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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.
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]
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]
The lagging strand moves away from the replication fork in the 3' to 5' direction and consists of small fragments called Okazaki fragments. DNA polymerase makes the lagging strand by using a new RNA primer for each Okazaki fragment it encounters. Overall, the leading strand only uses one RNA primer, while the lagging strand uses a new RNA ...
Lagging strands, in contrast, are synthesized discontinuously: primers are placed on the template every ~200 nucleotides and extended to form short Okazaki fragments. For simplicity, this diagram does not show the replacement of primers with DNA or the synthesis of telomeres at the chromosome ends.
The dimerisation of the replicative polymerases solves the problems related to efficient synchronisation of leading and lagging strand synthesis at the replication fork, but the tight spatial-structural coupling of the replicative polymerases, while solving the difficult issue of synchronisation, creates another challenge: dimerisation of the ...
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.
Due to its high processivity, Pol δ takes over the leading and lagging strand synthesis from Pol α. [ 14 ] : 218–219 Pol δ is expressed by genes POLD1 , creating the catalytic subunit, POLD2 , POLD3 , and POLD4 creating the other subunits that interact with Proliferating Cell Nuclear Antigen (PCNA), which is a DNA clamp that allows Pol δ ...