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 benzene and pyrrole ring structure, a key functional group in some biomolecules.
Analyzing the amino acids:
Alanine: Features a —CH₃ side chain; it lacks any rings.
Tryptophan: Contains a —CH₂—indole side chain; the indole structure is its defining characteristic.
Glycine: Possesses the simplest side chain, —H; no ring is present.
Proline: Includes a five-membered pyrrolidine ring, not an indole group.
Consequently, only Tryptophan incorporates an indole group in its side chain.