Molecular biology: epigenetic regulation: 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.

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Biochemistry · Molecular biology: epigenetic regulation

Sample item

A patient with cutaneous T cell lymphoma receives vorinostat, an inhibitor of histone deacetylases. What is the effect of increased histone lysine acetylation on chromatin?

AAdded positive charge tightens chromatin and silences genesBNeutralised positive charge loosens DNA-histone contact, making chromatin accessible for transcriptionCNucleosomes are cleaved into linker DNADCytosine in CpG islands becomes methylated

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

The answer and the reasoning

B. Neutralised positive charge loosens DNA-histone contact, making chromatin accessible for transcription

Acetylation of lysine tails neutralises their positive charge, weakening interaction with the negatively charged DNA backbone. Chromatin becomes more open (euchromatin) and transcription factors gain access, so expression of genes such as tumour suppressors may be restored. Deacetylation promotes compact, silenced chromatin.

Option by option

A. Added positive charge tightens chromatin and silences genes
Acetylation removes, not adds, positive charge, and it opens chromatin.
B. Neutralised positive charge loosens DNA-histone contact, making chromatin accessible for transcription (correct)
Correct. Acetylation relaxes chromatin and favours transcription.
C. Nucleosomes are cleaved into linker DNA
Acetylation does not cleave nucleosomes.
D. Cytosine in CpG islands becomes methylated
CpG methylation is done by DNA methyltransferases and is a different mechanism.

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.

Questions about this Biochemistry question

What is the answer to this Biochemistry question?

The best answer is B, Neutralised positive charge loosens DNA-histone contact, making chromatin accessible for transcription. Acetylation of lysine tails neutralises their positive charge, weakening interaction with the negatively charged DNA backbone.

Why is "Added positive charge tightens chromatin and silences genes" not the answer?

Acetylation removes, not adds, positive charge, and it opens chromatin.

Why is "Nucleosomes are cleaved into linker DNA" not the answer?

Acetylation does not cleave nucleosomes.

Why is "Cytosine in CpG islands becomes methylated" not the answer?

CpG methylation is done by DNA methyltransferases and is a different mechanism.

What concept does this question test?

It tests Molecular biology: epigenetic regulation in Biochemistry. Chromatin becomes more open (euchromatin) and transcription factors gain access, so expression of genes such as tumour suppressors may be restored. Deacetylation promotes compact, silenced chromatin.

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 Molecular biology: epigenetic regulation?

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.