RNA processing: 5-prime cap: 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 · RNA processing: 5-prime cap

Sample item

A laboratory transcribes an mRNA in vitro for expression in human cells, but without any 5-prime modification. The mRNA is degraded quickly and translated poorly. Which modification restores stability and ribosome recruitment?

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

The answer and the reasoning

B. A 7-methylguanosine cap joined by a 5-prime to 5-prime triphosphate linkage

Eukaryotic mRNA is capped co-transcriptionally with 7-methylguanosine through an unusual 5-prime to 5-prime triphosphate bond. The cap protects against 5-prime exonucleases and is bound by eIF4E to recruit the small ribosomal subunit. The poly-A tail is a separate 3-prime modification.

Option by option

  • A. A Shine-Dalgarno sequence upstream of AUG

    The Shine-Dalgarno sequence is used by prokaryotic ribosomes, not eukaryotic ones.

  • B. A 7-methylguanosine cap joined by a 5-prime to 5-prime triphosphate linkage (correct)

    Correct. The cap protects the mRNA and recruits initiation factors.

  • C. A CCA trinucleotide at the 3-prime end

    CCA is added to the 3-prime end of tRNA, not mRNA.

  • D. A poly-A tail added to the 5-prime end

    The poly-A tail is at the 3-prime end and binds poly-A binding protein.

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, A 7-methylguanosine cap joined by a 5-prime to 5-prime triphosphate linkage. Eukaryotic mRNA is capped co-transcriptionally with 7-methylguanosine through an unusual 5-prime to 5-prime triphosphate bond.

Why is "A Shine-Dalgarno sequence upstream of AUG" not the answer?

The Shine-Dalgarno sequence is used by prokaryotic ribosomes, not eukaryotic ones.

Why is "A CCA trinucleotide at the 3-prime end" not the answer?

CCA is added to the 3-prime end of tRNA, not mRNA.

Why is "A poly-A tail added to the 5-prime end" not the answer?

The poly-A tail is at the 3-prime end and binds poly-A binding protein.

What concept does this question test?

It tests RNA processing: 5-prime cap in Biochemistry. The cap protects against 5-prime exonucleases and is bound by eIF4E to recruit the small ribosomal subunit. The poly-A tail is a separate 3-prime modification.

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 RNA processing: 5-prime cap?

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.