Molecular biology and genetics: non-homologous end joining: 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: non-homologous end joining

Sample item

An infant has severe combined immunodeficiency with absent T and B cells and marked radiosensitivity. Sequencing shows a mutation in Artemis, which is needed for V(D)J recombination. Which DNA repair pathway is impaired?

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

The answer and the reasoning

C. Non-homologous end joining of double-strand breaks

Artemis works with Ku and DNA-PK in non-homologous end joining, which also opens hairpins during V(D)J recombination. Its loss prevents antigen receptor assembly and leaves cells sensitive to ionising radiation. This explains both the immunodeficiency and the radiosensitivity.

Option by option

  • A. Mismatch repair

    Mismatch repair corrects replication errors.

  • B. Base excision repair

    Base excision repair fixes damaged single bases and is not needed for receptor assembly.

  • C. Non-homologous end joining of double-strand breaks (correct)

    Correct. NHEJ repairs double-strand breaks and opens the hairpins formed in V(D)J recombination.

  • D. Nucleotide excision repair

    Nucleotide excision repair removes bulky lesions such as thymine dimers.

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 C, Non-homologous end joining of double-strand breaks. Artemis works with Ku and DNA-PK in non-homologous end joining, which also opens hairpins during V(D)J recombination.

Why is "Mismatch repair" not the answer?

Mismatch repair corrects replication errors.

Why is "Base excision repair" not the answer?

Base excision repair fixes damaged single bases and is not needed for receptor assembly.

Why is "Nucleotide excision repair" not the answer?

Nucleotide excision repair removes bulky lesions such as thymine dimers.

What concept does this question test?

It tests Molecular biology and genetics: non-homologous end joining in Biochemistry. Its loss prevents antigen receptor assembly and leaves cells sensitive to ionising radiation. This explains both the immunodeficiency and the radiosensitivity.

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: non-homologous end joining?

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.