Question

Which of these amino acids contains an indole group?

• A. Alanine
• B. Tryptophan
• C. Glycine
• D. Proline

Hint:

Tryptophan is the only standard amino acid whose side chain contains an indole ring, making it both aromatic and a significant UV-absorbing amino acid.

Answer 1

The Correct Option is B

An indole group is a fused ring structure composed of a six-membered benzene ring joined to a five-membered nitrogen-containing pyrrole ring. It is a key functional group found in certain biomolecules.
Let us examine each of the given amino acids: 
Alanine: Has a side chain —CH₃; it does not contain any ring, aromatic or otherwise. 
Tryptophan: Has a side chain —CH₂—indole. The indole structure is a defining feature of tryptophan. 
Glycine: Has the simplest side chain —H; no ring present.
Proline: Contains a five-membered ring, but it is a pyrrolidine ring (not an indole group). 
Therefore, among the options, only Tryptophan contains an indole group in its side chain.