Overview of the Cell Cycle: Study with Video Lessons, Practice Problems & Examples

The cell cycle consists of distinct phases: interphase, G1, S, G2, and M phase. Interphase includes growth and DNA replication, while M phase involves mitosis and cytokinesis. Checkpoints, such as G1 and G2, ensure proper cell division, preventing issues like cancer. The mitotic index measures the percentage of cells in mitosis, indicating division rates. Understanding these processes is crucial for grasping cellular growth and reproduction, highlighting the importance of the cell cycle control system in maintaining organismal health.

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

Here’s what students ask on this topic:

What are the main phases of the cell cycle?

The cell cycle consists of several distinct phases: interphase, G1, S, G2, and M phase. Interphase is the period between cell divisions and includes the G1 phase (first growth phase), S phase (DNA synthesis), and G2 phase (second growth phase). The M phase encompasses mitosis, where the cell's chromosomes are divided, and cytokinesis, where the cell itself splits into two daughter cells. Each phase is crucial for proper cell division and growth.

What is the role of checkpoints in the cell cycle?

Checkpoints in the cell cycle are critical control mechanisms that ensure the accuracy of cell division. Key checkpoints include the G1 checkpoint, which verifies cell growth, the G2 checkpoint, which checks for proper DNA replication and growth, and the spindle assembly checkpoint, which ensures correct chromosome separation. These checkpoints prevent errors that could lead to issues like cancer or cell death by pausing the cycle to correct any problems before proceeding.

What is the mitotic index and why is it important?

The mitotic index is a measure of the percentage of cells in a population that are undergoing mitosis at a given time. It is important because it provides insight into the rate of cell division within a tissue. A high mitotic index indicates rapid cell division, which can be normal in tissues like skin or bone marrow but may also signal abnormal growth, such as in cancer. Understanding the mitotic index helps in assessing cell proliferation and diagnosing diseases.

How do different cell types vary in their division rates?

Different cell types vary significantly in their division rates. Some cells, like nerve cells, do not divide at all after maturation. Others, such as liver cells, typically do not divide but can do so if needed. Most other cells, including stem cells, white blood cells, and skin cells, divide frequently. These variations are due to the specific functions and requirements of each cell type within the organism. The mitotic index helps measure these rates, providing a snapshot of cell division activity.

What happens during the S phase of the cell cycle?

During the S phase of the cell cycle, DNA replication occurs. This phase is crucial as it ensures that each daughter cell will receive an identical set of chromosomes. The cell synthesizes a complete copy of its DNA, resulting in two sister chromatids for each chromosome. Proper DNA replication is essential for maintaining genetic stability and preventing mutations that could lead to diseases such as cancer.