The R group is what makes amino acids different. It’s also called a side chain. The R group gives each amino acid its unique properties. It’s what separates each of the 20 amino acids.

Each of the 20 amino acids has a specific side chain, known as an R group, that is also attached to the α carbon. The R groups have a variety of shapes, sizes, charges, and reactivities.

Amino acids are characterized by their central carbon atom, known as the α-carbon, which is bonded to an amino group (-NH2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain ...