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Current time:0:00Total duration:3:55

Speed and precision of DNA replication

IST‑1 (EU)
IST‑1.M (LO)
IST‑1.M.1 (EK)

Video transcript

in the earlier video on DNA replication we go into some detail about leading strands and lagging strands and all of the different actors all of these different enzymatic actors but I left out what is probably the most mind-boggling aspect of all of this and that's the speed and the precision with which this is actually happening as we talked about in that video it feels pretty complex you have this topoisomerase that's that's unwinding things the helicase is unzipping it then you have the polymerase it can only go from the 5 prime to 3 prime direction and needs a little primer to get started but then it starts adding the it starts adding the nucleotides on the lagging strand you have to have the art you get the RNA primer but then it's going in it's going from once again from 5 prime to 3 prime so you have these Okazaki fragments and all of this craziness that's happening and remember these things don't have brains these aren't computers they don't know exactly where to go it's all because of the chemistry they're all bumping with the into each other and reacting in just the right way to make this incredible thing happen now what I'm about to tell you is really going to boggle your mind because this is happening incredibly fast DNA polymerase has been clocked at least in e.coli has a clocked at approaching 1,000 base pairs per second I think the number that I saw was 700 something base pairs per second so polymerase let me write this down this is worth writing down because it's mind-boggling it gives you a sense of just how amazing what you do the machinery in your cells are so it's been as high as and it can change it can speed up and slow down and that's actually been observed but polymerase as fast as as fast as 700 plus base pairs per per second so if this on this diagram and it's just zipping it's just zipping along at least from our perceptual frame of reference so the second seems like a very short amount of time to us but at a molecular scale these things are just bouncing around and just getting this stuff done now the second thing that you might be wondering okay this is happening fast but surely there it has lot of errors well the first thing you might say well if I had a lot of errors that would really not be good for biology because you always have you have DNA replicating and all throughout our lives and at some point you just have so many errors that the cells wouldn't function anymore and so lucky for us that this is actually a fairly precise process even in the first pass of the polymerase you have one mistake you have one mistake let me write this down because it's amazing one mistake for every for every approximately ten to the seventh so this is ten million ten million in nucleotides nucleotides and that might seem pretty accurate but you got it we gotta remember we have we have billions of nucleotides in our DNA so this would still introduce a lot of errors but then there is proofreading that goes back and make sure that those errors aren't don't stick around and so once all the proofreading takes place it actually becomes one mistake one mistake for every approximately 10 to the ninth nucleotides so approximately you can you can do this in an incredibly fast pace as fast as 700 plus approaching 1,000 base pairs per second and you have one error every billion nucleotides especially after you go through these proofreading steps and so it's incredibly fast and it's incredibly precise so hopefully that gives you a better appreciation for just the magic that's literally I mean look at your hand or just think about this is happening in in all of the cells or most of the cells of your body as we speak