The reason why amino acids are different is determined by the R group. Amino acids are the basic building blocks of proteins, which are organic compounds containing a basic amino group and an acidic carboxyl group, and the R group is the fourth group attached to the carbon atom of an amino acid. Amino acid molecules contain both amino and carboxyl functional groups. They are classified into different amino acids according to the R substituent group.20 Protein amino acids differ structurally depending on the side-chain genes R. The amino acids are usually classified into different groups according to their chemical structure. The 20 amino acids are usually categorized according to the chemical structure and properties of the R group. 1. Aromatic amino acids: phenylalanine, tyrosine. 2. Heterocyclic amino acids: histidine, tryptophan. 3. Aliphatic amino acids: C, Val, Leucine, Isoleucine, Egg, Aspartic, Grain, Lysine, Arginine, Glycine, Silk, Sulphur, Cysteine, Asparagine, Glutamine. 4. Heterocyclic subamino acids: proline. The reason for the diversity of protein molecular structure is the difference in the type, number, order and spatial structure of amino acids.