1. Three theories were suggested: Conservative replication a
DNA Replication
Three theories were suggested:
Conservative replication a
Dispersive replication
produce two DNA molecules with sections of both old and new DNA interspersed along each strand.
Semi-conservative replication
produce molecules with both old and new DNA - each molecule would be composed of one old strand and one new one.

3. DNA Replication is semi-conservative
Experimental Proof
(1957) Mathew Meselson and Franklin Stahl grew the bacterium Escherichia coli on medium that contained 15N in the form of ammonium chloride
The 15N became incorporated into DNA (nitrogenous bases).
The resulting heavy nitrogen-containing DNA molecules were extracted from some of the cells.

4. When subject to density gradient centrifugation, they accumulated in the high-density region of the gradient.
The rest of the bacteria were transferred to a new growth medium in which ammonium chloride contained the naturally abundant, lighter 14N isotope.

7. The newly synthesized strands were expected to be less dense since they incorporated bases containing the lighter 14N isotope.
The DNA from cells isolated after one generation had an intermediate density, indicating that they contained half as many 15N isotope as the parent DNA.
This finding supported the semi-conservative model - each double helix would contain one previously synthesized strand and a newly synthesized strand.

8. The nucleotides lining up by complementary base pairing are deoxynucleoside triphosphates
As the phosphodiester bond forms between the 5' phosphate group of the new nucleotide and the 3' OH of the last nucleotide in the DNA strand, two of the phosphates are removed providing energy for bonding

11. DNA polymerase enzymes are only able to join the phosphate group at the 5' carbon of a new nucleotide to the hydroxyl (OH) group of the 3' carbon of a nucleotide already in the chain.
As a result, DNA can only be synthesized in a 5' to 3' direction while copying a parent strand running in a 3' to 5' direction

13. Bacteria have 5 known DNA polymerases: Pol I:
DNA repair
has 5'→3' (Polymerase) activity
both 3' → 5' (proof reading) and 5' → 3' exonuclease activity (in removing RNA primers).
Pol II:
involved in repair of damaged DNA
has 3' → 5' exonuclease activity
Proof that this is not the main polymerase
Pol III:
the main polymerase in bacteria (elongates in DNA replication)
has 3' → 5' exonuclease proofreading ability.
is the principal replicative enzyme
is highly processive
2. catalyses polymerization at a high rate.