Question

An amino acid under certain conditions has both positive and negative charges simultaneously in the same molecule. Such a form of amino acid is called
A) Acidic form
B) Basic form
C) Aromatic form
D) Zwitterionic form

Answer 1

Hint: When an amino acid is integrated into a polypeptide the charges on the amino and the carboxyl groups fade away. Among the 20 common amino acids molecules five have a side chain which can be charged.

Complete answer:
The charged amino acids are simple to allocate. They are composed of two basic residues, lysine and arginine both of them having positive charge at neutral pH values and also two acidic consisting aspartate and glutamate two of carrying negative charge at neutral pH.
A zwitterion is a molecule with functional groups of which at least one has a positive and one has a negative electrical charge. The net charge of entire molecule is zero

In neutral solution, an amino acid molecule exists as a dipolar ion (zwitterion) i.e; molecule containing positive and negative ionic groups. The charge present on the ion changes with pH. In an acidic solution (low Ph) the amino acid picks up H+ ions and becomes 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 of the molecules as a zwitterion is called the isoelectric Ph. When an amino acid dissolves in water, the zwitter ions interact with H2O molecules- acting as both an acid and a base. But unlike simple amphoteric compounds that may only form either a cationic or anionic species, zwitterions simultaneously have both ionic states.

Hence, the correct answer is option (D)

Note: Amino acids contain an amine group (basic) and a carboxylic group (acidic). The $NH_2$ group is a stronger base, and so it picks up H+ from the –COOH group to leave a zwitterion (i.e; the amino group deprotonated the carboxylic acid)