The structural feature which distinguishes proline from other natural `alpha`-amino acids is

Options

A. It is a secondary amine
B. It is a primary amine
C. It is a tertiary amine
D. It exists as cyclic amide

Answer

A

Explanation

Proline is distinct in structure compared to other amino acids because its amino group is cyclical.
The R–group is bonded to the central carbon as well as the nitrogen atom of the amino group, forming a house – like structure.