so in this video we are going to be looking at the detailed mitotic cell cycle earlier videos we covered the mitotic cell cycle as an introduction okay but in this one we're gonna see every detailed stages that happens within the mitotic cell cycle and without wasting any time we immediately go into interface based on previous videos you remember that in the interface we will always start off with the newly divided cell dealing interface the newly divided cell will undergo two processes it will just become bigger the size of the cell increases and it will also double the number of DNA molecules pull a process known as dnf application now in reality the interface is actually further divided into three small stages the first stage in interface is basically a stage known as G1 all right now what exactly happens in G1 now if you see in my diagram over that I have put the cell on the left and also a mature cell on the right and on the cell on the left you can see the small little pink things like creeping things I hope you can see that I'm just representing that to be the mitochondria okay and so when you compare the newly divided cell on the left and the mature cell on the right and when it undergoes G1 phase what's the difference what has happened to the mature cell what has happened to the size number one you can see that the number of mitochondria in the cell has increased so that is actually what happens during the G1 phase the number of organelles within the cells increase it's not just the mitochondria it can also be the endoplasmic reticulum chloroplasts uh Golgi apparatus vesicles and such okay arribosomes and all I'm just representing mitochondria because I'm too lazy to draw everything else and what else also happens to the size of the cell you can also see that the size of the cell increases and this happens because the cell absorbs more water and the volume of cytoplasm increases so if an exam question asks you what happens during the what happens during the G1 phase during the G1 phase the number of organelles increase the size of the cell increases and the volume of cytoplasm increases and when it becomes a mature cell it is now able to carry out its specific function like I said uh like if it's a neuron it's able to send impulses if it's a muscle cell it's able to move things and if it's a white blood cell it's able to protect your body against infections now one very important thing to ask is how long does the mature cell remain as a mature cell it can remain as this cell for one day some cells can remain as a mature cell for two weeks some of it can remain as a mature cell forever and not decide to continue on in the mitotic cell cycle it really depends on the cell like for example if it's if this is like a skin cell the skin cell will just remain as a mature cell perhaps for maybe just um a day or two and then it will commit to the next part of interface some cells in your body will just remain SMH yourself forever and will not continue to divide that is just the nature of our body if it receives an external signal okay and the external signal says you need to divide okay you need to undergo mitosis uh then the material cell says okay fine I will need to undergo mitosis but before it undergoes mitosis it will then have to do the next part of interface which is known as the S phase and as you can see in the S phase the amount of DNA doubles which is a bit of revision why does the amount of DNA double well really simple so that when the nucleus divides each nucleus is able to get the same equal number of chromatins or DNA molecule it's as simple as that now an update undergoes DNA replication the mutual cell will then also undergo the final part of interface which is known as the G2 phase and in the G2 phase what exactly happens is any corrections to the errors of DNA replications are made so sometimes DNA of application is a dative application well is a or is an almost perfect process you know your the cell copies the DNA correctly but it's not like I said it's almost perfect it's not exactly perfect as you can see in the mature cell I'm drawing out the sequence of the DNA and then after DNA of application occurs there's a slight error in the base sequence of the DNA that ever has to be corrected it has to be rectified because if it's not corrected or rectified it may lead to some severe consequences later on uh for example it may lead to certain mutations which can cause problems in the cell function it may cause the cell to become cancerous there are a lot of consequences that can happen negative consequences that can happen if the error is not corrected so during the G2 phase any errors in DNA replication are corrected all right and also there will be an increase in microtubule production as you can see that also to run out the centurials uh remember ascentral such as this uh cylindrical structures and around the seventh Wheels you can see microtubules I hope you can see it in the video though it's like a small little orange lines and in the G2 phase there will be an increase in microtubule production as well now why is there an increase in microtubule production well the microtubules will later form something known as the spindle fibers and the spin the spindle fibers are needed to move the chromosomes around during the M phase the cell is now at the end of interface at the end of the G2 phase and it's ready to undergo mitosis now if you notice myself over here I've removed the mitochondria because while the mitochondria are important uh if I were to include them in the diagram it's going to become so confusing so I've removed them all right but just bear in mind that they are constantly that now so the cell is ready to divide its nucleus and that is when it's able to commit to the mitosis now before we go into mitosis of the M phase let's review the structures that is the nuclear membrane there are chromatin inside the nucleus that are also centrioles and also a reminder centrioles are only present in animal cells but not plant cells but the microtubules are present in both cells no so without wasting time let's go into the mitotic phase M phase now during the mitotic phase I'm the first stage of the mitotic phase or mitosis is known as the prophase I'm drawing out two cells over here one cell represents early prophase and one cell represents the end of prophase all right so I want you to look at these two cells and I want you to tell me what are the differences or What process happens during prophase so let's focus on the nuclear membrane first so what happens to the nuclear membrane well you can see that early purpose the nuclear membrane is there but at the end of prophase the nuclear membrane is gone so therefore the nuclear membrane has disappeared you can just say disappear or the nuclear membrane has broken apart now what has happened to the chromatin you can see that in early purpose the chromatin is there but at the end of prophase the chroma tins have condensed to become sister chromatids all right so when they become sister chromatids they are short and thick structures that are visible under the light microscope and the centrioles you can see that the centrals have moved to their opposite poles never ever see that the centrioles have moved to the top or the bottom or the centrals have moved up and down if I'm going another cell over that on the end of prophase in this case it looks like the central is on the left and also on the right but you will not see that during the exam never say that the sand Trails move up and down or left and the right you will just have to say that the centralials move to their opposite poles no matter how the cell is oriented now once they move to the opposite poles and this is the end of prophase so during the exam if the question asks you what happens during prophase you just have to mention the nuclear membrane disappearing the the chromatins coiling to become the sister chromatids and also the centralials moving to the opposite after prophase it will then enter the next phase which is known as metaphase now in metaphase you notice that this is the chromatase now line up along the cell equator some some of my students love to say they line up on the middle of the cell it does look like they are lining up on the middle of the cell right if I'm drawing another quick metaphase over that it does look like it's lining up on the middle as well okay because the centrioles are on the different ends of the poles uh we will never use the word middle we will still just use the word equator some books will say the sister chromatids line up along the metaphase plate that is also accepted as well all right but just use the word equator or metaphase plate never use the word middle of the cell and what happens next is the spindle fibers or the microtubules will attach to the central male of the sister chromatids and if you notice the spindle fibers which are made up of microtubules they're attaching to both sides of the sister chromatids and where I'm highlighting on this is the chroma tip that's the centromere now why are they attached to both parts of the centromere there's a reason for that the reason is because it's going to pull the sister chromatids apart because remember mitosis is all about separating the genetic material equally so when it pulls the centromias in the middle the sister chromatids will just break cleanly all right and we will see that in the next phase which is known as the anaphase so during interphase what happens is the spindle fibers shorten and they pull the sister chromatids causing them to separate so the sister chromatid was made up of two chromatids joined together but when it's pulled apart you can see that the chromatids have now been separated you have to show the inertia or the effect of the pole you kind of have to show that the chromatids are curved a little bit like they are being pulled what I mean by this is okay imagine if a person has a string or a rope attached to them and if You Yank the Rope or if you pull the Rope suddenly the person's body curves following the inertia of the pole all right so you can see that the person's like you know the legs are kind of facing forward the arms are also facing forward but the body is curved backwards right that shows inertia that the person is just pulled it's the same way with chromosomes as well when the chromosomes are poor they are shaped kind of Curves because of the sudden pull that happens in the cell you have to show that when they ask you to draw it if you were to suddenly we draw a cell and it looks something like this during the anaphase that is wrong because I do not see the chromatids curved it doesn't look like they are being pulled all right so the correction to that is you have to kind of I'm just you have to show it looking like this it does look like there's a curve over there it gives the illusion that they are being pulled well it's not an illusion because that's what's exactly happening in the cell right and the chroma tits we do not call them sister chromatids anymore because they're separated the chromatids now move to the opposite poles heading towards the centrioles and of course the last phase of mitosis is the telophase I'm not going to show you what happens okay you tell me what happens there are three phases of telophase the first part is the chromatids reach their opposite poles they are no longer being pulled the nuclear membrane will then reform in the second picture and the chromatids will now uncoil and at the end of telophase you have two nuclei that are formed after telophase that's the end of mitosis of the M phase and that's when it undergoes cytokinesis and during cytokinesis cell division happens and it will then produce two genetically identical cells all right which are newly divided cytokinesis in plant cells and animal cells uh is slightly different I will explain how they are different in another video all right not not this video all right as you can see here this is the entirety okay so I'm just zooming out of the mitotic phase or the M phase to just show you how the uh how everything happens uh it's too small but I still hope you can I hope you can still see them so what we're going to do is we are going to then draw out the cell cycle again but as you can see in this cell cycle it looks linear so I'm going to change the cell cycle to make it circular like they represent the textbook so we start off with a newly divided cell as you can see my newly divided cell I'm just drawing that gray area represents the nucleus the two small wet things represent these centrioles now for this cell just to make it simple I'm just going to draw two chromatins okay or two DNA molecules I know that in my earlier example I had four but just to simplify things further I'm just going to involve two all right because we want to make it easier all right to illustrate them all right so remember a newly divided cell will undergo G1 the size of the cell increases the volume of cytoplasm increases the number of organelles increase when the cell is told to undergo mitosis the cell will first do S phase and doing the S phase the number of DNA or the number of chromosomes double okay through a process known as DNA replication during the G2 phase the size of the cell increases further a little bit it may increase the number of organelles as well but the most important thing is it does any corrections to the DNA of application so errors in DNA replication or mistakes in DNA application are corrected these are the three stages of interface so the interface is made up of G1 s and G2 now during the mitotic phase how do we know the cell is doing mitosis well very simple because you are able to see the sister chromatids all right you'll be able to see it in the prophase where the centrioles have moved to the opposite poles and the chromatins have condensed to become sister chromatids which are visible under like microscope during metaphase the system chromatids will line up along the Equator and the spindle fibers attached to the centromia during anaphase the spindle fiber shortened and this is the chromatid separate and the individual chromatids move to the opposite poles you have to show that they're being that they are being pulled right by curving the shape of the chromatids and doing telophase I will just skip the steps of telophase but during the end of telophase we know that two nuclei are visible within the cell that is the end of the M phase of the mitosis and after that cytokinesis basically happens and you get two newly divided cell all right so I'm just labeling all these structures here bear in mind that the cell spends most of its time in interface okay and within interface it spends most of its time in G1 and G2 it spends a short amount of time in the S phase by the way okay the mitosis doesn't take a long time cytokinesis doesn't take a long time okay so the cell spends at least about we can just on a rough estimate about 75 about 75 percent of its time or even more actually in interface all right so this is the entirety of the cell cycle and I hope it's quite detailed for you