All α-amino acids except glycine CH<sub>2</sub>(NH<sub>2</sub>)COOH and proline are complex enough to have the two [[optical isomerism|optical isomers]] that are mirror images of each other (L and R). This is because they have four different groups around the alpha carbon, forming a [[chiral centre]]. | All α-amino acids except glycine CH<sub>2</sub>(NH<sub>2</sub>)COOH and proline are complex enough to have the two [[optical isomerism|optical isomers]] that are mirror images of each other (L and R). This is because they have four different groups around the alpha carbon, forming a [[chiral centre]]. |