Q.47 Which of the following chemical messenger(s) is/are derivative(s) of
tryptophan?
(A) γ-amino butyric acid
(B) Indole acetic acid
(C) Melatonin
(D) Serotonin

Tryptophan serves as a precursor for key chemical messengers like serotonin and melatonin through specific biosynthetic pathways. This MCQ tests knowledge of amino acid derivatives central to neuroscience and plant biology.

Correct Answer

The correct options are (B) Indole acetic acid, (C) Melatonin, and (D) Serotonin.​

Option Explanations

• (A) γ-Amino Butyric Acid (GABA): Derived from glutamate via decarboxylation by GAD enzyme, not from tryptophan; functions as primary inhibitory neurotransmitter.​

• (B) Indole Acetic Acid (IAA): Plant auxin hormone synthesized from tryptophan pathway involving indole-3-pyruvic acid; regulates growth and tropisms.​

• (C) Melatonin: Pineal gland hormone from serotonin (tryptophan → 5-HTP → serotonin → N-acetylserotonin → melatonin); regulates circadian rhythms.​​

• (D) Serotonin (5-HT): Neurotransmitter formed via tryptophan hydroxylase to 5-HTP then decarboxylase; modulates mood, sleep, and gut function.​

Biosynthetic Pathways

Tryptophan undergoes hydroxylation and decarboxylation for serotonin production, with further acetylation and methylation yielding melatonin. In plants, tryptophan converts to IAA via multiple routes like IPyA pathway. GABA pathway remains glutamate-specific, unrelated to indole ring of tryptophan.​​