Glutamine: An amino acid, one of the 20 building blocks of protein. Glutamine is present in plant and animal proteins. It can be synthesized by the body and is therefore not essential to the diet. Glutamine serves as an important carrier of ammonia and contributes it to the formation of urea and purines (which are essential to make DNA and RNA). Glutamine is broken down in the kidney. It was isolated in 1833 from beet juice but not synthesized until 1933. Symbol: Gln.