How do you explain amphoteric nature of amino acids?

Explanation

As `alpha`- amino acids contain both an acidic (carboxyl gp) and basic (amino group) within same molecule. In aqueous solution they neutralise each other i.e. carboxyl group loses a proton and amino group accepts. As a result zwitter ion is fanned.
Now zwitter ion reacts with acid as well as with base i.e. it shows amphoteric nature.