Question

DNA replication occurs at a replication fork, which travels in both directions from the origin of replication. Describe the synthesis of DNA in both directions. What problem does the anti-parallel nature of DNA create, and how does the replication machinery solve it?

Answer 1

DNA synthesis takes place in on both strands taking as template and DNA polymerisation occur only in 5' to 3' direction by all polymerases. But during the formation of replication fork only one strand is continually exposing in 3' to 5' direction and strand formed is called leading strand. And on second strand DNA is synthesized in fragment called Okazaki fragments. A RNA primer is added to short exposed strand and DNA fragment is synthesized by DNA polymerase III in 5'-3' direction. RNA primer are then cleaved and gap is filled by RNA polymerase I. Then fragments are ligated by DNA ligase.