Скачать или смотреть S-Adenosylmethionine (SAM) Cycle Made Easy 🧠 | Synthesis, Utilization & Regeneration Explained

Welcome to this Biochemistry Lecture on “S-Adenosylmethionine (SAM) Cycle”, explained as per the latest edition of U. Satyanarayana Biochemistry.
In this video, we simplify the SAM cycle — its synthesis, utilisation, and regeneration, highlighting its role as the universal methyl group donor in human metabolism.

The S-Adenosylmethionine (SAM) cycle, also known as the Methionine Cycle, connects methylation reactions, amino acid metabolism, and vitamin-dependent pathways in one elegant biochemical loop.

📘 In this lecture, you will learn:

1️⃣ What is SAM (S-Adenosylmethionine)?

A biologically active methyl donor formed from Methionine and ATP.

Synthesised by the enzyme Methionine Adenosyltransferase in the liver.

Participates in over 40 methylation reactions in the body.

2️⃣ Steps of the SAM Cycle:

Step 1 – Formation:
Methionine + ATP → S-Adenosylmethionine (SAM)
(Enzyme: Methionine Adenosyltransferase)

Step 2 – Methyl Group Donation:
SAM donates its methyl group to acceptor molecules, forming S-Adenosylhomocysteine (SAH).
(Methyl transfer reactions catalysed by methyltransferases)

Step 3 – Regeneration:
SAH → Homocysteine + Adenosine (Enzyme: SAH Hydrolase)
Homocysteine → Methionine (Enzyme: Methionine Synthase, requires Vitamin B₁₂ & Folate)

Thus, the cycle continues — maintaining methyl balance and methionine homeostasis.

3️⃣ Major Methylation Reactions Using SAM:

Epinephrine synthesis: Norepinephrine → Epinephrine

Creatine synthesis: Guanidinoacetate → Creatine

Phosphatidylcholine synthesis: Phosphatidylethanolamine → Phosphatidylcholine

DNA and Protein methylation: Gene regulation

Melatonin synthesis: N-Acetylserotonin → Melatonin

4️⃣ Vitamins & Cofactors Involved:

Vitamin B₁₂ (Cobalamin) – for methionine regeneration

Folic acid (THF) – provides methyl groups.

Vitamin B₆ (Pyridoxine) – required for the transsulfuration pathway

5️⃣ Clinical Significance:

Defects or deficiencies in the SAM cycle cause:

Hyperhomocysteinemia → risk of Atherosclerosis, Thrombosis, Heart Disease

Reduced methylation capacity → affects DNA repair, neurotransmitter synthesis, and detoxification.

Supplemental SAM is used in depression, liver disorders, and arthritis therapy.

📚 Reference Textbook:
U. Satyanarayana & U. Chakrapani – Biochemistry (Latest Edition)

💡 Perfect For:
MBBS | BDS | Nursing | Pharmacy | Allied Health Sciences | NEET PG | Biochemistry Students

🎯 Focus Areas:
Methyl Group Transfer | Methionine Cycle | Clinical Biochemistry | Vitamin Metabolism

✨ Learning Outcome:
By the end of this video, you will understand the complete SAM Cycle, its biochemical significance, cofactors involved, and clinical relevance in methylation reactions and cardiovascular health.

#SAMCycle #SAdenosylmethionine #BiochemistryLecture #USatyanarayana #MethionineMetabolism #MethylationBiochemistry #ClinicalBiochemistry #MedicalBiochemistry #MBBSBiochemistry #MethylGroupDonor

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