replikaatiohaarukkat

Replikaatiohaarukkat, often translated as replication fork, refers to the Y-shaped structure that forms during DNA replication. This structure is the site where the double-stranded DNA molecule separates into two single strands, serving as a template for the synthesis of new complementary strands. The process is initiated by enzymes called helicases, which unwind the DNA helix, breaking the hydrogen bonds between complementary base pairs.

As the helicase moves along the DNA, the unwound strands are stabilized by single-strand binding proteins to prevent them from re-annealing. DNA polymerase enzymes then bind to the separated strands and begin synthesizing new DNA. This synthesis occurs in a unidirectional manner, meaning that new DNA is only added in the 5' to 3' direction. Because the two parental DNA strands are antiparallel, one new strand, the leading strand, is synthesized continuously in the same direction as the replication fork's movement.

The other new strand, the lagging strand, is synthesized discontinuously in short fragments called Okazaki fragments. This is because DNA polymerase can only synthesize in the 5' to 3' direction, and the lagging strand template runs in the opposite direction relative to the fork's progression. Primase enzymes lay down RNA primers to initiate the synthesis of each Okazaki fragment. DNA polymerase then extends these primers with DNA nucleotides. Finally, DNA ligase joins these fragments together to form a continuous lagging strand. The coordinated action at the replication fork ensures the accurate duplication of the entire genome.