Okay. So now let's talk about an unusual type of DNA repair called Translesion Synthesis. Translesion Synthesis is a really poor DNA repair pathway, and it's usually only used as a last resort. So, there's nothing else the cell can do, but it wants to prevent death, so it's going to use this pathway. What it does is typically repair types of DNA damage that cause the DNA polymerase to stall while it's replicating. And so, if it can't continue replicating, then the DNA is severely damaged, it can't replicate, it can't divide, and that usually triggers the cell to kill itself. Now the cell doesn't want to kill itself, so if there's any way that it can keep this DNA polymerase going and keep replicating, it wants to use it, and so it uses the Translesion Synthesis Pathway.
What happens is if there's some kind of distortion or mutation that causes the DNA polymerase to stall, then it sends in these extra polymerases called translusional or bypass polymerases, and they are recruited to the area. Translesion polymerases actually have the ability to overcome various helical distortions that cause the other polymerase to stall. They can move, but we lose some efficiency with that because they have no proofreading, so they can't fix anything that's wrong, they have a very high error rate, and they only do a few nucleotides at a time before they fall off.
Generally what happens is the replicating polymerase stalls because there's some kind of DNA damage here in red. The translesion polymerase will come in and it will overcome this DNA damage, but then it falls off because it's not very good at what it does, and therefore the replicating polymerase is added back on and it keeps going. Generally, that's how it works. And so it's good enough to overcome this distortion, but what it doesn't do is it doesn't fix the damage. Right? That DNA damage is still there, and now it's being passed on to another cellular generation, and it has a higher error rate and can cause mutations in addition to the one that's already existing that isn't repaired because there's no proofreading. Like I said, it's really poor, but it keeps the cell from death. And that is what's important for the cell at this point because it doesn't want to die but needs to replicate itself. And so, Translesion Synthesis is what allows the cell to prevent itself from dying in the instance of mutations. So with that, let's now move on.