Okazaki fragments - Wikipedia, the free encyclopedia

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** Okazaki fragments **

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*Okazaki fragments* are short, newly synthesized DNA fragments that are
formed on the lagging template strand during DNA replication. They are
complementary to the lagging template strand, together forming short
double-stranded DNA sections. Okazaki fragments are between 1,000 and 2,000
nucleotides long in /Escherichia coli/ and are 150 nucleotides long in
eukaryotes. They are separated by ~10-nucleotide RNA primers and are
unligated until RNA primers are removed, followed by enzyme ligase
connecting (ligating) the two Okazaki fragments into one continuous newly
synthesized complementary strand.

On the leading strand DNA replication proceeds continuously along the DNA
molecule as the parent double-stranded DNA is unwound, but on the lagging
strand the new DNA is made in installments, which are later joined together
by a DNA ligase enzyme. This is because the enzymes that synthesise the new
DNA can only work in one direction along the parent DNA molecule. On the
leading strand this route is continuous, but on the lagging strand it is
discontinuous.^[1]

DNA is synthesised from 5' to 3', thus when copying the 3' to 5' strand,
replication is continuous. Phosphodiester links form between the 3' to 5'
and nucleotides can be added with the aid of the enzyme DNA polymerase for
the continuous leading strand. However, in order to synthesise the lagging
strand (the replication fork which is travelling in the opposite direction)
synthesis occurs in small sections (100-200 nucleotides at a time in
eukaryotes). These new stretches of DNA are called Okazaki fragments and
each one requires its own RNA primer.

Okazaki fragments were originally discovered in 1966 by Kiwako Sakabe, and
Reiji Okazaki during their research on DNA replication of /Escherichia


Source: en.wikipedia.org/wiki/Okazaki_fragments

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