DNA repair: 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 · DNA repair

Sample item

A 35-year-old man has early-onset colorectal cancer with a strong family history and microsatellite instability. Which DNA repair pathway is defective?

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

The answer and the reasoning

A. Mismatch repair

Hereditary non-polyposis colorectal cancer (Lynch syndrome) is caused by germline defects in mismatch repair genes such as MLH1 and MSH2. Replication errors persist in repetitive sequences, producing microsatellite instability.

Option by option

  • A. Mismatch repair (correct)

    Correct. Failure to fix replication mismatches gives microsatellite instability and Lynch syndrome.

  • B. Non-homologous end joining

    Non-homologous end joining repairs double-strand breaks and is not linked to microsatellite instability.

  • C. Nucleotide excision repair

    Defective nucleotide excision repair causes xeroderma pigmentosum with skin cancers after UV exposure.

  • D. Base excision repair

    Base excision repair removes single damaged bases and is not the cause of Lynch syndrome.

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 A, Mismatch repair. Hereditary non-polyposis colorectal cancer (Lynch syndrome) is caused by germline defects in mismatch repair genes such as MLH1 and MSH2.

Why is "Non-homologous end joining" not the answer?

Non-homologous end joining repairs double-strand breaks and is not linked to microsatellite instability.

Why is "Nucleotide excision repair" not the answer?

Defective nucleotide excision repair causes xeroderma pigmentosum with skin cancers after UV exposure.

Why is "Base excision repair" not the answer?

Base excision repair removes single damaged bases and is not the cause of Lynch syndrome.

What concept does this question test?

It tests DNA repair in Biochemistry. Replication errors persist in repetitive sequences, producing microsatellite instability.

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 DNA repair?

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.