in this video, we're going to introduce the cell cycle checkpoints. And so recall from our last lesson video that these cell cycle checkpoints are very important for controlling or regulating the cell cycle to make sure that errors do not accumulate and to make sure that the cell does not prematurely enter the next phase of the cell cycle. And so these cell cycle checkpoints really act like stop signs where the cell can pretty much stop and make sure everything is okay before it moves on to the next phase. And so we're going to talk about four major checkpoints that control the progress of the cell cycle. And so if we take a look at our image down below notice, we're showing you the image of the cell cycle from our previous lesson videos. But notice here that we've included the four major checkpoints which pretty much act like stop signs throughout the cell cycle, where the cell will literally stop it each of these checkpoints to make sure that everything is okay before it proceeds into the next phase. And so notice that we have these four checkpoints here at each of these positions and so at each of these checkpoints, they're going to be very specific events that occur. And what's really important for you all to note is that the events of these checkpoints really don't need to be memorized. You don't need to memorize them if you understand the cell cycle itself. And so if you understand the events that occur at each phase of the cell cycle, then really you don't need to memorize these checkpoints because the checkpoints and the events that occurred, the checkpoints are going to be dictated by the events that occur in the cell cycle. And so the very first checkpoint that we're going to talk about is the G one checkpoint, which occurs right at the end of the G one phase of interphase. And so notice that here is the G one phase of interphase and right at the end of the G one phase of interphase, there is the G one checkpoint, which again is gonna act like a stop sign for the cell where the cell is going to stop to make sure that everything is okay before it proceeds. And so, at the G one checkpoint, what we need to realize is that, uh, the G one comes just before the S phase, and the S phase is where the DNA is going to get replicated or duplicated or synthesized. And so, before the DNA gets replicated or duplicated or synthesized, the cell needs to make sure that the DNA doesn't have any errors in it. And if the DNA does have errors in it, then the DNA needs to be fixed before the DNA gets replicated. Otherwise, the DNA, uh, the errors that air in the DNA are just going to get replicated, and that won't be something good. And so this G one checkpoint again, it's gonna be dictated by the events of the phases that come after. And so during the G one checkpoint again, which acts like a stop sign for the cell, the cell is going to stop and fix any damage or mutated DNA in preparation for DNA replication in the S phase. And so, of course, after the s phase, the DNA is going to get replicated and the centrism is also going to get replicated, and that leads us to our second checkpoint, which comes at the end of the S phase. The S checkpoint. And so if we go up here, we can see that the second checkpoint here is going to be the s checkpoint. And, of course, during the S checkpoint. What we need to realize is that the cell has just finished replicating or duplicating or synthesizing its DNA. And so what the cell wants to do is it actually wants to confirm the proper replication of the DNA to make sure that the DNA was replicated completely and fully and properly. And so Thea s checkpoint is going to confirm proper replication of the genetic material, and it's also going to attempt to fix any errors that may have occurred. And so that is what happens at the S checkpoint and then notice that the third checkpoint after that is the G to checkpoint, which comes at the end of the G two phase. And what we need to realize about this G to check point is that the G to checkpoint comes just before, uh, the M phase might Assis. And so at the G to checkpoint the sell pretty much wants to make sure that it has all of the enzymes and proteins that it needs in order for my toast is to proceed properly. And so that's exactly what is going to happen here at the G to checkpoint at the G to checkpoint the cell again is going to stop because the checkpoints kind of act like stop signs and the cell is going to stop and ensure that all of the enzymes and proteins that are needed for my toasts and psychokinesis are available. And if they're not available again, the cell is going to stop at this checkpoint to make sure that they are available. And then, of course, last but not least, we have our final checkpoint here, which is the M checkpoint, which comes right in the middle here at Meta phase. And so, of course, during meta phase, we know that all the chromosomes are supposed to line up in the middle, and that's exactly what the M checkpoint is checking for. So during the M checkpoint, which really is the meta phase checkpoint, the cell is going to stop and confirm that all of the chromosomes have actually aligned properly at the middle of the cell. And so it's going to check to confirm that all chromosomes are aligned in the spindle fibers are attached properly. And so again, if any of these checkpoints are not working properly, then that can lead to an unregulated cell cycle. And ultimately that can lead to the development of cancer. And so these checkpoints are very, very important to make sure that the cell cycle is under control and that it's regulated properly. So that cell division occurs on Lee when it's supposed to, and that cell division occurs properly. And so this year concludes our introduction to the four cell cycle checkpoints, and we'll be able to get some practice applying these concepts as we move forward in our course, so I'll see you all in our next video.