Primer (molecular Biology) - Mechanism in Vivo

Mechanism in Vivo

Further information: DNA replication#The replication fork

The lagging strand is that strand of the DNA double helix that is orientated in a 5' to 3' manner. Therefore, its complement must be synthesized in a 3'→5' manner. Because DNA polymerase III cannot synthesize in the 3'→5' direction, the lagging strand is synthesized in short segments known as Okazaki fragments. Along the lagging strand's template, primase builds RNA primers in short bursts. DNA polymerases are then able to use the free 3'-OH groups on the RNA primers to synthesize DNA in the 5'→3' direction.

The RNA fragments are then removed by DNA polymerase I for prokaryotes or DNA polymerase δ for eukaryotes (different mechanisms are used in eukaryotes and prokaryotes) and new deoxyribonucleotides are added to fill the gaps where the RNA was present. DNA ligase then joins the deoxyribonucleotides together, completing the synthesis of the lagging strand.