DNA helicase unzips and unwinds the DNA double helix by breaking hydrogen bonds between complementary base pairs. This exposes the bases on two strands creating template strands. Free floating nucleotides are attracted to the exposed bases and bond to them via complementary base pairing (adenine-thymine and guanine-cytosine). DNA polymerase then joins the new nucleotides together in a series of condensation reactions forming phosphodiester bonds in the sugar-phosphate bakcbone.Two new DNA strands are made, each with one old strand and one new one therefore DNA is said to be replicated semi-conservatively.