How do you explain the amphoteric behaviour of amino acids ?

Explanation

Amino acids contain an acidic (carboxyl group ) and a basic (amino) group within the same molecule. In aqueous solution , they neutralize each other. The carboxyl group loses a proton while the amino group accepts it. As a result, a dipolar or zwitterion is formed.
`H_(2) -underset(R)underset(|)(CH)-COOHto H_(3)overset(+)N-underset("Zwitterion")underset(R)underset(|)(CH)-COO^(-)`.
In zwitterionic form , `alpha`-amino acids show amphoteric behaviour as they react with both acids and bases. In the acidic medium , `COO^(-)` ion of the zwitterion accepts a proton to form the cation (I) while in the basic medium , `overset(+)NH_(3)` ion loses a proton to form the anion (II).
`H_(3)overset(N)-underset((I))underset(R)underset(|)CH-COOHoverset(OH^(-))underset(H^(+))hArr H_(3)overset(N)-underset("Zwitterion")underset(R)underset(|)CH-COO^(-) overset(OH^(-))underset(H^(+))hArr H_(2)N-underset(III)underset(R)underset(|)CH-COO^(-)` .
Thus, `oversetNH_(3)` group acts as the acid while `COO^(-)` group acts as the base.