Computer graphics space-filling representation of the amino acid alanine, displayed in its L- and D- forms (left- and right-handed forms). Amino acids are building- blocks of larger protein molecules. The 20 common amino acids all possess a similar core structure of a carboxyl (COOH) group at one end and an amino (HNH) group at the other, but each is distinguished by having a different side- chain structure. Varying numbers of different amino acids combine to form the variety of proteins. Other smaller molecules (peptides and oligopeptides) are made from amino acids - the hormone insulin, for example. This image was modelled using Chemical Design's Chem-X software.