Neoplasia: p53 and the cell cycle: practice question

A Pathology 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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Pathology · Neoplasia: p53 and the cell cycle

Sample item

A normal fibroblast with intact p53 is exposed to a low dose of ionising radiation that causes repairable DNA damage. Which sequence best describes the p53 response?

Ap53 is degraded by MDM2 so the cell moves quickly into S phaseBATM activation stabilises p53, which induces p21 and halts the cell in G1 for repairCp53 phosphorylates Rb so E2F is released and DNA synthesis beginsDp53 activates telomerase so the cell can divide indefinitely

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

The answer and the reasoning

B. ATM activation stabilises p53, which induces p21 and halts the cell in G1 for repair

DNA damage activates ATM kinase, which phosphorylates and stabilises p53 by blocking MDM2-mediated degradation. p53 transcribes p21, an inhibitor of cyclin-CDK complexes, causing G1 arrest while repair occurs. If damage is irreparable, p53 induces apoptosis through BAX and PUMA.

Option by option

A. p53 is degraded by MDM2 so the cell moves quickly into S phase
MDM2-mediated degradation describes p53 in an undamaged cell, not after damage.
B. ATM activation stabilises p53, which induces p21 and halts the cell in G1 for repair (correct)
ATM-mediated stabilisation and p21-induced G1 arrest is the protective response of intact p53.
C. p53 phosphorylates Rb so E2F is released and DNA synthesis begins
Rb phosphorylation is performed by cyclin D-CDK4 and cyclin E-CDK2 complexes, which p21 inhibits.
D. p53 activates telomerase so the cell can divide indefinitely
p53 does not activate telomerase; telomerase reactivation is a feature of cancer cells and not a p53 response.

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 Pathology question

What is the answer to this Pathology question?

The best answer is B, ATM activation stabilises p53, which induces p21 and halts the cell in G1 for repair. DNA damage activates ATM kinase, which phosphorylates and stabilises p53 by blocking MDM2-mediated degradation.

Why is "p53 is degraded by MDM2 so the cell moves quickly into S phase" not the answer?

MDM2-mediated degradation describes p53 in an undamaged cell, not after damage.

Why is "p53 phosphorylates Rb so E2F is released and DNA synthesis begins" not the answer?

Rb phosphorylation is performed by cyclin D-CDK4 and cyclin E-CDK2 complexes, which p21 inhibits.

Why is "p53 activates telomerase so the cell can divide indefinitely" not the answer?

p53 does not activate telomerase; telomerase reactivation is a feature of cancer cells and not a p53 response.

What concept does this question test?

It tests Neoplasia: p53 and the cell cycle in Pathology. p53 transcribes p21, an inhibitor of cyclin-CDK complexes, causing G1 arrest while repair occurs. If damage is irreparable, p53 induces apoptosis through BAX and PUMA.

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 Neoplasia: p53 and the cell cycle?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology 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.