Overview of the Cell Cycle - Online Tutor, Practice Problems & Exam Prep

Cell Cycle Overview

Hi. In this video, we're going to be doing an overview of the sales cycle. So, first, there are 3 classes of cells, and that's based on how frequently they, or whether or not they divide at all. So there are cells that don't divide at all, so those are going to be things like nerve cells. There are cells that normally don't divide, 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 going to focus on, is divided into 4 phases. Now, I'm sure you got over this in your intro bio class. We're going to 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 2 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 M phase, which is cell division. This includes things like cytokinesis, which is the process of actually physically separating the 2 cells that have divided. So, here's the stages of the cell cycle. Usually, they're generally drawn in a circle because they do repeat often. So, you have interphase which isn't really listed here, but you have this growth phase followed by replication, and the S phase, followed by another growth phase, and then a really short, but super important phase, which is where the cell is actually dividing. So the cell cycle, super important. I mean, obviously, if they mess it up, it's 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, there are going to be breaks in the cell cycle, where the cell just takes a minute, takes a pause, and actually looks and makes sure that it's done everything correctly before it moves on to the next stage. And so, this is super important because if these checkpoints 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 important. But it occurs at different rates because cell division occurs at different rates depending on the cell type. So this is actually measured through what's known as the mitotic 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 know, you have a million cells and one of them is in mitosis, it 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. Rapidly. So this is a measurement that does that, but the fact that they occur at different times and different rates, is kind of unique because cell division is actually extremely similar between multiple cell types. 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 checkpoint. So you've seen this before just a couple of seconds ago of all the different phases. 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 G1 checkpoint 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 to make sure that it's occurred right. You have this spindle assembly checkpoint, making sure that the cell is going to be able to divide itself correctly, making sure all the microtubules are in their right places. 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.

Which of the following is not a phase of cell division?

• A. GAP Phase
• B. M Phase
• C. S Phase
• D. L Phase

All cells undergo cell division at the same rate.

• A. True
• B. False