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a: template, b: leading strand, c: lagging strand, d: replication fork, e: primer, f: Okazaki fragments Many enzymes are involved in the DNA replication fork. The replication fork is a structure that forms within the long helical DNA during DNA replication.
After around 20 nucleotides, elongation is taken over by Pol ε on the leading strand and Pol δ on the lagging strand. [103] Polymerase δ (Pol δ): Highly processive and has proofreading, 3'->5' exonuclease activity. In vivo, it is the main polymerase involved in both lagging strand and leading strand synthesis. [104]
This asymmetry is due to the formation of the replication fork and its division into nascent leading and lagging strands. The leading strand is synthesized continuously and in juxtapose to the leading strand; the lagging strand is replicated through short fragments of polynucleotide (Okazaki fragments) in a 5' to 3' direction. [6]
Priming enzymes, (which are DNA-dependent RNA polymerases), solve this problem by creating an RNA primer on the leading and lagging strands. The leading strand is primed once, and the lagging strand is primed approximately every 1000 (+/- 200) base pairs (one primer for each Okazaki fragment on the lagging strand).
The leading strand is continuously synthesized and is elongated during this process to expose the template that is used for the lagging strand (Okazaki fragments). During the process of DNA replication, DNA and RNA primers are removed from the lagging strand of DNA to allow Okazaki fragments to bind to.
DNA polymerase III will then synthesize a continuous or discontinuous strand of DNA, depending if this is occurring on the leading or lagging strand (Okazaki fragment) of the DNA. DNA polymerase III has a high processivity and therefore, synthesizes DNA very quickly.
For eukaryotes specifically, the mechanism of DNA replication elongation between the leading and lagging strand differs. On the lagging strand, nicks exist between Okazaki fragments and are easily recognizable by the DNA mismatch repair machinery prior to ligation. Due to the continuous replication that occurs on the leading strand, the ...
DNA polymerase I removes the primer, replacing it with DNA, and DNA ligase joins the ends to make another molecule of double-stranded circular DNA. As a summary, a typical DNA rolling circle replication has five steps: [2] Circular dsDNA will be "nicked". The 3' end is elongated using "unnicked" DNA as leading strand (template); 5' end is ...