It is now well established that DNA Replication occurs semi conservatively, copying each strand of DNA separately, to produce two new DNA double helices. Each is composed of an old(Parent) strand and a newly synthesized one.
Meselson and Stahl in 1958 and J.Cairns in 1963 experimentally verified that the DNA of E.coli replicates semi conservative manner. J.H.Taylor confirmed semi conservative replication of DNA in Vicia faba chromosomes in1963.
Steps
|
Prokaryotic cells
 |
Eukaryotic cells
 |
| Unwinding of DNA double helix at replication origins(s) | Helicase (Requires ATP) | Helicase (Requires ATP) |
| Stabilization of unbound template strands | Single strand binding protein (SSB) | Single strand binding protein (SSB) |
| Synthesis of DNA leading strand lagging strand (Okazaki fragment) | DNA polymerase III DNA polymerase III | DNA polymerase delta DNA polymerase alpha |
| Removal of RNA primers | DNA polymerase I( 5’-exonuclease) | Unknown |
| Replacement of RNA with DNA | DNA polymerase I | Unknown |
| Joining of okazaki fragments | DNA ligase I (Requires NAD) | DNA ligase I (Requires ATP) |
| Removal of supercoils ahead of advancing replication forks | Topoisomerase II (DNA gyrase) (Inhibited by nalidixic acid, norfloxacin) | Topoisomerase II (Inhibited by etoposide, teniposide |
| Synthesis of telomers | Not required | Telomerase |
