1. Two genetically identical copies of DNA
2. Finds an error in DNA, removes the incorrect nucleotide and replaces it with a correct one.
3. It is used as a copy/ "template" for replication in order to have two identical copies of DNA.
4. DNA helicase unwinds DNA double helix and Topiosomerase ensure there isn't too much unwinding.
5. Replication has a built on proofreading system - DNA polymerase removes the incorrect nucleotide and replaces it with a correct one.