Question

Which amino acid contains secondary amino groups in its structure?
A. Proline
B. Glycine
C. Alanine
D. Lysine

Answer 1

Hint: Amino acids contain both amine and an acid in their structures. That is why they are called amino acids. Maximum amino acids contain primary amines in their structures. Very few amino acids contain secondary amines in their structures.

Complete step by step answer:
- The general structure of the amino acids is as follows.

- Here R = H or alkyl group.
- The R group decides the name of the amino acid.
- To know which amino acid has secondary amine in its structure among the given options we should draw the structures of the all amino acids in the given options.
- Coming to given options, option A, Proline. The structure of proline is as follows.

- Coming top option B, Glycine. The structure of Glycine is as follows.

- Coming to option C, Alanine. The structure of Alanine is as follows.

- Coming to option D, Lysine. The structure of Lysine is as follows.

- Primary amine means the amino group contains at least two hydrogen with nitrogen.
- Secondary amine means the amino group contains one hydrogen on nitrogen.
- By observing all the above structures we can easily identify the secondary amine which is present in proline.
- The amine group is involved in the cyclic ring.
- Therefore Proline is the amino acid containing secondary amine in its structure.

- So, the correct option is A.

Note: Because of the presence of an amino group in the cyclic structure proline is called ‘imino acid’. Lysine is one of the amino acids containing two primary amine groups in its structure and it is an essential amino acid.