Amino acids are organic molecules containing an amino group (-NH2), a carboxyl group (-COOH), and a variable side chain (R group) that determines each amino acid's unique chemical properties. The 20 standard amino acids encoded by DNA include nonpolar residues like glycine and alanine, polar residues like serine and threonine, and charged residues like lysine and glutamate. Peptide sequences are written from the N-terminus (amino end) to the C-terminus (carboxyl end). The specific sequence of amino acids determines a peptide's three-dimensional structure, receptor binding properties, and biological activity. Synthetic peptide research also uses non-standard amino acids and chemical modifications to improve stability or alter activity.