The semi-conservative replication of DNA in terms of • breaking of hydrogen bonds between polynucleotide strands • attraction of new DNA nucleotides to exposed bases and base pairing • role of DNA helicase and of DNA polymerase.

The replication of DNA is called semi-conservative because each new piece of DNA is half old DNA and half new.

1. DNA helicase breaks the hydrogen bonds between the base pairs
2. The two strands of the DNA separate, leaving 2x polynucleotide strands
3. Free activated nucleotides are attracted to the complimentary nucleotides on the polynucleotide strand
4. They are then joined together by DNA polymerase

Good to visualise with a animation: http://www.youtube.com/watch?v=zdDkiRw1PdU