The process of DNA replication takes one parental DNA molecule and creates two daughter DNA molecules. This process occurs in the nucleus of the cell and occurs during the cell cycle in eukaryotic cells.
DNA replication begins with the enzyme helicase unzipping the parental DNA molecule. A fully intact DNA molecule is double-stranded and twisted to form a helix. The helix must be unwound and the hydrogen bonds between each base pair on the DNA strand must be broken for DNA replication to occur. Once the two strands are unzipped, the enzyme DNA polymerase binds to one of the strands of the DNA and begins moving up the DNA strand. As it moves, the DNA polymerase synthesizes new base pairs that are complementary to the exposed DNA base pairs. Each new base pair binds to its complementary base pair through covalent chemical bonds. As the DNA polymerase moves up the first strand of DNA, another DNA polymerase enzyme moves down the second strand of DNA. Once both DNA polymerase enzymes have reached the end of their single-stranded DNA molecules, two fully replicated, double-stranded DNA molecules exist. The two molecules are semi-conserved since they each have one strand of the parental DNA.