Mitosis

Hello everyone in this lesson. We're going to be talking about how a cell enters into the process of mitosis and how the chromosomes are going to be condensed and ready for the process of separation. Okay so we know that mitosis is cellular division and we know that that cellular division requires the chromosomes to be separated from one another and then divided into two daughter cells. But remember that chroma you have to be really really condensed to do this process. But first let's talk about how a cell actually gets into this phase. Because we've talked about the cell cycle right? And the cell cycle are going to be the stages and steps that a cell takes before it goes into cellular division. So the cell has to go through G. One S. And G. Two phase before entering into in phase or mitosis. Remember G one phase is basically the first growth phase where it's getting ready and preparing its size and its nutrients and its growth hormones. And then S. Phase is going to be the synthesis of D. N. A. Phase or DNA replication phase Where the cell is making enough DNA to turn into two cells. And then G. Two phase is basically just the preparatory phase for in phase which then and follows. So how does the cell actually go into this process into the M phase of mitosis? What's going to utilize those M. Cyclones and cD case that we talked about in earlier lessons? Remember M. Cyclones or mitosis? Cyclones are going to be proteins that are going to increase in concentration before and during mitosis. And these Cyclones are going to bind to and activate independent penises or C. D. K. S. And M. Cyclones are going to tell the cd case to activate proteins that are needed for mitosis. So they are going to be responsible for the cell entering into mitosis. Now these M. C. D. K. S. Or the cycle independent penises that will bind to the M. Cyclones are going to be activated by the C. D. C. 25. C. D. C. 25 is going to be a protein specifically is going to be a phosphate based protein that is going to remove inhibitory phosphate groups from the cd case active site so that the C. D. K. Can actively bind to the cycling. Now, if you're wondering what CDC actually stands for, C. D. C. Is going to stand for cell division cycle protein. So it is the cell division cycle protein number 25 it is going to be a phosphate tastes which are proteins that remove phosphate groups, kindnesses add phosphate groups, phosphate cases, remove phosphate groups and it is going to remove a phosphate group from the active site of the C. D. K. Allowing the C. D. K. To bind to the cycling. Now, M. C. D. K. S instigate the process of chromosome condensation chromosomal condensate is incredibly needed and important for mitosis and mitosis because these chromosomes need to be separated and they need to be moved around the cell So they have to be compact and packaged nicely so it's just not a big mess of D. N. A. That's being dragged around the cell. So M C. D. K. S are going to begin the process of condensation by activating proteins that are needed for this process. So condensation is required for mitosis or those chromosomes just won't be untangled and they won't be able to move. Now the different proteins that are needed for this condensation process that are going to be activated are going to be the condensed sins. Their name is pretty self explanatory and the co he sins. So the condensed sins are going to be protein complexes that assist in chromosome condensation and segregation basically think of condensing xas condensing the chromosome. They're going to actually take that chroma tin and pack it really, really tightly together. And co he sins are going to be protein complexes that hold to sister chroma tides together and regulate their separation during an A phase. Remember sister chromatic kids are going to be identical copies of the replicated chromosome. Whenever the cell goes through s phase, the DNA is replicated it is copied and there are going to be two copies of each chromosome and those are going to be called sister chroma tides. They are going to be attached to one another via a specialized amount of D. N. A. Called the central meter. And the sister chroma kids are going to be also held together by these protein complexes called kohi sins. Now, if you think about this, what does the word cohesion mean? It means to stick together right cohesive? Our play off that word. So their job is to make the sister chroma kids cohesive or stick together. So cohesive. Make the sister chroma tides cohesive cohesive. If I can speak so now let's go down and let's actually look at what this looks like in a image. Okay, so um let's start with this one right here. So this big guy right here is going to be a chromosome. But this thing is atlantic, right? It's huge and it's going to have to shrink down if we want that thing to be able to be a condensed chromosome that is easily movable. So look at this, this is a chromosome and I want you to realize that this is a sister chromatic here in black and this is a sister chromatic here in black. And they are going to be attached via the centrum here which I will highlight in blue. Now the center mirror is going to attach them together. But so is the cohesive. And the cohesive is actually going to be these little green dots that you can see. So these green thoughts here are going to be the cohesive protein complexes that actively keep the sister chroma tides together. This is very very important and they will stay here until anna phase happens. And those sister chromosomes are pulled apart. And cohesive is really important for maintaining this structure. And it's really important because if the sitter chroma tides aren't held together really tightly in a really nice and regulated way, those sister chromosomes won't be separated correctly and they may not go into the correct daughter cells which can create a big problem. And then the genetics of the daughter cells will be all messed up. So cohesive. Very very important. Excuse me. Okay, so now let's go on to the next image right here. What happened? This is the same chromosome but it's shrinking. It's getting shorter and shorter and shorter. And that is because of the condensing and the condensing are going to be these red protein complexes here and they are going to be these big protein complexes that basically grab onto the D. N. A. And start twisting and turning it and making it really really compact. And then you can see the next step, it's even shorter and you can see that this is a really fully condensed chromosome. It's really small. It's a lot more removable than the one over there. Right? It's really easy to grab and move and transition into the daughter cells. This is going to be called a meta phase chromosome because during meta phase the chromosomes are extremely compacted and they are ready for movement in the next stage called the ana phase. So the co heat condense sins. Sorry. The condenser will stay on these chromosomes until the sister chromosomes have been separated and then transported into the daughter cells and the daughter cells nuclear envelope has reformed. Then the condense sense will leave the chromosomes and allow them to begin to un condense or get much looser inside of their new nuclei. But condensing and cohesion are very, very important for the compaction and the connection of the sister cremated so that they are ready for transport during the process of mitosis and mitosis. Okay, everyone, let's go on to our next topic.

Okay, so now let's go over the individual steps of mitosis. Now I know you went over this in air intro bio classes but hopefully I'll be giving a little bit extra information and maybe even an extra step for some of you. So the first step is pro phase and the important thing to know about pro phases. This is when the main topic spindle forms. So you may say, okay well what's the topic spindle? I don't remember. Well the main topic spindle is a network of micro tubules called disaster micro tubules sometimes and central zones that control mitosis. And so my topic spindle has two spindle poles where micro tubules are attached to the central zones on two central zones. Now if you remember what central zones are there those like they're always drawn like this essentially. Um But they're made up of micro tubules as well. And those micro tubules come out of the central zones and there's two of them at each end of the cell. And those micro tubules stick out. And so the methodic spindle actually forms because there are central zone duplication occurring during S. Phase. When the D. N. A. Is duplicated. And so each one of these central zones then moves to opposite poles of the cell. Um And so this is what happens during pro phase where the main topic spindle is forming and moving to the other side of the cell. Then you have a potentially new step for some of you. Some of you may have gone over this but it's pro meta phase and this is the step where the nuclear envelope is disassembled. So remember the nuclear envelope surrounds the nucleus and it breaks down during pro meta phase. So when it breaks down that exposes the chromosomes, right? So there's micro tubules that are coming from the mid topic spindle begin to attach to the chromosomes at a specific location called the kinetic Or And so because there are two poles and each of those micro tubules are coming in at different ways. Um each one of the poles attaches to each one of the sister chroma tides. So we say that is like being by um having a bi orientation. So each sister committed is attached to the opposite poles. So here we have an example of what this looks like. We have pro face. You can see an interface just here. You have chrome a tin and chromosomes but you can't really see the chromosomes right there. Just kind of it just looks like spaghetti almost because it's not condensed yet. So in pro phase you start seeing these actual chromosomes and this is because they're condensing and that makes them visible. You also see the main topic spindle. So here's one and here's one with those micro tubules that kind of look like spider legs extending out from them. So that also happens during pro face. Then you have pro meta face. And this is where the nuclear envelope which was keeping the keeping the micro tubules from the my topic spindle and the chromosomes separate breaks down. So now the micro tubules begin to interact with the chromosomes and each sister chrome a tide of a chromosome. So each one of these travels is attached to an opposite spindle, that's what that looks like. So one is going to be attracted over here and the other one's gonna be attracted over here. So then we get to meta phase. So meta phases when the duplicated chromosomes align at the spindle equator. So this forms a meta face plate which is just a line of chromosomes straight along the equator. So it forms this line essentially in the middle of the cell. And so there's a really important checkpoint here called the spindle assembly checkpoint. And this checkpoint stops the cell cycle and make sure that the chromosomes are aligned properly so they're straight in the middle. And if they're not then it delays entry into um anna phase because they aren't aligned properly. It must be a space there. So after that they're now aligned in the middle. So now we can move on to anna phase. And this is where the cohesion which if you remember what cohesion is right, it's that protein holding the sister chromosomes together. Well another protein called separates comes in breaks that so the sister chromosomes can now separate and they do because they're pull pull towards each spindle pole. So um the first thing that happens is that the sister chroma tips begin moving towards the poles. Right? Then, the second thing that happens is the spindle poles actually move further apart. And so this not only are the sister chromosomes just moving with the micro tubules, but the spindles themselves are moving further so they're moving really far apart. And so um this is also where the ana phase promoting complex works, right? It's an ana phase. Do you remember we talked about this in the cell cycle control um that it works here to prevent to degrade some of these other proteins to prevent a repeat of mitosis for because it's coming to the end. So it wants to degree those things that are promoting it. So that's what happens in an A face. And then in tele phase, what you get is the nuclear envelope now is starting to reform the main topic, spindle is starting to disassemble and then things will eventually break into two cells. So here we have meta phase, you can see they're aligned in the middle, I like to think in middle in meta phase. Then um during an A phase, each one of the sister chroma tides is being pulled to the spindles as the spindles move forward to. So the separating the sister chroma types then in tele face, what you get is they keep moving and the nuclear envelope is gonna start reforming here the spindles are gonna start breaking down and eventually you're going to get two separate cells. So on the next page, I'm not gonna go through this just because it's exactly what I just went over. But there is a full diagram of the entire overview of mitosis with all these images together, starting here at interface, going through pro phase, pro meta phase, meta phase and a phase and tell a phase before breaking into two different sales here. So, if you want to review the overview of mitosis, make sure to come to this page and see if you can figure out what's going on without without the notes. So now let's move on.