JEE Advanced · 2010 · 11 Apr 2010 · Paper 1 · Biomolecules

Lysine in the given zwitterionic form has:

1. One $-{\mathrm{NH}}_2$ group (primary amine on the side chain) - basic
2. One $-{\mathrm{NH}}_3^{+}$ group (protonated α-amino group) - not basic (already protonated)
3. One $-{\mathrm{COO}}^{-}$ group (deprotonated carboxyl) - not basic

The basic groups are those that can accept protons. In this form, only the $-{\mathrm{NH}}_2$ group on the side chain and the $-{\mathrm{COO}}^{-}$ group can act as bases. However, $-{\mathrm{COO}}^{-}$ is typically considered a weak base. The question asks for basic groups, which are the amine groups capable of accepting protons.

Actually, examining the structure more carefully: the $-{\mathrm{NH}}_2$ group and the $-{\mathrm{COO}}^{-}$ group are the two basic sites. The answer is 2.