Question

Explain in detail (use a drawing to support you explanation), why after each round of replication, the new daughter strand is ~20nucleotide’s shorter than the parent strand.

Answer 1

In DNA relication, every RNA primer synthesized during replication can be removed and replaced with DNA strand except the RNA primer at the 5 end of the newly synthesized strand. This small section of RNA can only be removed, not replaced with DNA.Enzymes Rnase H and FEN1 remove RNA primer, but DNA polymerase will add new DNA only if the DNA polymerase has an existing strand 5¹ to it to extand.However, there is no more DNA in the 5¹ direction after the final RNA primer. So DNA polymerase cannot replace the RNA with DNA. Therefore, both daugther DNA strands have an incomplete 5¹ stand with 3¹ overhang.

In the absence of additional cellular processes, Nucleases would digest these single strand 3¹ overhangs. each daugther DNA would become shorter then the parental DNA. and eventually entaire DNA would be lost. To revent this shortening the ends of linear eukaryotic chromosomes have special structures called Telomerases.