Glycine (symbol Gly or G ;  / ˈ ɡ l aɪ s iː n / )  is an amino acid that has a single hydrogen atom as its side chain . It is the simplest amino acid, with the chemical formula NH 2 ‐ CH 2 ‐ COOH . Glycine is one of the proteinogenic amino acids . It is encoded by all the codons starting with GG (GGU, GGC, GGA, GGG). Glycine is also known as a "helix breaker", due to its ability to act as a hinge in the secondary structure of proteins.