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In this video, I'm going to explain the stages of the cell cycle and mitosis. Now, I find that most students start with the stages and memorize facts about each stage, but then end up forgetting it all because they don't understand how those steps work together in order to help the cell divide. So, I'm going to teach you the story of mitosis in a way that you can understand, and then we'll go back and name the stages and practice so that by the end
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of this video, you'll have it all memorized. To help visualize this, we'll use a hyperrealistic 3D simulation from Anatomage's Science Table, an interactive digital platform with essential experiments across biology, chemistry, earth, and space science, and physics. So, quick, before any more of your cells divide without you understanding how they do it, let's jump to the whiteboard and get started. By the way, I have a free study guide that goes along with this video.
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It has a notes section that you can follow along with as well as a practice section so you can do some practice to really learn this stuff linked in the description and in the pin comment. So check that out if you think that would be helpful. All right, we're going to start with this diagram and we're going to use this as sort of a map that we're going to follow during the stages of the
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cell cycle mitosis. So first we have interphase. Interphase is everything that's happening whenever the cell is not dividing. And then we have mitosis which is the process of the cell actually dividing up into two different cells. And that process of interphase lasts a lot longer than that process of mitosis. Now interphase is split up into three parts. The first part is G1. That G stands for
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gap or growth. There's some things happening there but a lot of times we think about that as a stage where not a lot is happening. It's not completely true. There's there's a lot that is happening. After that G1 we have the S stage which stands for synthesis. because it's going to synthesize or copy its DNA. So, we'll have a second copy of the DNA. Then, we'll enter another Gphase, G2 or gap 2 or growth 2, and that's going to be where that cell is getting ready to divide. It's
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kind of the final steps before it divides during mitosis. And then we have mitosis, which is split into four parts. We have proase, metaphase, anaphase, and telophase. Some sources will have a phase called protaphase. We can organize this a little bit differently, but PMAT, prophase, metaphase, anaphase, telophase is the most common way that we kind of do that. Later on in the video, we're going to get into what happens in all of those, but right now, just know that
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mitosis is that process of cell division. At the end of that, we should split into two different cells. We call that process cytoinesis. Cyto means cell. Kinesis meaning movement. So, it's like these cells move apart and form two different cells. And then we're back where we started in G1. Now, at the end of G1, there's something called the restriction checkpoint. Basically, what the cell can do is it has a branching path at this point. It could continue on to the S
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stage. And once it continues on to the stage and it's copying its DNA, it's really committed to doing this whole process again and dividing into a new cell. But not every cell in the body wants to keep dividing. In fact, that would be really bad. That's kind of what cancer is, where cells divide uncontrollably and start to damage other tissues and stuff in the body. So, we have this
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restriction checkpoint. It can depend on a lot of different factors whether or not it continues onto the Sphase and advances onto mitosis or a couple other things can happen. One, we have this G0 phase. And the G0ero phase is when that cell will sort of, you know, skip this process and it's just going to go and carry out its cell functions. That cell might specialize. Maybe that's a brain cell
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or a liver cell or a pancreas cell or whatever cell in the body and it's just going to go do its cell function and do it well and not worry about dividing and dividing. We have other cells in the body. They're going to be dividing dividing all the time. But that's one option is it can go into that G0ero phase. Sometimes we call that the rest phase or specialization differentiation. It
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can also undergo apoptosis. And apoptosis is this process of cell death. And that can happen for a few different reasons. Maybe we don't need that cell anymore. Or maybe that cell sort of outlived its lifespan. Or maybe there's something wrong with that cell and the the body has found that there's mutations in that cell that can cause a lot of issues and it detects that and says we need to just kill this cell so it can't go on and reproduce and spread. So that restriction
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checkpoint happens at the end of G1. So that was a lot of information so far. We've got the phases of interphase. So gap one synthesis where it's copying the DNA gap two and then we've got the stages of mitosis prophase metaphase anaphase telophase. At the end of that it'll have split up into two different cells. That's kind of our map of this whole process and we're going to keep that map kind of in the corner of the screen for most of this so we can kind of see where we are. But
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now we're going to dive into the story of the cell cycle and mitosis and see exactly what's happening in each of those stages and why so we can understand this process really well. So let's start with the cell and we're going to start in that G1 phase. So we're right here in G1. The cell is going to divide eventually but it's not ready just yet. So let me map out a few things on our diagram here. First we have the centrosome. The centrosome is made of two centrialsles and
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they're organized at kind of 90°. So there's a centrial, [snorts] there's a centrial and together that complex of two centrialsles is called a centrosome. We're going to have several vocabulary terms that sound very similar. Centrial, centrosome, centromeir, chromosome, chromatid, chromatin. A lot of vocab going on in this, so I'm going to try to keep it really clear what's what. The main thing, if you remember at this point, is that this is a centrosome. It's the main thing
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right now. Here we have the nuclear envelope or the nuclear membrane. And so that's just the the membrane around the nucleus of the cell. So this whole thing in purple here is our nucleus. And that outer part is the nuclear membrane. These little gaps in between there is our pores because there's little gaps in there where things can move in and out of that nuclear membrane. And then we have our DNA which is in the form of chromatin right now. Now you may be used to saying that
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there are chromosomes in the nucleus of a cell but at this point it's in the form of chromatin. So instead of distinct chromosomes that are all you know those things that are shaped like an X instead of those being distinct it's all one kind of tangled ball of genetic material of DNA called chromatin. Later on we're going to condense that chromatin into chromosomes but we're not there just yet. So again we have our center zone. We've got our nuclear envelope around the nucleus and
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then we've got our DNA, our genetic material in the form of chromatin inside the nucleus. So let's check out what's going to happen in this G1 phase. So the first thing is that the cell is going to grow. So we have our cell growing there. Remember this cell has just undergone cell division. It has just undergone mitosis and we end up with these two smaller cells because the cell split. So now we need those cells to grow. So we have some cell growth. And then we're also going
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to copy a lot of the organels. So, you know, it's got half the organels that the parent cell had before it divided. And now we're going to copy a lot of those organels so that we have the right number of them. A lot of this interphase is going to be the cell like creating new stuff like new organels or genetic material and things inside the cell. So, it's going to copy a lot of the organels
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and that's the G1 phase. Next, we're going to move to the Sphase. Now, before we get to that Sphase, remember we have that restriction checkpoint where the cell is going to decide based on other factors in the environment and in the genetic material whether or not it's going to undergo cell division. It may go to that G0ero phase and differentiate or rest or just carry out its normal functions. It might undergo programmed cell death or aptosis or it may continue on to the Sphase
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of interphase. Now, a couple things are going to happen in the Sphase. One is the centrosomes are going to copy themselves. So now we've got a copy of those two centrosomes. The reason we need that, those are going to actually eventually migrate to the two sides of the cell and they're going to pull the DNA apart in order to make the sets of DNA that each cell after mitosis will have. So we're going to copy those and we're also going to replicate the DNA. So here's that process
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of replication. Now it's not represented perfectly on my diagram there. It doesn't necessarily happen exactly like that, but I'm limited in my animation skills here. So, we've replicated the DNA. So, we essentially have two copies of that genetic material in the nucleus now. That's why we call this the synthesis phase because we're replicating our DNA. We're synthesizing new DNA. So, we have
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got two copies of that DNA now. And now, we're going to move to the G2 phase. In the G2 phase, a few things are going to happen. One, the cell is going to look for and fix any errors in that genetic material. remember it just made a copy of it and it wants to make sure that that copy is an accurate copy without any mistakes in it and but you know this is all biological little reactions happening and so mistakes can happen so it's going to look for those mistakes and fix any
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and then it's going to keep building new proteins preparing for mitosis or the separation of these I'm not going to draw any of those proteins and stuff in there cell biology is way more complex than in any single like YouTube video that you're going to find at this length. Um, but just know that it's doing lots of other things like making proteins, preparing for that stage of mitosis. So,
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that's G2. Just to recap real quick, in G1, the cell was growing, copying a lot of organels. In the Sphase, we replicated the DNA or synthesized new DNA and the centrosomes duplicated. And then here in the G2 phase, we fixed the errors in the DNA and we've made proteins for mitosis. Now, we're going to move on to mitosis. But like I said in the intro, I don't want to go into each phase just yet. We're going to go through the whole process of mitosis. And then when we go back
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through the cell cycle again, we'll talk about which of those steps go in each of those phases. And this will be a better way to learn it because you're not going to be focused on memorizing the stages yet. You're going to focus on memorizing the whole process and why everything's happening. And then we can separate it into stages later on. So in mitosis, one of the first things that's going to happen is our chromatin, which is this kind of tangled um ball of DNA is going to
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condense into chromosomes. It's going to coil up tightly into these distinct chromosomes. So I have that being kind of shown on the diagram there. And now we have these X-shaped chromosomes. Now in in the human, we're going to have 23 pairs of these 23 of these X's. But I'm not going to draw 23 in here because it's just going to make the diagram um harder to animate. and look kind of wild. So,
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I've just got four in there, but remember we have 23 of these in the human body. And before we go to the rest of it, I want to jump to this animation um from anatomage, the simulation, and to kind of see what this process looks like in sort of three dimensions and all of that. So, I'm going to talk through this process and then we'll go back to our other diagram. So, here we have our cell and
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up here we have our centrome and we've got our nuclear envelope and of course the cell membrane itself around here. And so one of the first things that we're going to do is split those centrosomes. So that was back in the Sphase and those are going to start to move to opposite sides. Also happening right now is we're condensing that chromatin into chromosomes. We don't see that happening here because that's happening inside the nuclear envelope. So we can't see that through there,
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but that is happening. And then next our nuclear envelope is going to dissolve. And then those centrosomes are going to work their way to the opposite sides of the cell. Remember, our goal here is to take this DNA, these replicated chromosomes, and we're going to split them apart so that we can form this new cell. Now, we had the nuclear envelope in the way, so we had to dissolve that. We had the chromosomes as chromatin, so we had to condense them into chromosomes. And we had
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to copy our centromes and move those to opposite sides of the cell. And now, they're going to send out these little things called spindle fibers in the glowing green right there. And those are going to attach to the chromosomes. Now you see the chromosomes now moving toward this kind of midline of the cell and then the spindle fibers are going to attach to those and we're about to see those yank those apart here in just a moment. There we go. So it yanked those apart and we call
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each of those sister chromatids. So chromosomes get split into sister chromatids and we see we've got one set of those on either side of our cell now. And you can kind of start to see where we're going with this where now the cell is going to be elongating out like this. You see those chromatids kind of moving into a together in the center of the cell. The spindle fibers are releasing and
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now we've reformed a new nuclear membrane and the cells move apart. We now have two new cells. That last process there was the process of cytochinesis where the cells were actually moving apart from each other. So they're together here and then that's cytochinesis and we end up with two cells that are basically identical to the one cell that we started with. So that was pretty quick but that
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was the full process of mitosis. Now let's go back to our diagram that we were working with and break that down a little more. So here we are. We've got the chromatin which is condensed into chromosomes and next thing is the nuclear membrane is going to dissolve. Remember that membrane's in the way. For those spindle fibers to attach and pull the chromosomes apart, we got to get rid of
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that nuclear membrane. So, we're going to dissolve that nuclear membrane. And then from there, we're going to take those centrosomes and those are going to move to opposite ends of the cell. So, we see those moving to opposite ends. Now, my animation there was a little bit jerky, but that's just the limitations of my animations that I'm doing. Then, the chromosomes are going to line up. So, they're going to line up on the midline of the cell there, getting ready
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to be pulled apart. So we condense that chromatin into chromosomes. Dissolve the nuclear membrane centrosomes to opposite ends. And now we line up those chromosomes. Now we got to send those spindle fibers out so they can grab onto the chromosomes. So here those spindle fibers are going out. Now the middle of those chromosomes, the middle of the X's where they come together like this, those are called centro mirrors. Centro for center, mirror meaning for like measurement.
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So it's like if you were to measure the center of these X's, those would be the centromeirs. So don't get all this confused. We've got centrosomes right here. This is the centromeir of the whole chromosome. And then those spindle fibers attach and then next they're going to pull those apart into sister chromatids. So we've got chromosomes right now. Those are going to get pulled apart.
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Now each of these is a pair of sister chromatids. sisters because they're s sort of identical copies of that uh of that genetic material and they're going to get pulled apart. You see those pulling apart and the cell kind of elongating right there getting wider and then those are going to come together in kind of one spot. all those chromatids in one spot. And then we're going to reform that nuclear envelope because remember our goal is to split the DNA, split the chromosomes,
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and then reform a new cell that's just like that parent cell. So we're going to reform that nuclear envelope. We see that happening here. And then after that, we've just got one thing left or two things left, which is our chromosomes have to decondense back into chromatin. So they're going to reform back into chromatin like we had originally. And then it's time to divide those cells. This is the process called cytoinesis or the cell splits into [snorts] two. So we're going
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to have this split like this. This is called the cleavage furrow right there and right there. And then it's going to continue separating like this until we have two distinct cells we have right there. So now we've got two daughter cells that are almost identical copies to that parent cell that we started with. All right. So, we've gone through this whole process of the cell cycle and mitosis at this point. Now, we're going to go back through it a little bit quicker this time.
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And this time, we're going to separate out those stages of mitosis, prophase, metaphase, anaphase, and telophase. So, we're back here in this G1 phase. We're going to bring our map back out so we can see that. Remember, in the G1 phase, we're going to have cell growth, and then that cell is also copying a lot of its organels. Then, we have that restriction checkpoint. If we decide to go on
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to the rest of interphase, we have the synthesis phase and again that's when the centroomes are going to copy. So we have two centrosomes and then our DNA is going to replicate. So we're going to have our second copy of that DNA and then from there we'll go to that G2 phase. Remember in the G2 phase we're going to fix the errors in DNA and then we're going to make proteins for mitosis. Basically preparing for mitosis. And then we're into the stages of mitosis. And we're going to
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start here with prophase. Now remember our goal here. Our goal here is to separate this DNA into two different parts and split the cell so we can form a new cell. So that's our goal. Keep that in mind because that'll help you remember all the steps that have to happen for that process. Now, as we're navigating these four stages, one way that I think about it is metaphase is really easy
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to identify. Meta means middle and that's when all the chromosomes are lined up in the middle of the cell. Anaphase is when they're pulled apart. So that's easy to see too because the spindle fibers are pulling them apart. Those are the two easiest stages to identify. Prophase is everything that happens up to that point where the chromosomes are lined up in the center. And then telophase
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is everything that happens after they get pulled apart. Not only that, but prophase and telophase are kind of the opposites of each other. So in prophase, we're going to condense the chromatin into chromosomes, but then in telophase, we're going to take those chromosomes and decondense them back into chromatin. Or for example, in prophase, we're going to dissolve the nuclear envelope. But in telophase, we're going to reform that nuclear envelope. So keep that in mind.
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Proase and telophase are kind of opposites of each other. And then metaphase is where the chromosomes are lined up in the middle. And anaphase is when they're pulled apart. So now let's go through this process and see all of those phases in action. So prophase, we're going to start with this. Our chromatin is going to condense into chromosomes. And then from there, the next step is that the
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nuclear membrane is going to dissolve. So we'll dissolve that nuclear membrane. We're getting this all set up in order to be divided. And then our centrosomes are going to move to opposite ends of the cell. Basically, it's done everything it needs to to get ready before those chromosomes line up in metaphase. So those are the three things that happen in prophase. Chromatin condenses into chromosomes. Nuclear membrane dissolves. Centrosomes move to opposite ends. Next we
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have metaphase. Easy to identify. Metaphase is where all of those chromosomes are going to line up in the center of the cell like that. And then the spindle fibers are going to attach to the centromeirs of the chromosomes. So we'll attach those spindle fibers and those are the two things that happen in metaphase. Chromosomes lined up and then the spindle fibers attached to the chromosomes. And just remember meta means middle. Next we have anaphase. Anaphase is when
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they get pulled apart. So the chromosomes are going to pull apart into sister chromatids. We pull those apart like this. And that is the process of anaphase. Anytime you see the spindle fibers pulling those chromosomes apart, that's going to be in anaphase. And then telophase, we're going to basically undo all the stuff that we did in prophase. So let's go on to telophase. First thing we're going to do is reform that nuclear envelope. So we have that nuclear envelope
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reforming. And then we're going to take those chromosomes and form those back into chromatin. So chromosomes formed into chromatin right here. And during this whole stage of telophase, the cell has started to elongate and start to split into two. And we call that cell division stage cytoinesis. Now sometimes you'll see cytoinesis as its own kind of stage of mitosis. There's different ways
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that we organize this. In this video I'm treating prophase, metaphase, anaphase, telophase as the four stages and cytoinesis as its own kind of thing that's happening as well. But depending on the source you look at, they might organize that slightly different. So we end up with two distinct cells like this. And that is the process of mitosis. And then from there, we go back to the G1 phase and we start this whole process over again. Let's go to our simulation from anatomage
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one more time. And then I'll show you a slide that'll have all of this kind of displayed in one spot so you can use that to review. So here we have our cell and we've got our centrosomes which just split. We're now in prophase and so our nuclear envelope is going to dissolve. Our chromatin has condensed into chromosomes and our centrosomes are going to move to opposite sides of the cell. Now we're moving into metaphase where the chromosomes are going to line up and the
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spindle fibers are going to reach out and grab the centromeirs of the chromosomes. Then we're about to move into anaphase where the spindle fibers are going to pull the chromosomes apart. So here's anaphase. And then after anaphase, which is pretty quick, we're going to move into telophase. In telophase, the cell is going to be elongating and we're going to reform that nuclear envelope right in here. Just a moment. There's a nuclear envelope. We got cytochinesis. And then
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the chromosomes are going to decondense back into chromatin. So that's the process of mitosis. Now, here's that slide I talked about where I have all of the four stages of mitosis kind of laid out in one diagram. This will be helpful if you're taking tests on this and stuff and you need to be able to kind of, you know, identify based on a diagram which phase you're in. I recommend pausing the video and seeing if you can explain all of the stages of mitosis without the descriptions
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of things happening um in these four stages. And then here's that information back so you can kind of check and see how you did. Now remember, if you need more practice on this, I have that free study guide with the notes as well as the practice activities. It's linked in the description and the pin comment. So check that out if that would be helpful. Again, thank you to supporters of the channel and thank you to Anatomage for sponsoring this video.
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Anatomage makes not only the science table but also the anatomage table which has cadaavveric models which are taken from actual cadaavvers actual human bodies and recreated in such a way that you can peel back all the layers and see the actual anatomy of people that were alive not just like an idealized version of it. So it's a really cool really cool thing and thank you to Natimage
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for sponsoring this video. You can find out more about them in the link in the description as well. And if you're ready to go on to another video and keep learning anatomy physiology with me, here's another video that might be helpful for you. So, click that if you want to keep on learning. Thanks for being here. Hopefully, this was helpful and I'll see you in the next video. All right. Bye.
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