Classification of α-Amino Acids

Amino acids are classified primarily on the nature of their R group, commonly called the side chain. Based on the chemical character of this side chain, amino acids are grouped as acidic, basic or neutral; they can also be grouped along a second, independent axis as polar or non-polar (hydrophobic), depending on whether the side chain can hydrogen-bond with water.

A third, biologically important classification splits the twenty amino acids into essential and non-essential amino acids, based on whether the human body is able to synthesise them itself. The amino acids the body CAN synthesise are the non-essential amino acids: glycine (Gly), alanine (Ala), glutamic acid (Glu), aspartic acid (Asp), glutamine (Gln), asparagine (Asn), serine (Ser), cysteine (Cys), tyrosine (Tyr) and proline (Pro) -- ten in all. The remaining ten, which the body cannot synthesise and which must therefore be obtained through the diet, are the essential amino acids: phenylalanine (Phe), valine (Val), threonine (Thr), tryptophan (Trp), isoleucine (Ile), methionine (Met), histidine (His), arginine (Arg), leucine (Leu) and lysine (Lys). These ten essential amino acids are commonly memorised using the mnemonic 'PVT TIM HALL' (Phe-Val-Thr, Trp-Ile-Met, His-Arg-Leu-Lys). …