A molecule that carries both a positive as well as a negative charge
What is Zwitterion?
Zwitterion comprises two (or more) functional groups. One of the functional groups carries a positive charge and another one carries a negative charge. Thus, the net charge of such a molecule is zero and it is electrically neutral as the presence of the opposite charges in the same molecule balances each other. Amino acid is an excellent example of zwitterions.
It comprises functional groups: an amino group (positive) and a carboxylate group (negative), alongside a side chain group (R group). Amino acid is in a zwitterionic state at a pH of 2.2 to 9.4, and therefore with a net zero charge.
However, when the pH is decreased below 2.2, the amino acid would have a net charge of +1 as the carboxylic group becomes neutral. When the pH is increased above 9.47, the amino acid would have a net charge of -1 as the amino group becomes neutral and the negative carboxylic group is predominant.