JEE Main · 2023 · 13 Apr 2023 · Shift 2 · Biomolecules

Every $\alpha$-amino acid carries one basic $\alpha$-amino group together with an acidic carboxyl group. In asparagine the side chain is a carboxamide, $-\mathrm{CH}{}_2-\mathrm{CONH}{}_2$, whose nitrogen lone pair is delocalised into the carbonyl and is therefore essentially non-basic, leaving only the single $\alpha$-amino group as a basic centre. Arginine, in contrast, carries a strongly basic guanidino group, lysine a basic side-chain amino group, and histidine a basic imidazole ring, each providing a second basic site. The naturally occurring amino acid with only one basic functional group is therefore asparagine.