Final answer:
The end replication problem occurs mainly on the lagging strand due to discontinuous synthesis. The leading strand is synthesized continuously towards the replication fork, while telomerase helps address the issue on the lagging strand in eukaryotic cells.
Step-by-step explanation:
The end replication problem is observed mainly on the lagging strand and not on the leading strand during DNA replication. DNA polymerase requires a primer with a free 3' hydroxyl group to initiate nucleotide addition, and because of this, short fragments called Okazaki fragments are synthesized on the lagging strand, which is synthesized discontinuously and in the direction away from the replication fork. In contrast, the leading strand is synthesized continuously, in the direction toward the replication fork, therefore bypassing the end replication problem which is encountered by the lagging strand near the end of chromosomes.
During the termination phase of eukaryotic replication, the enzyme telomerase extends one of the two strands to avoid the shortening of DNA after each replication cycle. This enzymatic activity specifically addresses the inability of DNA polymerase to completely replicate the ends of linear chromosomes on the lagging strand template.