How do Okazaki fragments contribute to DNA replication?

Okazaki fragments contribute to DNA replication by enabling the synthesis of the lagging strand in a discontinuous manner.

In the process of DNA replication, the two strands of the DNA molecule are separated and each serves as a template for the synthesis of a new complementary strand. This process is carried out by an enzyme called DNA polymerase. However, DNA polymerase can only add nucleotides in one direction, from 5' to 3'. This means that while one strand (the leading strand) can be synthesised continuously, the other strand (the lagging strand) cannot.

This is where Okazaki fragments come into play. Named after the Japanese scientists who discovered them, Okazaki fragments are short sequences of DNA nucleotides (approximately 1000 base pairs in prokaryotes and 100-200 in eukaryotes) which are synthesised discontinuously on the lagging strand. The synthesis of these fragments begins with the creation of a short RNA primer, which is then extended by DNA polymerase.

Once an Okazaki fragment has been synthesised, the RNA primer at the start of the fragment is removed and replaced with DNA by another enzyme, DNA polymerase I in prokaryotes and RNase H in eukaryotes. The gaps between the fragments are then sealed by an enzyme called DNA ligase, creating a continuous DNA strand.

In this way, Okazaki fragments enable the synthesis of the lagging strand in the 5' to 3' direction, despite the fact that the overall direction of replication on this strand is 3' to 5'. This ensures that both strands of the DNA molecule are accurately replicated, maintaining the integrity of the genetic information and allowing it to be passed on to the next generation of cells.