p53's Role in DNA Damage Checkpoint

Steps:

• p53 binds damaged DNA in interphase to halt cell cycle and prevent replication.
• Mutation from carcinogen inactivates p53, removing this checkpoint.
• Damaged DNA then replicates, accumulating mutations that promote cancer.
• Choice B matches this by stating cells with (mutated) p53 replicate damaged DNA.

Why B is correct:

• p53 is a tumor suppressor that enforces G1/S checkpoint (per cell cycle regulation); without function, damaged DNA copies during S phase, leading to genomic instability and cancer.

Why the others are wrong:

• A: p53 primarily blocks S phase replication, not mitosis directly; cells without p53 still require other signals for mitosis.
• C: The carcinogen mutates p53 gene specifically, not by accelerating division rate.
• D: Mutated p53 fails to suppress division at damage sites but does not actively cause uncontrolled division.

Final answer: B