From which amino acid are serotonin and melatonin synthesized, and what types of reactions are involved in their biosynthesis? a. b.

Serotonin and melatonin are both synthesized from the amino acid tryptophan.

The synthesis of serotonin from tryptophan involves two main reactions: 1. Tryptophan hydroxylase, which is a rate-limiting enzyme, converts tryptophan into 5-hydroxytryptophan (5-HTP). This reaction is a hydroxylation, where a hydroxyl (-OH) group is added to the tryptophan molecule. 2. Aromatic L-amino acid decarboxylase then converts 5-HTP into serotonin (5-hydroxytryptamine, 5-HT). This reaction is a decarboxylation, which removes a carboxyl (-COOH) group from the 5-HTP molecule, producing serotonin as the final product.

The synthesis of melatonin from serotonin involves two main reactions: 1. Serotonin N-acetyltransferase (NAT) catalyzes the conversion of serotonin to N-acetylserotonin. This reaction is an acetylation, in which an acetyl (-COCH3) group is added to the serotonin molecule. 2. Finally, hydroxyindole O-methyltransferase (HIOMT) catalyzes the conversion of N-acetylserotonin to melatonin. This reaction is a methylation, where a methyl (-CH3) group is added to the N-acetylserotonin molecule, resulting in the formation of melatonin as the final product. In summary, serotonin and melatonin are both synthesized from the amino acid tryptophan. The biosynthesis of serotonin involves hydroxylation and decarboxylation reactions, while the biosynthesis of melatonin involves acetylation and methylation reactions.