Proteinogenic

Proline is the only proteinogenic amino acid whose side-group links to the α-amino group and, thus, is also the only proteinogenic amino acid containing a secondary amine at this position.

Nine proteinogenic amino acids are called "essential" for humans because they cannot be created from other compounds by the human body and so must be taken in as food.

Proteinogenic amino acids seeAlso The amino acid selenocysteine Amino acids are the structural units (monomers) that make up proteins.