Each primer is eventually removed and replaced with deoxynucleotides. Each short segment is linked to adjacent segments by DNA ligase. When the DNA molecule is completely replicated, the enzymes leave the molecules, and other special enzymes help the completed molecules return to their helical shapes. When DNA is being replicated, errors are made in the placement of nucleotides at a rate of about 1 error per 10,000 base pairs. Repair processes reduce the eventual error rate to about 1 per 1 billion base pairs.
Mismatch repair is the process for fixing mistakes during replication.
DNA polymerase has the capacity to notice improperly paired nucleotides, remove the incorrectly placed ones, and fasten in the correct ones after they are in place. DNA may also be damaged by chemicals and various kinds of radiation, including ultraviolet radiation. Damaged sections of DNA can be removed by nucleases. These are often damages that occur in one of the strands of the molecule. DNA polymerase and DNA ligase can fasten in the correct nucleotides.