Key points: Cells have a variety of mechanisms to prevent mutations, or permanent changes in DNA sequence. During DNA synthesis, most DNA polymerases "check their work," fixing the majority of mispaired bases in a process called proofreading. Immediately after DNA synthesis, any remaining mispaired bases can be detected and replaced in a process called mismatch repair. If DNA gets damaged, it can be repaired by various mechanisms, including chemical reversal, excision repair, and double-stranded break repair.

Proof Reading: while printing a page, the typesetter set the types and impression is taken, proof reading is done to correct mistakes if any, and the final printing is done. A similar follow up mechanism is done after DNA synthesis. If DNA polymerase detects an incorrect nucleotide pair, it will remove and replace with the correct nucleotide immediately.

Mismatch Repair:even after DNA synthesis, mismatch area(insertion or deletion) can be identified on the newly synthesized DNA.

In the mismatch repair, specific proteins scan the newly synthesized DNA strand. The mismatch area is identified and loop.

The second protein complex remove the mismatch segment. Finally correct segment is synthesized by the help of DNA polymerase, SSBs and ligase.

DNA damage repair mechanism: when DNA get damaged, there's a repair process that fix the damage. This includes Direct reversal, excision repair and Double stranded break repair