Tumour suppressors: p53 in Li-Fraumeni syndrome: 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 · Tumour suppressors: p53 in Li-Fraumeni syndrome

Sample item

A girl develops an osteosarcoma at 10 years of age. Her mother had breast cancer at 32 and her maternal uncle had a sarcoma at 25. A germline TP53 mutation is identified. What is the normal role of p53 that explains the cancer predisposition?

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

The answer and the reasoning

D. It halts the cell cycle at G1/S through p21 after DNA damage, allowing repair or apoptosis

p53 is a transcription factor stabilised after DNA damage because MDM2 no longer targets it for degradation. It induces p21, which inhibits cyclin-CDK complexes and arrests the cell in G1, and induces repair genes or apoptosis if damage is irreparable. Loss of one allele in the germline (Li-Fraumeni syndrome) leaves only one hit needed for tumours such as sarcomas, breast cancer and brain tumours.

Option by option

  • A. It joins BCR to ABL and drives proliferation

    BCR-ABL is a fusion oncoprotein of chronic myeloid leukaemia.

  • B. It phosphorylates Rb to allow entry into S phase

    Phosphorylation of Rb is performed by cyclin D-CDK4/6 and promotes, rather than prevents, cell cycle entry.

  • C. It repairs mismatched bases after replication

    Mismatch repair is performed by MSH and MLH proteins, which are mutated in Lynch syndrome.

  • D. It halts the cell cycle at G1/S through p21 after DNA damage, allowing repair or apoptosis (correct)

    Damage-induced arrest or apoptosis protects against mutation accumulation.

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 D, It halts the cell cycle at G1/S through p21 after DNA damage, allowing repair or apoptosis. p53 is a transcription factor stabilised after DNA damage because MDM2 no longer targets it for degradation.

Why is "It joins BCR to ABL and drives proliferation" not the answer?

BCR-ABL is a fusion oncoprotein of chronic myeloid leukaemia.

Why is "It phosphorylates Rb to allow entry into S phase" not the answer?

Phosphorylation of Rb is performed by cyclin D-CDK4/6 and promotes, rather than prevents, cell cycle entry.

Why is "It repairs mismatched bases after replication" not the answer?

Mismatch repair is performed by MSH and MLH proteins, which are mutated in Lynch syndrome.

What concept does this question test?

It tests Tumour suppressors: p53 in Li-Fraumeni syndrome in Biochemistry. It induces p21, which inhibits cyclin-CDK complexes and arrests the cell in G1, and induces repair genes or apoptosis if damage is irreparable. Loss of one allele in the germline (Li-Fraumeni syndrome) leaves only one hit needed for tumours such as sarcomas, breast cancer and brain tumours.

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 Tumour suppressors: p53 in Li-Fraumeni syndrome?

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.