Okazaki fragment

Okazaki fragments are short, newly synthesized DNA fragments that are formed on the lagging strand during DNA replication. They are complementary to the lagging template strand, together forming short double-stranded DNA sections. Okazaki fragments are named after the Japanese scientist Reiji Okazaki, who first discovered them.

Discovery

Reiji Okazaki and his wife, Tsuneko Okazaki, discovered Okazaki fragments in the late 1960s. They were studying the replication of bacteriophage DNA in Escherichia coli when they noticed that the newly synthesized DNA was initially produced as short fragments. These fragments were later linked together to form a continuous DNA strand.

Formation

During DNA replication, the DNA polymerase can only add nucleotides in the 5' to 3' direction. On the leading strand, replication occurs continuously, but on the lagging strand, replication must occur in the opposite direction. This is accomplished by synthesizing short fragments of DNA, known as Okazaki fragments.

Each Okazaki fragment is initiated by the enzyme RNA primase, which synthesizes a short RNA primer. This primer serves as a starting point for the DNA polymerase, which extends the fragment by adding nucleotides. Once an Okazaki fragment has been extended as far as possible, the RNA primer is removed and replaced with DNA by the enzyme DNA polymerase I. The fragments are then joined together by the enzyme DNA ligase to form a continuous DNA strand.

Role in DNA replication

Okazaki fragments play a crucial role in DNA replication, allowing the DNA polymerase to synthesize the lagging strand in the necessary 5' to 3' direction. Without Okazaki fragments, the replication of the lagging strand would not be possible.

See also

• DNA replication
• Leading strand
• Lagging strand
• DNA polymerase
• RNA primase
• DNA ligase

References

Okazaki fragment Resources
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