Question

Could you explain why progressive shortening in DNA replication occurs (possibly with a drawing of where there is no 3' end to replicate)?

Thanks

Answer 1

The Eukaryotic chromosomes are linear in shape and are associated with end replication problem. In this problem, after every round of DNA replication, the length of chromosome decreases. This occurs because of the removal of primers. Multiple primers are present on the lagging strand but a single primer is present on the leading strand. The removal of primers from the lagging strand occurs normally and there is no gap in this removal. But when primers are removed from the leading strand, then a small gap is left at the end of chromosome. This causes shortening of chromosome after every round of DNA replication and the gap is called as 3' overhang. If this continues to occur, then chromosomes will be eventually lost from the cell and the cell would die.

The problem is solved by an enzyme called telomerase which adds deoxyribonucleotides to the overhang using RNA present in itself as a template.

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