Cell cycle and apoptosis · USMLE Step 1

Which of the following proteins is a key tumor suppressor that regulates both cell-cycle checkpoints and apoptosis in response to DNA damage?

  1. Cyclin B
  2. CDK2
  3. p53
  4. Cyclin A
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Correct answer: p53

p53 acts as a tumor suppressor, inducing cell cycle arrest at checkpoints (e.g., G1/S or G2/M) to allow DNA repair; if damage is irreparable, p53 can also trigger apoptosis to prevent propagation of mutated cells.

Difficulty: Medium Question 5 of 19

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