What is the role of telomeres in aging and cell division?

• A. They lengthen with every division
• B. They shorten with division, limiting replication
• C. They are unchanged by division
• D. They prevent transcription

Answer: (B)

Telomere length acts as a mitotic clock, shortening with each cell division and limiting how many times a cell can divide. During DNA replication, the ends of linear chromosomes can’t be copied completely, so a small portion of the telomere is lost with every division—the end-replication problem. As divisions accumulate, telomeres become critically short, triggering cellular senescence or apoptosis and contributing to aging at the tissue level.

Some cells, like germ cells and many stem cells, as well as most cancer cells, can maintain telomere length through telomerase or alternative lengthening mechanisms, which is why they can divide more times. But in most ordinary somatic cells, telomeres progressively shorten, which is the main link to aging and the finite capacity for cell division.

The other options don’t fit: telomeres do not generally lengthen with division in normal cells, they are not unchanged by division, and they don’t primarily prevent transcription.