GATE 2021 BT – Question 47

Which chemical messengers are derivatives of tryptophan?

Show answer and explanation

Correct answer: (B) Indole acetic acid; (C) Melatonin; (D) Serotonin

Explanation

**Tryptophan** is an aromatic amino acid with an indole ring, and it is the precursor of several signalling molecules:

**Indole acetic acid (IAA):** the main plant auxin, made from tryptophan. ✓
**Serotonin (5-hydroxytryptamine):** made by hydroxylation and decarboxylation of tryptophan. ✓
**Melatonin:** made from serotonin, so it also derives from tryptophan. ✓
**γ-Aminobutyric acid (GABA):** made by decarboxylation of **glutamate**, not tryptophan. ✗

Answer **B, C and D**.