Why are amino acids chiral?

1 Answer

All amino acids except glycine are chiral because they all contain at least one chiral centre.

The general formula for an amino acid is


The central carbon has four different groups attached. So the compound can exist as a pair of nonsuperimposable mirror images.


Thus, we can have D- and L-isomers of amino acids.

A rule of thumb for determining the D/L isomeric form of an amino acid is the "CORN" rule.

You arrange the groups CO OH, R, N, and H so that the H atom is pointing away from you.

If the arrangement of the CORN groups is counterclockwise, it is the L form.

All amino acids found in proteins have the L-configuration.

D-amino acids are not naturally found in proteins. They are not involved in the metabolic pathways of eukaryotic organisms.

D-amino acids are important in the structure and metabolism of bacteria. For example, D-alanine (below) is a structural component of certain bacterial cell walls.