From which amino acid is serotonin (5-HT) synthesized?

• A. Tyr
• B. Trp
• C. Phe
• D. Lys

Answer: (B)

Serotonin (5-HT) is synthesized from the amino acid tryptophan (Trp). The synthesis process involves a series of enzymatic conversions, starting with tryptophan being hydroxylated to form 5-hydroxytryptophan (5-HTP). Subsequently, 5-HTP undergoes decarboxylation to produce serotonin. Therefore, the direct precursor for serotonin is tryptophan, highlighting its critical role in the biosynthesis of this neurotransmitter.

In contrast, the other amino acids listed do not contribute to serotonin production. Tyrosine (Tyr) and phenylalanine (Phe) are precursors for other neurotransmitters, such as dopamine and norepinephrine. Lysine (Lys) is involved in various protein syntheses and metabolic pathways but does not have a role in serotonin synthesis. This distinction reaffirms the importance of tryptophan as the sole precursor for serotonin.