alpha- Amino acids are the building blocks of proteins. About 20 alpha-amino acids have been isolated by the hydrolysis of proteins. All these amino acids except glycine are chiral and have L-configuration. Ten amino acids (valine , leucine, isoleucine , phenylalanine, methionine , trytophan , threonine , lysine , arginine and histidine) which the body cannot synthesize are called essential amino acids. The remaining ten are called non -essential amino acids. All alpha-amino acids exist are zwitterions each of which has a specific isoelectric point. Above isoelectric point , a alpha-amino acid exists as an anion. Two, three or many alpha-amino acids join together to form di-,tri -or polypeptides or proteins respectively. Each polypeptides or protein has a free amino group at one end called the N-terminal end and a free carboxyl group at the other end called the C-terimal end. Sanger's reagent (i.e., 2,4-dinitrofluorobenzene) is used to determine the N-terminal end while C-terimal end is determined by hydrazinolysis. An alpha-amino below its isoelectric point exists as