DNA Replication (Medical Entrance)

DNA pol III is the first polymerase to participate in DNA replication. 

DNA pol I fills the necessary nucleotides at gaps formed by excision of RNA primer between the okazaki fragments.

The proofreading function of DNA polymerase I is carried out by a 3' to 5' exonuclease. 

DNA chain growth occurs in 5' to 3' direction. 

Arthur Kornberg is credited for the discovery of DNA pol I in 1956.

DNA replication starts when helicase unzips DNA helix.............ssBP stabilises the unwound strands..............primase synthesises RNA primer...........and then, polymerase carries out the synthesis.

The AT base pairs have only two hydrogen bonds, which are easy to unzip. Therefore, AT-rich sequences act as origin of DNA replication.

DNA polymerase catalyses the elongation of the leading strand.

 The 5′ end of the nicked strand is transferred to a tyrosine residue on the nuclease and the free 3′ OH group is used by the DNA polymerase to synthesise the new strand.

DNA gyrase moves ahead of DNA helicase, removing the torques which come in the way.

Primase adds RNA primer to enable replication of DNA.

It polymerises DNA from a template of RNA.

Primasome is a complex of primase with DNA helicase.

Semi-conservative model replicates DNA only as DNA has two strands which can act template for synthesis of new DNA.

During DNA replication, topoisomerase regulates the overwinding or underwinding of DNA.