Molecular biology and genetics: nonsense-mediated mRNA decay: 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 · Molecular biology and genetics: nonsense-mediated mRNA decay

Sample item

A patient is homozygous for a single-base change that creates an early stop codon in a gene. Cells contain very little mRNA from this gene. Which cellular process explains the low transcript level?

ARho-dependent termination of transcription before the gene is copiedBSilencing of the transcript by microRNA-guided RNA interferenceCNonsense-mediated decay of mRNAs carrying a premature stop codonDReduced histone acetylation at the promoter of this particular gene

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

The answer and the reasoning

C. Nonsense-mediated decay of mRNAs carrying a premature stop codon

A premature termination codon upstream of an exon junction marks the mRNA for nonsense-mediated decay, a surveillance pathway that degrades faulty transcripts and prevents truncated proteins. This explains why many nonsense variants produce little mRNA and behave as null alleles.

Option by option

A. Rho-dependent termination of transcription before the gene is copied
Rho-dependent termination is a bacterial transcription mechanism.
B. Silencing of the transcript by microRNA-guided RNA interference
RNA interference is guided by small RNAs binding the transcript and is not triggered by a stop codon.
C. Nonsense-mediated decay of mRNAs carrying a premature stop codon (correct)
Correct. The surveillance pathway degrades mRNAs with premature stop codons.
D. Reduced histone acetylation at the promoter of this particular gene
Histone acetylation changes would not be caused by a single-base coding change.

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 C, Nonsense-mediated decay of mRNAs carrying a premature stop codon. A premature termination codon upstream of an exon junction marks the mRNA for nonsense-mediated decay, a surveillance pathway that degrades faulty transcripts and prevents truncated proteins.

Why is "Rho-dependent termination of transcription before the gene is copied" not the answer?

Rho-dependent termination is a bacterial transcription mechanism.

Why is "Silencing of the transcript by microRNA-guided RNA interference" not the answer?

RNA interference is guided by small RNAs binding the transcript and is not triggered by a stop codon.

Why is "Reduced histone acetylation at the promoter of this particular gene" not the answer?

Histone acetylation changes would not be caused by a single-base coding change.

What concept does this question test?

It tests Molecular biology and genetics: nonsense-mediated mRNA decay in Biochemistry. This explains why many nonsense variants produce little mRNA and behave as null alleles.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 and genetics: nonsense-mediated mRNA decay?

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.