Question

Which structural feature distinguishes proline from other natural $\alpha$-amino acids :

• A. It is optically inactive
• B. It contains aromatic group
• C. It is dicarboxylic acid
• D. It has a secondary amine
• E. It contains two amino groups

Answer 1

The correct option is D It has a secondary amine

Proline is the only proteinogenic amino acid whose side-group links to the -amino group and, thus, is also the only proteinogenic amino acid containing a secondary amine at this position.