Definition: Polymerase is a chemical reaction catalyzed by enzymes in bacteria that converts phosphoribosylpyrophosphate to pyrophosphate, an active base for DNA replication. Detailed definition: Polymerase is a DNA polymerase enzyme, a type of enzyme that catalyzes the addition of a nucleotide deoxyribose sugar at each nucleotide of a DNA strand and forms pyrophosphate (a byproduct) from phosphoribosylpyrophosphate (a precursor).