During DNA Replication, the existing molecule gets replicated, resulting in two semi-conservative DNA molecules. The enzyme helicase unwinds and unzips the double helix of the DNA, while topoisomerase moves ahead of helicase, relieving the strain and tension of this action, and single-stranded binding proteins prevent the strands from rewinding. As the double helix is being unwinded, DNA primase adds short RNA primers two both of the separated strands. On the leading strand, DNA polymerase III adds free nucleotides based on complimentary base pairing ( Adenine & Thymine; Guanine & Cytosine) in a 5' to 3' direction, forming a continuous new strand.On the lagging strand, DNA primase adds several RNA primers, as the movement of DNA polymerase will be in the opposite direction of helicase, due to the anti-parallel nature of DNA strands. Subsequently, DNA polymerase III adds free nucleotides to the primers, creating several short segments called Okazaki fragments. DNA polymerase I then replaces the RNA primers on both strands with DNA, followed by DNA ligase joining the Okazaki fragments together. Once replication is completed, the enzymes detach and the DNA molecules recoil.
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