How does DNA replication take place?

DNA replication takes place by semi-conservative replication (i.e. only half of the strand in each DNA molecule are from the original DNA molecule). First, the enzyme DNA helices is required to break the hydrogen bonds between the bases on the original DNA strand, which makes the strands unwind to form two single strands. Each individual strand acts then as a template for a new strand. Complementary base pairings mean that free floating DNA nucleotides are attracted to their complementary exposed bases on each original template strand - A with T and C with G. Condensation reactions join the nucleotides of the new strands together catalysed by the enzyme DNA polymerase. Hydrogen bonds form between the bases on the original and new strands. Each new DNA molecule contains one strand from the original DNA molecule and one new strand.