Glutamine
Glutamine (symbol Gln or Q) is an α-amino acid that is used in the biosynthesis of proteins. Its side chain is similar to that of glutamic acid, except the carboxylic acid group is replaced by an amide. It is classified as a charge-neutral, polar amino acid. It is non-essential and conditionally essential in humans, meaning the body can usually synthesize sufficient amounts of it, but in some instances of stress, the body's demand for glutamine increases, and glutamine must be obtained from the diet. It is encoded by the codons CAA and CAG.
Non-proteinogenic amino acids
In biochemistry, non-coded or non-proteinogenic amino acids are those not naturally encoded or found in the genetic code of any organism.
Despite the use of only 22 amino acids (21 in eukaryotes) by the translational machinery to assemble proteins (the proteinogenic amino acids), over 140 amino acids are known to occur naturally in proteins and thousands more may occur in nature or be synthesized in the laboratory.
Many non-proteinogenic amino acids are noteworthy because they are;