amino acids exists as zwitterionic form.give its structure.why is it formed?

It is the property of amino acid in which they possess both positive and negative charges when placed in solutions of different pH. It results due to the neutralization reaction in amino acid. At different pH, the structures of amino acids change because of ionisable nature of −NH2 and −COOH groups. The accepted practice is to show the amino acids in the zwitterion form.

(1) The carboxyl group can lose a hydrogen ion to become negatively charged. 

(2) The amine group can accept a hydrogen ion to become positively charged.