Question

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

Short answer

Answer: The amino acid responsible for the synthesis of serotonin and melatonin is tryptophan. The biosynthesis of serotonin involves hydroxylation and decarboxylation reactions, while the biosynthesis of melatonin involves acetylation and methylation reactions.

Step-by-step solution

Identify the amino acid responsible for serotonin and melatonin synthesis

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

Explain the conversion of tryptophan to serotonin

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.

Explain the conversion of serotonin to melatonin

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.

Key concepts

Tryptophan

Tryptophan is an essential amino acid that plays a crucial role in the biosynthesis of serotonin and melatonin. Our body cannot produce tryptophan on its own, so we must obtain it from dietary sources such as turkey, chicken, and milk. Once ingested, tryptophan is involved in various metabolic pathways, one of which leads to the production of serotonin and subsequently melatonin. These molecules are vital for regulating mood, sleep, and wakefulness cycles.
Tryptophan's involvement in serotonin and melatonin synthesis highlights the importance of this amino acid in maintaining mental health and circadian rhythms.

• Essential amino acid
• Obtained through diet
• Precursor for serotonin and melatonin
• Influences mood and sleep regulation

Hydroxylation and Decarboxylation

The conversion of tryptophan to serotonin is a two-step process involving hydroxylation and decarboxylation reactions. These biochemical transformations are crucial for producing serotonin, a neurotransmitter important in regulating mood and behavior.

Hydroxylation Reaction
In the first step, tryptophan is converted into 5-hydroxytryptophan (5-HTP) by the enzyme tryptophan hydroxylase. This process is known as hydroxylation, where a hydroxyl group (-OH) is added to the tryptophan molecule. Tryptophan hydroxylase is a rate-limiting enzyme, meaning it controls the speed of serotonin production.

Decarboxylation Reaction
Following hydroxylation, 5-HTP undergoes decarboxylation, a process where a carboxyl group (-COOH) is removed. This reaction is catalyzed by the enzyme aromatic L-amino acid decarboxylase, resulting in the production of serotonin, also known as 5-hydroxytryptamine (5-HT).
These reactions are not only essential for serotonin production but also critical in the regulation of neurotransmitter levels in the brain. Maintaining proper levels of serotonin is necessary for healthy brain function and emotional well-being.

Acetylation and Methylation

The pathway from serotonin to melatonin in the brain involves acetylation and methylation, which are essential modifications in the production of melatonin. Melatonin regulates our sleep-wake cycle, often referred to as the circadian rhythm.

Acetylation Reaction
The first step in melatonin synthesis from serotonin involves the enzyme serotonin N-acetyltransferase. This enzyme adds an acetyl group (-COCH3) to serotonin, forming N-acetylserotonin. This process is called acetylation, and it primarily occurs in the pineal gland in the brain.

Methylation Reaction
The final step is catalyzed by the enzyme hydroxyindole O-methyltransferase (HIOMT), which adds a methyl group (-CH3) to N-acetylserotonin, converting it to melatonin. This reaction, known as methylation, completes the biosynthesis of melatonin.
These chemical modifications ensure that melatonin is efficiently produced and released in response to changes in light, helping regulate daily sleep patterns and promoting restful sleep.