Explain the mechanism by which DNA is replicated

DNA is replicated by semi-conservative replication meaning that each double stranded DNA molecule replicates to form two new double stranded molecules - each with one original and one new strand. This occurs in a series of steps...DNA helicase unwinds and unzips the DNA molecule by breaking the hydrogen bonds between nucleotide bases - separating the two strands. Free DNA nucleotides line up against the exposed nucleotides according to complementary base pairing (A&C and G&T). The free nucleotides and strands are joined together by DNA polymerase - creating 2 identical DNA molecules.