An amino acid contains an amino group, a carboxyl group and a hydrogen atom. All these groups are bounded to a central carbon known as the a-carbon atom. The fourth position is the only variable part of the molecule. The group here is known as the R group. This group gives each amino acid its uniqueness. The chemical nature and identity of each amino acid is determined by the radical R, which actually varies from one amino acid to other, with either hydrogen or aliphatic, aromatic or heterocyclic group attached.
