Question

How do you explain the amphoteric behaviour of amino acids?

Answer 1

Amino acids have both acidic (carboxyl) group and basic (amino) group in the same molecule. In the aqueous solution the carboxyl group losses proton while amino group accepts that proton. This results to fomation of zwitter ion.
This zwitter ionic form of $$\alpha$$ amino acid shows amphoteric behaviour, i.e. act both as acid and base.