Telomeres Regulate Cell Division Limits

Steps:

• Telomeres shorten with each DNA replication due to the end-replication problem.
• In most cells, progressive shortening triggers senescence when telomeres reach a critical length.
• Cancer and stem cells maintain telomere length via telomerase enzyme.
• Evaluate options: A matches senescence mechanism; others misstate telomere function or repair.

Why A is correct:

• Telomere shortening acts as a molecular clock, leading to the Hayflick limit where critically short telomeres induce p53-mediated cell cycle arrest, halting division.

Why the others are wrong:

• B: Longer telomeres delay senescence, slowing aging; adding them would extend cell lifespan.
• C: Telomeres are maintained by telomerase, a reverse transcriptase, not RNA polymerase.
• D: Telomeres cap ends to prevent fusion or degradation but do not broadly prevent DNA damage.

Final answer: A