Replikaationhaarassa

Replikaationhaarassa, often referred to as the replication fork, is a Y-shaped structure that forms during DNA replication. It is the site where the double-stranded DNA molecule unwinds, allowing each strand to be used as a template for the synthesis of a new complementary strand. This unwinding is carried out by enzymes called helicases, which break the hydrogen bonds between the complementary base pairs.

At the replication fork, two new DNA strands are synthesized simultaneously: the leading strand and the lagging strand. The leading strand is synthesized continuously in the 5' to 3' direction, following the movement of the replication fork. This is possible because DNA polymerase can add nucleotides to the 3' end of the growing strand.

In contrast, the lagging strand is synthesized discontinuously in short fragments called Okazaki fragments. This is because DNA polymerase can only synthesize DNA in the 5' to 3' direction, and the lagging strand template runs in the opposite direction relative to the replication fork's movement. Primase, an enzyme, lays down RNA primers to initiate the synthesis of each Okazaki fragment. DNA polymerase then extends these primers, and later, another DNA polymerase removes the RNA primers and fills the gaps with DNA nucleotides. Finally, DNA ligase joins the Okazaki fragments together to form a continuous strand.

The accurate and timely formation and progression of the replication fork are crucial for maintaining the integrity of the genome and ensuring proper cell division. Errors or disruptions at this site can lead to mutations and genetic instability.