All right. So DNA is constantly repairing de uh the ep the replication process as it's happening. Um a lot of the same enzymes that we've been talking about are involved in this. So what happens is there will be times when the DNA molecule is damaged and that damage can happen from UV light uh and form thymine DR. Thymine DRS form when the UV light causes two neighboring thymine bases on the same DNA strand to bind together rather than across from each other. So if you look at this picture here, this is showing you a thymine dimer. That's not how it should look, right? So there needs to be a repair because now this DNA has a kink or distortion and it's going to block replication and transcription which we'll talk about um in another topic. So we have to fix this. So there's enzymes that come in and they cut out the damaged region um out of the bubble and they will add in the new DNA to repair and fill in the gap that was left. So what cuts the DNA is called a nucleas and nucleases are enzymes that break down nucleotides. DNA pulymerase is going to fill in the gap with the correct nucleotides and then DNA liase seals the repaired section to the rest of the strand and it restores this the DNA strand back to its original um structure. DNA pulymerase 3 which we talked about is the main pymerase that adds nucleotides is actually a proofreading enzyme as well on the new DNA and that's what's going to allow the use of those exonucleases um to function by removing and replacing the wrong bases. So it DNA pulase 3 can act as an exonucleus but we also have exonucleases that function separately from DNA plyase 3. Obviously, DNA plyase 3 is a more convenient enzyme to use because we're already using it to build the new strand. So, why not use it to also repair the strand?