Okazaki fragments

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 named after the Japanese scientist Reiji Okazaki, who first discovered them.

Discovery

Reiji Okazaki and his team of researchers at the University of Nagoya in Japan discovered Okazaki fragments in 1968. They were studying the mechanism of DNA replication in Escherichia coli, a type of bacteria. The discovery of Okazaki fragments provided crucial evidence supporting the theory that DNA replication is a discontinuous process on the lagging strand.

Structure and Formation

Okazaki fragments are typically between 1,000 to 2,000 nucleotides long in Eukaryotes, and approximately 100-200 nucleotides long in Prokaryotes. They are formed because the lagging strand that is being used as a template for replication has its 3' end facing away from the replication fork. This means that DNA polymerase, the enzyme that synthesizes new DNA, cannot add nucleotides in the direction of replication.

The formation of Okazaki fragments begins with the synthesis of a short RNA primer by the enzyme Primase. This primer serves as a starting point for DNA polymerase, which begins adding nucleotides, forming the Okazaki fragment. Once an Okazaki fragment has been synthesized, the RNA primer is removed and replaced with DNA by the enzyme DNA polymerase I in prokaryotes and Pol δ in eukaryotes. The fragments are then joined together by the enzyme DNA ligase to form a continuous DNA strand.

Role in DNA Replication

The discovery of Okazaki fragments confirmed that DNA replication is a discontinuous process on the lagging strand. This is because DNA polymerase can only synthesize DNA in a 5' to 3' direction, but the lagging strand is oriented in a 3' to 5' direction at the replication fork. Therefore, replication on the lagging strand occurs in short bursts, producing Okazaki fragments.

The formation of Okazaki fragments is a crucial step in DNA replication, as it allows the replication of the lagging strand to occur in the same overall direction as replication of the leading strand. This ensures that the entire DNA molecule is accurately and efficiently replicated.

See Also

• DNA replication
• Reiji Okazaki
• DNA polymerase
• Primase
• DNA ligase

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