C O N T E N T SSee AlsoDescriptionAn Okazaki fragment is a relatively short fragment of DNA (with an RNA primer at the 5' terminus) created on the lagging strand during DNA replication. These fragments are processed by the replication machinery to produce a continous strand of DNA and hence a complete daughter DNA helix. In dealing with the synthesis of complementary DNA strands the leading strand always reads 3' to 5'. Its antiparallel complement strand, the lagging strand reads from 5' to 3'. 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. (Remember this is a complementary strand and not an identical image). 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.
Each Okazaki fragment is initiated near the replication fork at an RNA primer created by primase, and extended by DNA polymerase III. The primer is later removed by enzymes that have nucleolytic 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. Originally discovered by Reiji Okazaki, Tsuneko Okazaki in 1968, and their colleagues while studying replication of bacteriophage DNA in Escherichia coli. Links
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