Amino Acid Chirality

Amino acids (except for glycine) have a chiral carbon atom adjacent to the carboxyl group (CO₂^-). This chiral center allows for stereoisomerism. For example, take a look at the stereorepresentations and Fischer projection formulas of the enantiomers of serine.

All amino acids found in proteins occur in the L-configuration about the chiral carbon atom. D-amino acids are not naturally found in proteins and are not involved in the metabolic pathways of eukaryotic organisms, although they are important in the structure and metabolism of bacteria. For example, D-glutamic acid and D-alanine are structural components of certain bacterial cell walls.