Replication fork
583541
221367265
2008-06-24T05:49:29Z
SorryGuy
397823
rvv
[[Image:Replication fork.svg|right|thumb|Scheme of the replication fork.<br>a: template, b: leading strand, c: lagging strand, d: replication fork, e: primer, f: [[Okazaki fragments]]]]
The '''replication fork''' is a structure that forms during [[DNA replication]]. It is created by [[helicase]]s, which break the [[hydrogen bond]]s holding the two DNA strands together. The resulting structure has two branching "prongs", each one made up of a single strand of DNA, that are called the leading and lagging strands. [[DNA polymerase]] creates new partners for the two strands by adding [[nucleotide]]s.
==Leading strand==
[[Image:DNA replication.svg|thumb|450px|left|DNA replication]]The '''leading strand''' is the DNA strand at the opposite side of the replication fork from the lagging strand. It goes from a 5' to 3' direction, because DNA Polymerase can only synthesize a new DNA strand in a 5' to 3' manner. On the leading strand, [[DNA polymerase III]] (DNA Pol III) "reads" the DNA and adds [[nucleotides]] to it continuously.
==Lagging strand==
The '''lagging strand''' is the DNA strand opposite the replication fork from the leading strand. It goes from a [[Directionality (molecular biology)|3' to 5']].
When replicating, the original DNA splits in two, forming two "prongs" which resemble a fork (i.e. the "[[replication fork]]"). DNA has a ladder-like structure; imagine a ladder broken in half vertically, along the steps. Each half of the ladder now requires a new half to match it.
[[Pol III]], the main [[DNA replication]] enzyme, cannot work in the [[Directionality (molecular biology)|3' to 5']] direction of the template strand, and so replication of the lagging strand is more complicated than of the leading strand.
On the lagging strand, [[primase]] "reads" the DNA and adds [[RNA]] to it in short, separated segments. DNA polymerase III lengthens the primed segments, forming [[Okazaki fragment]]s. [[DNA polymerase I]] then "reads" the fragments, removes the RNA using its [[flap endonuclease]] domain, and replaces the RNA nucleotides with DNA nucleotides (this is necessary because RNA and DNA use slightly different kinds of nucleotides). [[DNA ligase]] joins the fragments together.
==See also==
* [http://www.wehi.edu.au/education/wehi-tv/dna/replication.html More detailed replication fork animation] WEHI-TV
{{DNA replication}}
[[Category:DNA replication]]
{{genetics-stub}}
[[he:מזלג ההכפלה]]
[[pl:Widełki replikacyjne]]
[[tr:Replikasyon çatalı]]
[[zh:複製叉]]