Proteins - ISC Class 12 Chemistry Questions with Answers, Page 2

Glycine in zwitter ion form: $\mathrm{{}^+H_3N-CH_2-COO^-}$, the dipolar ion formed when the $\mathrm{-COOH}$ proton transfers to the $\mathrm{-NH_2}$ group.

Amino acids contain both an acidic carboxyl group ($-\mathrm{COOH}$) and a basic amino group ($-\mathrm{NH_2}$). The $-\mathrm{COOH}$ transfers a proton to $-\mathrm{NH_2}$ to form a dipolar ion (zwitterion) $\mathrm{H_3N^+-CHR-COO^-}$. In acid, the $-\mathrm{COO^-}$ accepts a proton, so it acts as a base; in alkali, the $-\mathrm{NH_3^+}$ loses a proton, so it acts as an acid. Hence amino acids are amphoteric.