Biological substances

1. BIOLOGICAL SUBSTANCE
1.5-HT
2.Melatonin
3.Dopamine
4.Noradrenaline
5.Adrenaline
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3. Serotonin pathway
• Serotonin or 5-hydroxytryptamine (5HT):
Neurotransmitter, synthesized from tryptophan.
• About 1% of the tryptophan is converted to
serotonin.
• Synthesis: Serotonin is synthesized in the
intestinal cells.
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4. Step 1
• Tryptophan is hydroxylated at 5th carbon.
• Tryptophan  5-Hydroxytryptophan by
“tryptophan hydroxylase”.
• Tryptophan Hydroxylase requires
tetrahydrobiopterin as a cofactor.
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5. Step 2
• 5-Hydroxytryptophan is decarboxylase to give
serotonin.
• 5-Hydroxytryptophan Serotonin by aromatic
amino acid decarboxylase (PLPdependent)
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7. Degradation of serotonin:
• Monoamine oxidase (MAO) degrades
serotonin to 5- hydroxyindoleacetate (5HIA)
which is excreted in urine.
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8. Functions of serotonin :
Serotonin is a neurotransmitter and performs a variety of
functions.
1. Powerful vasoconstrictor resulting smooth muscle
contraction in bronchioles and arterioles.
2. It is closely involved in the regulation of cerebral activity.
3. It controls the behavioural patterns, sleep, blood pressure
and body temperature.
4. Evokes the release of peptide hormones from
gastrointestinal tract.
5. Necessary for peristalsis.
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10. Melatonin pathway
Melatonin: Hormone synthesized by the pineal
gland.
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11. Steps
• Serotonin  N-acetylserotonin by “serotonin N-
acetylase”
• N-acetylserotonin  melatonin by “N-
Acetylserotonin O-methyltransferase” in
presence of S-adenosylmethionine
• Synthesis and secretion of melatonin from pineal
gland is controlled by light
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12. Pathway continued
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13. Pathway continued
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15. Functions of melatonin
1. Involved in circadian rhythms or diurnal variations of
the body. It plays a significant role in sleep and wake
process.
2. It inhibits the production of melanocyte stimulating
hormone (MSH) and adrenocorticotropic hormone
(ACTH).
3. It has some inhibitory effect on ovarian functions.
4. Melatonin also performs a neurotransmitter function.
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