The enzyme DNA polymerase III is the primary enzyme involved with bacterial DNA replication. It performs the 5'-3' polymerase function, which means that it adds nucleotides to the 3' end of the forming DNA strand during replication.
Before replication can start, the enzyme helicase unwinds the two DNA strands. Both strands become templates for replication. DNA polymerase III cannot add free nucleotides to these strands until primers have been added by the enzyme primase. There is also a DNA polymerase I that proofreads the newly synthesized DNA strands to make sure the appropriate nucleotides were added. It fixes mistakes when they are found by removing the bad nucleotide and adding the correct one.