Amino acid structure. Computer illustration showing the molecular structure of a typical amino acid. Amino acids are formed of an amine group (-NH2, circled, left) and carboxylic acid group (-COOH, circled, right) bonded to a side-chain (centre) that is specific to that amino acid. Amino acids have many roles in the human body. They bind together to form peptide chains, which in turn bind together into polypeptides. Proteins, the major component of muscles, are composed of one of more polypeptides arranged in a biologically functional way.