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Monday, December 15, 2008

Okasaki Fragments are seen during the synthesis of ds DNA

Question 31
Okasaki Fragments are seen during the synthesis of
a.       ds DNA
b.      ss DNA
c.       m RNA
d.      t RNA
a. ds DNA
Harper 26th Edition Page 328, 27.335
Lippincott 3rd Edition Page 403
Thinker and TRAP !!!
Repeat, but with a slightly different stem
An 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. It was originally discovered in 1968 by Reiji Okazaki, Tsuneko Okazaki, and their colleagues while studying replication of bacteriophage DNA in Escherichia coli.
The polymerase III holoenzyme (the dnaE gene product in E.Coli) binds to template DNA as part of a multiprotein complex that consists of several polymerase accessory factors (beta, gamma, delta, delta’ and theta). DNA polymerases only synthesize DNA in the 5’ to 3’ direction and only one of the several different types of polymerases is involved at the replication fork. Because the DNA Strands are antiparallel, the polymerase functions asymmetrically. On the leading (Forward) strand, the DNA is synthesized continuously.
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. On the lagging (retrograde) strand, the DNA is systhesized in short (1-5kb) fragments, the so called Okazaki fragments. These fragments are processed by the replication machinery to produce a continuous strand of DNA and hence a complete daughter DNA helix.
Please note that synthesis of lagging strand involves DNA polymerase I, but the Okasaki fragments of the lagging strands are synthesized by DNA polymerase III
Gap Filling and synthesis of lagging strand
DNA Proofreading and repair
DNA repair
Mitochondrial DNA synthesis
Processive leading strand synthesis
Reiji Okazaki  was a Japanese molecular biologist known for his research in DNA replication and especially for describing the role of so-called Okazaki fragments which he discovered working with his wife Tsuneko Okazaki in 1968.

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