Describe the process of semi-conservative DNA replication.

Semi-conservative replication is the process of making two molecules of DNA from one DNA molecule, each containing one original DNA strand and one newly synthesised DNA strand. The original double helix is unwound, and DNA helicase breaks the hydrogen bonds between complementary base pairs. Both of the seperated polynucleotide strands are used as templates. Free nucleotides then bond by complementary base pairing to their respective nucleotides on the original strands. Adenine to Thymine and Cytosine to Guanine, forming new hydrogen bonds. Adjacent nucleotides then join by phosphodiester bonds in a condensation reaction catalysed by the enzyme DNA polymerase. The final product is two copies of the original DNA molecule.