Video: Cell cycle and mitosis

﻿Hello everyone, welcome back to Combine Science for key stage four. This is Miss Wong with you again in cell biology. Today, we're looking at cell cycle, mitosis and how this mitosis process is linked to growth and repair of the human body. Now let's have a look at the equipment that you will need in this lesson. In this lesson, you will need a pen, paper or books to write on. And please also switch off your phones, close all the other browser tabs. If you need more time to do that, pause the video, make sure you have switched off your phone and closed all browser tabs and then come back to this video. Now, we would like to look at the agenda. So we're going to look at the cell structures again. Then we're going to talk about the cell cycle, and then we're going to talk about mitosis. And of course we will build in some exam questions so that you can practise. First of all, let's have a recap on the cell structures. On the board here, you are shown a cell. I would like you to pause the video and write down the names of structure A, B, C, and D. Pause the video now and resume the video when you're ready to check your answers. Make sure you've written down your answers. And now we are going to check. A is cytoplasm. B is nucleus. C is cell membrane. And D is mitochondrion. If you have written on mitochondria, that's also correct. I would like you to check your spelling as well. I would like you to highlight the membrane, the spelling of cell membrane and the spelling of mitochondrion you've got them wrong. And if you're ready, we can move on to the next slide. We're going to talk about cell cycle and mitosis. It is very important for us to remember the structures of the eukaryotic cell, which is the animal cell that we've just gone through and really link that cell structure into today's topic. Let's have a look at the diagram on the board. We are going to talk about the genetic material. And for an eukaryotic cell, you'll find the genetic material inside the nucleus. Let us look at the cell here. So in the middle, you can see the nucleus. And if you go into the nucleus, you'll be able to see some chromosomes. So chromosome is basically a structure of DNA coiled around proteins, and we call them chromosomes. So chromosomes is not only DNA, but DNA coiled around proteins. And even if I zoom in more, we will be able to see the DNA as a double helix going down like this. Of course, the DNA is really long I cannot show you all the length of the DNA in this diagram. And if we only look at one session of the DNA, we call this the genes. So we've got many genes linking with each other to give you the whole strand of DNA. In this line what I would like you to pay attention to is the relative size of these objects. So a cell, even though it's small, it's much bigger than the nucleus. And the nucleus is already very small, but the chromosomes are even smaller. And then of course, the DNA is very long, but it's very, very small inside as part of the chromosomes. And then one session of the DNA is called the gene. So a gene is even smaller. Now, I would like you to pause the video and complete this task here. I would like you to arrange the following from the smallest to the largest, according to their sizes. Pause the video now, complete the task in your books and then resume the video for the answers. Let's have a look at the answers. So among all of these, the largest is of course, sorry, the smallest is of course the gene. And then you want to go for the second smallest, which is at the end of the double helix, we have the chromosomes come up next and then nucleus and then an animal cell. It is really important that we know the relative sizes and we know that the cell is microscopic and the nucleus, the DNA and the genes are very, very small stored inside the cell. So for all cells to make copies of themselves, they would go through a process called mitosis. We want to think about the mother cell splitting, dividing into two daughter cells. We call the mother cell a diploid mother cell, meaning that the mother cell has a full set of DNA. For human beings, the diploid mother cell has 23 pairs of chromosomes, which is the equivalent to 46 chromosomes. In the process of cell division, the diploid mother cell would replicate the whole set of DNA. So let's say from 46 chromosomes, it will go into 92 chromosomes after replication. And then the cell division involved is called mitosis and it was split the cell into two identical daughter cells with the sex same genetic material. And therefore the daughter cells are also diploid because each of them also has one full set of DNA. So all the cells will go through a cycle. So mitosis as a type of cell division does not occur all the time. The cell needs to go through a cycle to prepare itself and then divide, and then come back to the preparation phase. Let's have a look at this cycle. First of all, the cell needs to grow. The cell needs to grow bigger because it is going to duplicate. That means to make a copy of the organelles, for example the mitochondria, for example the nucleus, before they can divide. And it is necessary for the cells to grow bigger so that it has space to contain all that duplicated structures. Then the next stage is DNA replication. So for one cell to produce two daughter cells, it has to replicate. That means to make a full copy of all the DNA inside the nucleus. And it also takes up a lot of time too. After that the cell will go into the preparation phase for mitosis. And then, mitosis happens and one cell separates into two daughter cells. So what separates will include the nucleus, will include the cytoplasm and the cell membrane. So after this stage, you should have two identical daughter cells, and then the cell will enter the grow phase again. And if it's mature, if it's big enough, it's ready, it will go into DNA replication, it will prepare for another mitosis and then another mitosis happens. So this is a cell cycle. A lot of cells will go for this cycle and therefore we have new cells formation for growth and for repair. Now, I'm going to go through the details of mitosis and I will switch to our whiteboard. So we are going to look at the details of mitosis here. This is an animal cell. So this is the cell membrane, that's nucleus. But to show you the process of mitosis, I will have to do a bit of an unrealistic diagram. That is, I'm to show you what is inside the nucleus. So I will just rub it off and then I'm going to illustrate the chromosomes on this whiteboard here. So what is going to happen is I need to draw other chromosomes. And to keep it simple, we will just assume that this haploid mother cell has a very simple DNA structure. Which means it has two chromosomes. So you can see one is black and one is brown. The cell will need to grow bigger and to replicate its DNA before it can go through mitosis. So the first stage will be, the cell needs to replicate everything inside the cell. So, and it has to grow bigger. For the sake of space I can't really illustrate that it grows really bigger, but it looks bigger here. And of course it has duplicated DNA. So, from having one black chromosome, now it would have two black chromosomes. And to replicate the brown one as well, so instead of having one, it will also have two brown chromosomes. So at this stage, going from two chromosomes, now it has doubled the genetic content and now it has got a total of four. So the cell, will be ready for mitosis. So when mitosis happens, you'll see the chromosomes being pulled to both ends of the cell. So the cell will still look like this, but the chromosome will be pulled to both sides. So the black ones are here and the brown ones are here. And what happens is, there will be tiny and little microscopic fibres that we call them spindle fibres, pulling them to the ends of the cell. So these two spindle fibres will pull that way. These two fibres will pull this way and the chromosomes were moved to the opposite ends of the cell. And then, you should be able to get two cells. So if it splits like this, so you should get one cell at the top with one black and one brown chromosome, and you should have another one, another daughter cell that has one black and one brown chromosome. Now I would like you to look at the genetic content. So from two, it has replicated the DNA, and then you should have now four in total. So it has doubled. The event after the division, after mitosis, you have two daughter cells, and each of them has two chromosomes, which is one black one brown, one black one brown, and they are identical. And if you look at where these two cells came from, which has that one, the mother cell, they all have two chromosomes, one black one brown, one black one brown, one black, one brown. So this is the process of mitosis producing as identical daughter cells. The daughter cells themselves are identical, and they're also genetically identical to the mother cell. But again, I would like you to think about this diagram as just an illustration. Why is because normally, these chromosomes should be inside the nucleus, but I cannot draw out nucleus over here. And the second point I would like to make is we have way more chromosomes than two chromosomes being shown in these diagrams. I drew two just because it's very clear, very easy to illustrate. We need to remember that in a human body, our human body cells, excluding to reproductive cells, we always have 46 chromosomes. So realistically, I can do this. So let's assume that I am going to replace the numbers, with the actual human body cell chromosomes numbers. We should start with 46 chromosomes at the beginning. As DNA replication would double that to 92 chromosomes. And then when mitosis happens, it divides to give us again, 46 and 46 in each of the daughter cells. I hope this is helpful. And now we will go back to the PowerPoint presentation. Here on the board I'm going to show you a more realistic diagram of the mitosis process. This is a picture taken under the microscope, and it shows you very clearly that the chromosomes are separating. We're going to look at, first of all the cell in the middle. You can see that the nucleus is very dense and you can see that there is something happening but you cannot tell exactly what's happening. Probably, the cell is preparing for mitosis or is duplicating the DNA. So this stage is not very obvious, but you do see the chromosomes condensing and becoming more obvious under the microscope. And then we are going to look at the top left. This cell is very, very clearly showing us that the two sets of chromosomes are being pulled to opposite sides. After that, this cell is going to separate into two daughter cells with the identical set of DNA. And therefore, I can conclude that this cell is going through mitosis at this stage. Now let's do a multiple choice quiz. I would like you to think about which phase is the longest in the cell cycle. The answer is growth. The cell needs to grow to a size big enough to accommodate all the new structures that will be formed after duplication. Let's have a look at the next question. Which phase is shortest in the cell cycle? Read the answers and pick one of them as your answer please. The answer is mitosis. Mitosis is the shortest in the whole cell cycle. What is or are the product or products of mitosis? We have four options on the board. I would like you to read them and pick one as your answer. Well done, if you have got this as the answer. It should be two identical cells. Again, one mother cell is going to form two identical daughter cells. Last thing I want you to think about why mitosis is important. You have to pick two from the board. So the answer is for growth and for repair. I hope you've got them right. Lastly, we would like to go through some exam questions. So it would give you an idea of how the exam will assess you on the topic of cell cycle and mitosis. Pause the video now. Since you've resumed your video, let's check the answers. So you would want to write down. The chromosomes were separated from each other and moved to the opposite ends of the cell. So they get pulled to both ends of the cell to separate into two identical daughter cells. We would like to look at the final question that we would like to work on. This is the last exam question. Noel investigates the growth of onions. He puts an onion bulb in a jar of water. The bulb starts to grow. I would like you to answer the question down below. What is the name of this type of cell division that allows the growth of roots? Write down the answer which is one mark. What's the name of this type of cell division? I hope you've got this one right. The answer is mitosis. Again, mitosis is for growth and repair. So when plants, when an animal gains mass, gets more new cells, it's because of mitosis. Today we've talked about mitosis and cell cycle. We've talked about the process of a cell preparing for mitosis. And we also talked about the length of different stages of the cell cycle. Of course, we also looked at why mitosis is important. Again, I believe you can answer me now that mitosis is important for two things. The first thing is for growth, and the second thing is for repair. I would like you to proceed to the exit quiz now, and also proceed to the independent practise. It's very important that you complete all the questions and check your answers after. Thank you very much for joining me today, and now I'll see you in the next lesson.

Worksheet: Cell cycle and mitosis

Exit Quiz: Cell cycle and mitosis

Completed: Cell cycle and mitosis

This lesson will take you through the structure of a simple eukaryotic cell and how one cell can divide into two identical daughter cells by mitosis.

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Cell cycle and mitosis

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