Many organic substances are negatively charged e.g., acetic acid, while others are positively charged e.g., ammoniumion. An aminoacid under certain conditions would have both positive and negative charges simultaneously in the same molecule. Such a form of aminoacid is called

Options

A. Positively charged form
B. Negatively charged form
C. Neutral form
D. Zwitterionic form

Answer

D

Explanation

In neutral solution an amino acid molecule exists as a dipolar ion i.e. molecule containing positive and negative ionic groups. The charge on the ion changes with pH. In an acidic solution the amino acid picks up `H^(+)` ions and becomes positively charged. In alkaline solution, the amino acid donates `H^(+)` ions into the medium and becomes negatively charged. The pH at which the amino acid is electrically neutral or the molecule exists as a zwitterion is called isoelectric pH.