Ans. is 'b' i.e., Amino acids Impoant chemical reactions of amino acids Following are some impoant chemical reactions. A. Reaction used to determine amino acid sequence in polypeptide chain : - Generally, amino terminal (N-terminal) of amino acid is tagged with some reagent. It is split off by hydrolysis and tagged amino acid is identified. The reaction is, then, repeated with new N-terminal of subsequent amino acid and so on. The two reactions are used for identification of amino acid sequence : ? Sanger's reaction : - Uses Sanger's reagent ( 1 -fluoro-2,4-dinitrobenzene) to tag amino terminal. Edman's reaction : - Uses Edman's reagent (phenylisothiocyanate) to tag amino terminal. B. Reaction used to identification of individual or group of amino acids : - These reactions are frequently used for qualitative detection and quantitative measurement of various amino acids. Ninhydrin tese : - All a-amino acids. Xanthophoretic reaction : - Aromatic amino acidse (Tyrosine, tryptophan, phenylalanine). Millan's teste (Millon-Nasse reaction) : - Tyrosinedeg (phenol group of tyrosine). Therefore millon's test is positive in tyrosinosisdeg. Aldehyde test : - Tryptophan (indole ring) Hopkins-tole reaction : - Tryptophan (indole ring) Sakaguch's reaction : - Arginine (guanidinium group of arginine). Sulphur test : - Cysteine (sulphydryl group) Nitroprusside test : - Cysteine (sulphydryl group) Pauly's test : - Histidine (imidazole group) Biuret reaction : - Peptide bond Diazo reaction Q (Pauli's) : - Histidine or tyrosine.