Question

Amino acids generally exist in the form of Zwitterions. This means they contain :

• A. basic $-{NH}_2$ group and acidic $-COOH$ group
• B. the basic $-\stackrel{+}{N}{H}_3$ group and acidic $-{COO}^{-}$ group
• C. basic $-{NH}_2$ and acidic $-H^{+}$ group
• D. basic $-{COO}^{-}$ group and acidic $-\stackrel{+}{N}{H}_3$ group

Answer 1

Answer: (D)

Basic ${-COO}^{-}$ group and acidic $-\stackrel{+}{N}{H}_3$ group

A zwitterion is a compound with no overall electrical charge, but which contains separate parts which are positively and negatively charged. In aqueous solution, the carboxyl group can lose a proton (becomes basic group) and amino group can accept a proton (becomes acidic) giving rise to the dipolar ion known as Zwitterions.

$\underset{\text{amino acid}}{H_{2}N-CH\left(R\right)-COOH}\rightleftharpoons \underset{Zwitterion}{H_3\stackrel{+}{N}-CH\left(R\right)-{COO}^{-}}$