R—group: Its tendency is to interact with water at pH 7.

Example: Lys, Arg, and His

Unsubstitute (Example: Gly, Ala, Val, Leu, Ile, and Leu) Heterocyclic (Example: Pro) Aromatic (Example: Phe, Tyr, and Trp) Thioether (Example: Met) Hydroxy (Example: Ser and Thr) Mercapto (Example: Cys) Carboxamide (Example: Asn and Gln)

McGilvery and Goldstein-1979-grouped the 20 amino acids into monoamino– monocarboxylic acid, monoamino-dicarboxylic amino acid and diamino monocarboxylic acid.

Fairley and Kilgour, in 1966, grouped twenty amino acids into eight categories. Simple amino acids: No functional group in their side chain. Example: Gly, Ala, Val, Leu, and Ileu Hydroxy amino acids: Contain hydroxy group. Example: Ser and Thre Sulphur amino acids: Contain sulphur group. Example: Cys and Met Acidic amino acids: Contain carboxyl group. Example: Asp and Glu…

A comprehensive classification of amino acids is based on their structure and chemical nature. Each amino acid is assigned a three-letter or one-letter symbol. The twenty amino acids found in protein are divided into seven distinct groups. Example: Glycine. Glycine has the smallest functional group (hydrogen) of any of the α amino acids

There are different ways to classify the amino acids based on structure, chemical nature, nutritional requirement, metabolic fate, and so on.

Amino acids are termed as α-amino acids, if both the carboxyl and the amino groups are attached to the same carbon atom. The α-carbon atom binds to a side chain represented by R—, which is different for each amino acid found in proteins. Amino acids exist mostly in ionised form in the biological system.

Amino acids are a group of organic compounds containing two functional groups – amino and carboxyl. The amino group (NH 2) is the basic, while the carboxyl group (—COOH) is acidic in nature. Amino acids are the simplest unit of protein molecule, and they form the building blocks of protein structure.