During DNA replication, the enzyme DNA helicase separates the two strands by breaking the hydrogen bonds between bases of each strand. Activated DNA nucleotides hydrogen bond with the exposed complementary bases of the template strand, in the pairs adenine (A) & thymine (T), and guanine (G) & cytosine (C). The enzyme DNA polymerase forms the sugar-phosphate backbone of the new strand by creating phosphodiester bonds between the adjacent nucleotides.DNA replication is semi-conservative because each daughter molecule contains one DNA strand that is newly-synthesised, and one that is from the parent molecule.(Could include labelled diagram to illustrate points)