Okazaki fragments
Okazaki fragment is called a molecular biology formed during DNA replication of the lagging strand short section of DNA and RNA. It is named after the Japanese scientist Tsuneko Okazaki and her husband Reiji Okazaki, who proposed the replication mechanism 1968. In prokaryotes, such a fragment from 1000 to 2000, 100 to 200 nucleotides long in eukaryotes.
The doubling of a DNA molecule is such that first, the two anti- parallel single strands of the double helix can be separated by the enzyme helicase, a replication fork is formed, the bidirectional ( rarely also unidirectional) continuing from its origin on the basis in the DNA molecule. In large genomes, there are in the replication of many DNA origins of replication (and thus replication forks ) so as to increase the rate of replication. The formation of the DNA in the immediate vicinity of the fork and semi- conservative, that is, at each of the two strands is initially present parents with a daughter strand complementary base sequence formed.
The responsible for the synthesis of DNA protein DNA polymerase III ( eukaryotes: DNA polymerase δ and DNA polymerase ε ) needs to jumpstart a short primer called and bound to the copy DNA RNA molecule, then what it comes to more nucleotides, the building blocks of DNA, extended. The polymerase is able to form only in the 5' -3 ' direction of a seamless new strand. The in migration direction of the replication fork continuously formed (in the picture to the left) daughter strand called leading strand ( leading beach ), the discontinuous formed at the other, extending in the 5' -3 'direction parent strand due to enzyme properties is called lagging strand ( lagging beach ).
Subsequently strand is synthesized near the fork, starting from the primer to the end of the unwound portion of DNA in the 5 ' to 3' direction, but opposite to the direction of movement of the replication fork; because the DNA winds up only at a finite speed, the resulting string is short. The fork moves continues, and other parts of the DNA are free to which a primase again sets a primer. From there, the polymerase begins to close another partial DNA until it encounters the 3 'end of the short piece preformed etc. These are short stretches of repetitive formed from DNA and RNA are called Okazaki fragments.
Another enzyme, the DNA polymerase I ( eukaryotes: DNA polymerase α ) from the primer, and fills in the gaps between the fragments with additional deoxynucleotides again. A DNA ligase, the individual fragments, so that eventually a complete DNA strand of the sequence strand is created.