In this prologue, the cell replicates it's DNA inside the nucleolus. As the cell grows bigger, it needs more nutrients and space in order to survive. Before undergoing mitosis, DNA replication has to happen first.
ACT 1: Initiation
An enzyme called Helicase, unwinds the double helix DNA molecule and separates the strands; this also breaks the hydrogen bonding between nitrogenous bases. SSBP (Single-strand binding proteins) stabilize the DNA strands and this creates replication bubbles. As tension builds up during the unwinding, DNA Gyrase enzymes cuts the DNA in order to release the tension. RNA Primase enzymes place RNA Primers to signal Polymerase III to begin replicating the strands.
ACT 2: Elongation
DNA Polymerase III synthesizes the new DNA from a 5' to 3' direction and adds free nucleotides to the 3' direction. Since DNA is an anti parallel structure, the two new strands will have to grow in an opposite direction. A new strand of DNA called "the leading strand" replicates continuously using a 3' to 5' so that it will become 5' to 3' with the template. Another new strand of DNA is called "the lagging strand" replicates discontinuously as RNA Primase comes in and synthesizes a short RNA Primer, which will be extended by DNA polymerase III to form sections called Okazaki Fragments; the leading strand replicates in an opposite direction with the lagging strand.
Act 3: Termination
DNA Lygase enzyme acts as a glue and joins each Okazaki fragment together. Phosphodiester bonds are created between DNA Lygase and Okazaki fragments. DNA Polymerase I comes in and proofreads the newly synthesized strands and replaces the RNA Primer with DNA. At last the two new DNA molecules separate from each other.
DNA Replication is now complete!
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