Overview of the Cell Cycle

Hi in this video, we're gonna be doing an overview of the sales cycle. So first there are three classes of cells and that's based on how frequently they or whether or not they divide at all. Um So there are cells that don't divide at all. So those are gonna be things like nerve cells, there are cells that normally don't do but they can if they need to. So those are going to be mainly liver cells as an example of that. And then the majority of all the other cells divide often. So stem cells, white blood cells, skin cells, all these other types of cells really the rest of them for the most part. And so the eukaryotic cell division, which is what we're gonna focus on, is divided into four phases. Now I'm sure you've got over this in your intro bio class. We're gonna get really detailed in all of these phases, but for now let's just quickly review them. You have interphase, this is the period between cell division. You have gap phases. Now this is plural, there's actually two of them but both of them are growth phases and they proceed and follow DNA replication. You have the S phase which is where DNA is replicated and then you have em phase which is cell division. This includes things like psychokinesis, which is the process of actually physically separating the two cells that have divided. So here's the stages of the cell cycle. Usually they're generally drawing a circle because they do repeat often. So you have interface which isn't really listed here, but you have this growth phase followed by replication in the s phase, followed by another gross phase and then a really short but super important what we're mainly gonna focus on um uh in phase, which is where the cell is actually dividing. So cell cycle super important. I mean obviously if they mess it up, you're not going to divide, you can't grow, you can't reproduce, you can't do anything as an organism. So cell cycle control and regulating this. Super important to ensure that the cell division is accurate. So there is this system called the cell cycle control system and it's a network of different proteins that control cell division. So the cell cycle control system is broken up into checkpoints and these are exactly what they sound like, right. So they're going to be breaks in the cell cycle when the cell just takes a minute, takes a pause and actually looks and make sure that it's done everything correctly before it moves on to the next stage. And so this is super, super, super important. Because if these checkpoints or are missed or the cell cycle control system is messed up, then who knows what you're going to get. You can get cancer, you can get death, you can get lots of really bad things that no one wants. So this is super, super important. Um but it occurs at different rights because cell division occurs at different rates depending on the cell type. So this is actually measured through what's known as the mid topic index and this measures the percentage of cells in mitosis at a given time and so that gives you an idea of how often. So if you have a million cells and one of them is in mitosis probably doesn't divide very often, but you have a million cells and 900,000 of them are in mitosis, that's going to be a population that is dividing rapidly. So this is a measurement that does that um but the fact that they occur at different times in different rates um is kind of unique because cell division is actually extremely similar between multiple cell types. Um So even though they happen, you know, some happen slow, some happen really fast, they're doing the same processes. It's just occurring at different times. So, here are examples of cell cycle checkpoints. So you've seen this before, just a couple of seconds ago of all the different phase, you have your growth phases, you have your DNA replication and you have your division phase. But you can see here that I've listed a couple of checkpoints and these are real checkpoints. We'll talk about them more in future videos, but these are the real checkpoints. So you have this G one check point and make sure, you know, it's grown right, You have a G2 checkpoint, which makes sure it grows right and also checks a little bit for the DNA replication and make sure that is curved right. Um You have this like spindle assembly checkpoint, making sure that the cell is going to be able to divide itself correctly, making sure all the those micro tubules are in their right places. Um So all of these checkpoints super important for ensuring that the cell is undergoing replication appropriately, so that's the overview of cell division. So now let's move on.