Final answer:
The lagging strand of DNA faces challenges during replication as it gets progressively shorter with each cell division due to the inability to replace the RNA primer at the very end with DNA nucleotides. Telomerase resolves this by extending the chromosome ends, allowing DNA polymerase to complete the strand.
Step-by-step explanation:
During DNA replication, problems arise when replicating the ends of the lagging strand at chromosomes. On the lagging strand, DNA synthesis occurs in short segments known as Okazaki fragments that are initially started with RNA primers.
These primers are necessary because DNA polymerases cannot start synthesis without a free 3' hydroxyl group to add nucleotides to. Normally, these RNA primers are replaced by DNA nucleotides, but at the very end of the chromosome, there is no upstream DNA where a primer can be laid down for the replacement.
Therefore, with each cell division, the lagging strand would get progressively shorter as these terminal RNA primers cannot be replaced with DNA.
This issue is resolved by the enzyme telomerase, which extends the ends of chromosomes, providing a template for DNA polymerase to fill in the complementary DNA strand and thereby prevent the chromosome from shortening.