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When the lagging strand is being replicated on the original strand, the 5'-3' pattern must be used; thus a small discontinuity occurs and an Okazaki Fragment forms. These fragments are processed by the replication machinery to produce a continuous strand of DNA and hence a complete daughter DNA helix.
In dealing with the synthesis of complementary DNA strands the nascent leading strand always reads 5' to 3'. Its antiparallel complement strand, the nascent lagging strand reads from 3' to 5'. Because the original strands of DNA are antiparallel, and only one continuous new strand can be synthesised at the 3' end of the leading strand due to the intrinsic 5'-3' polarity of DNA polymerases, the other strand must grow discontinuously in the opposite direction. Regarding the lagging strand, the result of this strand's discontinuous replication is the production of a series of short sections of DNA called Okazaki fragments. Experimental Proof: Each Okazaki fragment is initiated near the replication fork at an RNA primer created by primase, and extended by DNA polymerase III. In eukaryotes, lagging strand synthesis is carried out by the DNA polymerase δ. The primer is later removed by enzymes that have endonucleolytic activity such as Ribonuclease H (RNAse H), flap endonucleases (FENs) and Dna2 helicase/nucleases. In prokaryotes the FEN nuclease is a domain of DNA polymerase I while in eukaryotes FENs are separate enzymes. The excised RNA bases are replaced with DNA by DNA polymerase I in prokaryotes or DNA polymerase δ in eukaryotes. Adjoining fragments are then linked together by DNA ligase, using phosphodiester bonds, to create a continuous strand of DNA.
McGraw Hill Higher Education article discussing DNA synthesis
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Okazaki_fragment". A list of authors is available in Wikipedia.|