DNA Synthesis DNA Polymerases Enzymes that replicate DNA using a DNA template are called DNA polymerases. Polymerization occurs only 5' to 3' 2.
Polymerization requires a pre-existing primer from which to extend.
I from E. coli was the first DNA polymerase characterized. There are approximately 400 molecules of the enzyme per cell. Like all known DNA polymerases, DNA polymerase I requires a primer from which to initiate replication and polymerizes deoxyribonucleotides into DNA in the 5' to 3' direction using the complementary strand as a template. Newly synthesized DNA is covalently attached to the primer, but only hydrogen-bonded to the template. Interestingly, polA mutants are defective in repairing DNA damage.