Question

Why is replicating the tips of linear chromosomes problematic and how does the cell overcome this challenge?

a) The tips contain repetitive DNA sequences that are prone to degradation; cells use telomerase to extend telomeres.
b) Linear chromosomes have fragile ends that break easily; cells repair them using DNA ligase.
c) Replication of telomeres causes mutations; cells repair these mutations using excision repair mechanisms.
d) Linear chromosomes do not face challenges during replication; they are easily duplicated by the cell machinery.

Answer 1

The replication of linear chromosome tips is problematic because the standard DNA replication machinery cannot replicate the very ends, leading to shorter chromosomes with each division. The enzyme telomerase helps to maintain these ends by extending the lagging strand, ensuring that chromosome integrity is preserved.

Step-by-step explanation:

Replicating the tips of linear chromosomes, also known as telomeres, is problematic because during DNA replication, the DNA polymerase enzyme can only add nucleotides in one direction. On the leading strand, DNA synthesis continues until the end of the chromosome is reached, but on the lagging strand, there is no place to anchor a primer for the last fragment, leading to progressively shorter telomeres after each cell division. Cells overcome this challenge using the enzyme telomerase, which contains a built-in RNA template that extends the 3′ end of the lagging strand, allowing DNA polymerase to complete the synthesis and replicate the ends of the chromosomes.