Glutamine

(CC) Image: David E. Volk
Glutamine, a common amino acid.

Glutamine, abbreviated Gln or Q, is one of the twenty common $\alpha$-amino acids used by living organisms to build proteins. It is closely related to the acidic amino acid glutamic acid which has a carboxylic acid in place of the amide group present in glutamine. Glutamine is a neutral but polar amino acid. Asparagine has a similar structure with a side chain that is one carbon atom shorter.