What are telomeres and their role in aging and cancer?

• A. Telomeres are mutation hotspots that drive cancer progression.
• B. Telomeres code for aging proteins.
• C. Telomeres are enzymes that synthesize DNA.
• D. Telomeres protect chromosome ends; shorten with replication; telomerase activity in cancer cells extends telomeres.

Answer: (D)

Telomeres are protective caps of repetitive DNA at the ends of chromosomes. Each time a cell divides, the DNA replication machinery can’t fully copy the chromosome ends, so telomeres shorten. Over many divisions, shortened telomeres act like a clock: once they become too short, the cell typically stops dividing or undergoes programmed death, linking telomere length to aging at the cellular level. In many cancers, an enzyme called telomerase is reactivated, adding back telomere repeats and extending chromosome ends, which lets cancer cells keep dividing and growing unchecked. This blend—telomeres shrinking with replication and telomerase extending them in cancer cells—explains their roles in aging and cancer. Telomeres themselves aren’t mutation hotspots, they don’t code for aging proteins, and they aren’t enzymes that synthesize DNA.