Which statement best describes the end-replication problem?

Which statement best describes the end-replication problem?

• A. Telomeres shorten with each replication
• B. Telomeres lengthen with each replication
• C. Telomeres remain unchanged
• D. Telomeres are transferred to sister chromatids

Answer: (A)

The end-replication problem comes from the fact that DNA polymerase can only synthesize DNA in the 5' to 3' direction and needs an RNA primer. On the linear chromosomes, the last segment on the lagging strand cannot be fully copied once the RNA primer at the very end is removed, so the final portion remains unreplicated. This means telomeres—the end caps of chromosomes—shorten with each round of replication. Over time, this shortening limits how many times a cell can divide in most somatic cells, acting like a cellular clock. In cells with active telomerase, telomeres can be lengthened, but that’s not the typical outcome in most body cells. Therefore, the description that telomeres shorten with each replication best captures the end-replication problem.

The end-replication problem comes from the fact that DNA polymerase can only synthesize DNA in the 5' to 3' direction and needs an RNA primer. On the linear chromosomes, the last segment on the lagging strand cannot be fully copied once the RNA primer at the very end is removed, so the final portion remains unreplicated. This means telomeres—the end caps of chromosomes—shorten with each round of replication. Over time, this shortening limits how many times a cell can divide in most somatic cells, acting like a cellular clock. In cells with active telomerase, telomeres can be lengthened, but that’s not the typical outcome in most body cells. Therefore, the description that telomeres shorten with each replication best captures the end-replication problem.