Hello! I'm Orris. How can I help you today?

From "golden notes biochemistry rapid revision handwritten notes 3rd edition , by Dr Rajesh jambulkar" write a 5 mark short note on folate trap

Reading File

Finding Sources

Reading File

Searching Images

folate trap methionine synthase vitamin B12 deficiency methyltetrahydrofolate

I now have all the content needed. Note that "Golden Notes by Dr Rajesh Jambulkar" is not in the library, but the folate trap is a standard biochemistry concept covered identically across all major textbooks (Harper's, Lippincott, etc.). Here is a complete 5-mark short note:

Short Note: Folate Trap (5 Marks)

Definition

The folate trap (also called the methyl folate trap) is a condition of functional folate deficiency caused by vitamin B12 deficiency, in which folate becomes irreversibly trapped in the form of 5-methyltetrahydrofolate (5-methyl THF) and cannot be utilized for essential biosynthetic reactions.

Biochemical Basis

The key enzyme involved is methionine synthase (5-methyl THF-homocysteine methyltransferase), a vitamin B12-dependent enzyme.

Normal reaction:

5-methyl THF + Homocysteine → THF + Methionine (requires Vitamin B12 as cofactor)

Dietary folates and folates released from cells enter the circulation primarily as 5-methyl THF.
The only way 5-methyl THF can be converted back to free THF (the active form) is via methionine synthase.
The reduction of methylenetetrahydrofolate → methyltetrahydrofolate (by MTHFR) is irreversible.

Mechanism of the Trap

In Vitamin B12 deficiency:

Methionine synthase is impaired (B12 is its coenzyme).
5-methyl THF cannot donate its methyl group to homocysteine.
5-methyl THF accumulates and cannot be converted to THF.
Folate is effectively "trapped" in a form that is metabolically useless.
Result: Functional folate deficiency, despite normal or even elevated serum folate levels.

Consequences

Effect	Mechanism
Megaloblastic anemia	THF is needed (as N5,N10-methylene THF) for dUMP → dTMP conversion (thymidylate synthesis); deficiency impairs DNA synthesis in rapidly dividing cells (bone marrow)
Hyperhomocysteinemia	Homocysteine cannot be remethylated to methionine; homocysteine accumulates
Impaired purine synthesis	THF-dependent one-carbon units needed for purine ring synthesis are unavailable
Subacute combined degeneration of spinal cord	Due to methionine deficiency in CNS (failure of methylation of myelin basic protein); NOT corrected by folate

Clinical Significance

Pernicious anemia: Caused by autoimmune destruction of parietal cells → lack of intrinsic factor → B12 malabsorption → folate trap → megaloblastic anemia.
Masking B12 deficiency: Giving folic acid to a B12-deficient patient will bypass the folate trap (providing free THF directly), correcting megaloblastic anemia but NOT the neurological damage - a dangerous clinical pitfall.
Homocysteine as a biomarker: Elevated plasma homocysteine signals impaired methionine synthase activity and is a risk factor for atherosclerosis and thrombosis.

Diagram Summary

Dietary Folates
      ↓
5-methyl THF  ──── [Methionine synthase + Vit B12] ──→  THF (active)
                              ↑
                         Homocysteine ──────────────→  Methionine

In B12 deficiency:
5-methyl THF accumulates → FOLATE TRAP → Functional folate deficiency
                                        ↓
                              Megaloblastic anemia + Hyperhomocysteinemia

Sources: Harper's Illustrated Biochemistry 32nd Ed., p. 556-557; Basic Medical Biochemistry - A Clinical Approach 6e.

This is a shared conversation. Sign in to Orris to start your own chat.