An amino acid under certain conditions have both positive and negative charges simultaneously in the same molecule. Such a form of amino acid is called

Options

A. acidic form
B. basic form
C. aromatic form
D. Zwitterion

Answer

D

Explanation

`underset("Zwitterion (isoelectric pH)")(R-underset(NH_(3)^(+))underset(|)overset(H)overset(|)(C)-COO^(-))`
In neutral solution, an amino acid molecule exists as a dipolar ion (zwitter ion), i.e., molecule containing positive and negative groups. The charge on the ion changes with `pH`. In an acidic solution (low `pH`) the amino acid picks up `H^(+)` ions and becoms positively charged. In alkaline solution (high `pH`) the amino acid donates `H^(+)` ions to 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 the isoelectric `pH`.