Epigenetics: DNA methylation and azacitidine: practice question

A Biochemistry question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

Try it

Biochemistry · Epigenetics: DNA methylation and azacitidine

Sample item

A 72-year-old man with myelodysplastic syndrome is given azacitidine, a hypomethylating agent. Which principle explains why it can be effective?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. It inhibits DNA methyltransferase, reversing promoter CpG methylation that silences tumour suppressor genes

Methylation of cytosine in CpG islands at promoters recruits proteins that compact chromatin and repress transcription. In myelodysplastic syndrome, tumour suppressor genes are often silenced this way. Azacitidine and decitabine are cytosine analogues incorporated into DNA that trap DNA methyltransferase, so methylation falls and gene expression can resume.

Option by option

  • A. It inhibits thymidylate synthase and starves cells of thymidine

    Thymidylate synthase inhibition is the action of fluorouracil, and is not how azacitidine works.

  • B. It inhibits DNA methyltransferase, reversing promoter CpG methylation that silences tumour suppressor genes (correct)

    Trapping DNA methyltransferase leads to demethylation and gene reactivation.

  • C. It intercalates into DNA and blocks topoisomerase II

    Topoisomerase II inhibition is the action of agents such as etoposide and anthracyclines.

  • D. It inhibits histone deacetylase and compacts chromatin

    Histone deacetylase inhibition is the action of vorinostat and does not describe azacitidine.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

More Biochemistry questions

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, It inhibits DNA methyltransferase, reversing promoter CpG methylation that silences tumour suppressor genes. Methylation of cytosine in CpG islands at promoters recruits proteins that compact chromatin and repress transcription.

Why is "It inhibits thymidylate synthase and starves cells of thymidine" not the answer?

Thymidylate synthase inhibition is the action of fluorouracil, and is not how azacitidine works.

Why is "It intercalates into DNA and blocks topoisomerase II" not the answer?

Topoisomerase II inhibition is the action of agents such as etoposide and anthracyclines.

Why is "It inhibits histone deacetylase and compacts chromatin" not the answer?

Histone deacetylase inhibition is the action of vorinostat and does not describe azacitidine.

What concept does this question test?

It tests Epigenetics: DNA methylation and azacitidine in Biochemistry. In myelodysplastic syndrome, tumour suppressor genes are often silenced this way. Azacitidine and decitabine are cytosine analogues incorporated into DNA that trap DNA methyltransferase, so methylation falls and gene expression can resume.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Epigenetics: DNA methylation and azacitidine?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.