Definition:

DNA polymerases are essential enzymes responsible for replication and repair of DNA in all organisms. Based on sequence homology, DNA polymerases have distinct families, including A, B, X, and Y. To replicate DNA with high fidelity, DNA polymerases must select the correct incoming nucleotide substrate during each cycle of nucleotide incorporation, in accordance with the templating base. When an incorrect nucleotide is sometimes inserted, the polymerase uses a separate 3'→5' exonuclease to remove the misincorporated base (proofreading).