Metabolites of tryptophan can give rise to:
**Core Concept**
The question pertains to the metabolic pathway of tryptophan, an essential amino acid involved in various physiological processes. Tryptophan is a precursor to several important metabolites, including serotonin, melatonin, and niacin.
**Why the Correct Answer is Right**
Tryptophan is converted into 5-hydroxytryptophan (5-HTP) by the enzyme tryptophan hydroxylase in the brain. 5-HTP is then converted into serotonin (5-hydroxytryptamine) by the enzyme aromatic L-amino acid decarboxylase. Serotonin is a key neurotransmitter involved in mood regulation, appetite, and sleep-wake cycles. It also serves as a precursor to melatonin, a hormone that regulates the sleep-wake cycle.
**Why Each Wrong Option is Incorrect**
* **Option A:** While tryptophan is an essential amino acid, it is not directly converted into acetylcholine.
* **Option B:** Niacin is synthesized from tryptophan, but it is not a direct metabolite of tryptophan.
* **Option D:** Dopamine is synthesized from tyrosine, not tryptophan.
**Clinical Pearl / High-Yield Fact**
Tryptophan depletion can lead to decreased serotonin levels, contributing to symptoms of depression and anxiety. This is why some antidepressants, such as selective serotonin reuptake inhibitors (SSRIs), target the serotonin system to improve mood regulation.
**Correct Answer:** C.