DNA replication is the process by which DNA makes a copy of itself before cell division, ensuring each new cell receives identical genetic information. This process is called semiconservative because each new DNA molecule consists of one original and one newly synthesized strand.

DNA helicase unwinds the double helix by breaking hydrogen bonds between base pairs, separating the two DNA strands. Each separated strand then acts as a template for free nucleotides to bind, forming complementary pairs. DNA polymerase then catalyzes the formation of phosphodiester bonds, building the sugar-phosphate backbones of the two new DNA strands. This results in two identical DNA molecules.

DNA polymerase always moves in the 5' to 3' direction. Due to the antiparallel nature of DNA strands, one new strand, the leading strand, can be synthesized continuously in the same direction as the unwinding helix. However, the other new strand, the lagging strand, must be synthesized in short fragments called Okazaki fragments, in the opposite direction of the unwinding. DNA ligase then joins these fragments to complete the lagging strand.