Because DNA polymerase cannot extend DNA after removing the RNA primer, what happens to the telomeres with each replication cycle?

Because DNA polymerase cannot extend DNA after removing the RNA primer, what happens to the telomeres with each replication cycle?

• A. Telomeres are extended
• B. A section is lost with each replication cycle
• C. No change occurs
• D. Telomeres shorten then lengthen alternately

Answer: (B)

The end replication problem is being tested here. On the lagging strand, DNA is built in fragments starting from RNA primers. When those RNA primers are removed, there’s no primer available at the very end for DNA polymerase to extend from, so the final segment of the chromosome isn’t replicated. As a result, a small piece of the telomere is lost with each round of replication. Telomeres are protective repeats at chromosome ends, so this gradual loss acts like a cellular clock, shortening telomeres over time in most somatic cells. Telomeres would be extended only if active telomerase were present to add repeats back to the ends, which isn’t the case for most ordinary somatic cells. The option that suggests no change isn’t correct because the end-replication problem guarantees a loss each cycle. The idea of alternating shortening and lengthening isn’t the typical pattern, though some cells can lengthen telomeres via telomerase in certain contexts.

The end replication problem is being tested here. On the lagging strand, DNA is built in fragments starting from RNA primers. When those RNA primers are removed, there’s no primer available at the very end for DNA polymerase to extend from, so the final segment of the chromosome isn’t replicated. As a result, a small piece of the telomere is lost with each round of replication. Telomeres are protective repeats at chromosome ends, so this gradual loss acts like a cellular clock, shortening telomeres over time in most somatic cells.

Telomeres would be extended only if active telomerase were present to add repeats back to the ends, which isn’t the case for most ordinary somatic cells. The option that suggests no change isn’t correct because the end-replication problem guarantees a loss each cycle. The idea of alternating shortening and lengthening isn’t the typical pattern, though some cells can lengthen telomeres via telomerase in certain contexts.