Free Biology NEET Video Lectures for Cell Cycle And Cell Division

00:00:39 [Music] Hello friends, welcome to today's session myself PGT bio from KVKUR. Today's content is regarding cell cycle and cell division. First of all to the introductory session which is the life activity that leads to continuity of life. Without that life activity, not even a single species is able to continue its life. You know the answer? Yes, of course there is the reproduction and you know in reproduction there are two different types. What are the two different types of reproduction? Again your answer is

00:01:49 correct. Sexual and asexual reproduction. What is the mechanism of reproduction that is seen in a unicellular organism? Yes, it is with a cell division. You know for linking one generation to another generation there needs a single cellular and deployed structure and that will act as a vital link. So what is that vital link that links one generation with the other generation? You know it is zygote. Again you know the phenomenon of formation of zygote. Which phenomenon or which process that results in the formation of

00:02:55 zygote? Yes. Fertilization. Fusion of male and female gamts. Is there any other term for this? Yes. Singami. Now how many cells are there in a zygote? There is the fusion of male and female gia means two cells are fusing. So how many cells will be there in a zygote? Yes, your answer is right. Only one cell. How is zygote then develops into a multisellular organism? An interesting fact. It is only by cell division. Without cell division, zygote can't give rise to a multisellular organism. How the body of an organism

00:03:56 grows. You consider your own case. You yourself developed from a single cell zygote and now the grown-up body. So how the body of the organism grows? Of course, it is by the phenomenon again cell division which in life process leads to repair and regeneration of damaged tissues. If there occurs any damage in any of the tissues then it must be repaired and you know in of the organism some of the parts are regenerated. The lost body parts are regenerated. And the phenomenon here also it is cell division. Is cell division occurs in

00:04:50 sexual and asexual reproduction? Yes, of course. For asexual as well as sexual reproduction, there needs the phenomenon cell division. Now coming to what is cell division? Cell and division that means division of a cell into two or many daughter cells. The basic process involved in cell division. One cell growth that is synthesis and duplication of the components of the cell. Second cell division adult cell that will divides into two daughter cells. Now coming to the different types of cell division.

00:06:03 One is amitosis. The other is mitosis. Third one is miosis. So how many different types? Yes, three different types of cell division. A mitosis, mitosis and miosis. Now coming to the stages of cell division. It is not a simple phenomenon. It is not a singlestep process but it consists of different steps. We can include these different steps into two major headings. One is karaioinosis. Carryon means nucleus. Kinosis means division. So kiochinosis means division of nucleus. The second phenomenon that is called as

00:07:03 cytochinusis. Again cyto refers to cytoplasm. Kinosis means division. So it means division of cytoplasm. Here the first phenomenon for division each and every cell has to undergo cell cycle. Cycle cyclic events a series of events series of events cyclic events by which a cell prepares for cell division and this particular series of cyclic events by which a cell prepares for cell division that is known as cell cycle. Now what are the different steps in a cell cycle? The first phase we can call it as

00:08:06 interphase. Second phase is known as M phase. Here you can see the picture of a cell cycle. It consists of again different stages. The interface the stage between two cell divisions where the cell is preparing for cell division. So it is not a resting stage. It is not a metabolically inactive stage. Whereas it is a preparatory stage and by this stage the cell is preparing for cell division and it is a metabolically very very active stage. Commonly it is known as resting stage. It is a misnomer. It is not a resting

00:09:13 stage. It is metabolically highly active stage and it is the longer stage in the cell cycle. It will last for about 95%age of the cell cycle. So this particular stage we will call it as interphase. Now coming to the different stages of interphase. Here you can see the diagram. G1 phase then S phase then comes the G2 phase. G1 S and G2 collectively known as the interface. Then again you when you are observing this diagram you can see that after these three stages G1 S and G2 there comes yet at another phase that we

00:10:18 will call it as Mphase with different steps such as prophase metaphase anaphase followed by cytochinosis and Here there is one more stage represented that is G0 phase. Some of the cells even after this preparation they are entering back to G0 stage co stage remains inactive. So in short an interface which consists of three different stages G1 S and G2. So these three stages or phases together known as the interface. Now coming to the first one G1 phase G represents what? Yes. Gap phase or growth

00:11:22 phase. Gap one phase. It is the post mitoic phase. This is Mphase or mitoic phase. Again G1. So it is post mitoic phase or yes. You see here in the in this cell cycle here you can see S phase and before this S phase what you can see yes G1 phase. So this G1 phase that is known as preynthetic phase. So synthetic yes refers to synthetic phase. So before that synthetic phase it happens. So it is known as pre pre means before pre synthetic phase. It is also known as growth phase. G1 phase. G4 again growth one

00:12:29 first. So it is known as the first growth phase. And again it is the period between mitosis and DNA replication. During this S-phase there occurs DNA replication and mitosis or Mphase the stage between Mphase and DNA replication phase S-phase. What are the events that takes place during this stage? You see here enzymes and proteins some of the proteins and enzymes that are synthesized during this stage. Similarly, synthesis of RNA molecules, carbohydrates, lipids and pooling of amino acids and nucleotides. By using these amino acids,

00:13:31 it can make the nucleic acid molecule. That means different types of RNA synthesized. Then coming to the next point that is when all these things are synthesized in a cell naturally the size of the cell will increase. Of course the size of the nucleus will also increase. A cell in the G1 phase can undergo any of the three options. First option can enter into the next stage. What is the next next stage? Yes. Phase and then it can divide. Second option. It may be arrested at any specific point in the G1

00:14:28 phase itself. It can be stopped. The third option is it may stop cell division and it can enter into G0 stage and that G0 stage is known as coent stage inactive stage. These cells can again enter back to G1 stage and it can starts just like that of a normal cell depending upon the requirements. So, SL in G1 phase can adopt any of the three options. Now coming to the S phase. S for synthetic phase. Synthesis. What is synthesized here? Yes, DNA is synthesized. DNA replicates. DNA get doubled. Each chromosome has then two

00:15:49 chromatids. Then in addition there needs some of the other basic proteins for example hyone. So synthesis of that basic proteins mainly histone will also takes place during this syn synthetic stage. Yes s face phase chromosome number remains the same. Even though the chromosome get doubled and each chromosome has two chromatids the number of the chromosome remains the same. Now coming to the next stage that is G2 stage. Second gap phase or Gab second phase. Second growth phase also it is correct and it is the stage that is

00:16:43 coming after the synthetic phase. So known as post post synthetic phase and this is G2 phase when you are observing this particular diagram you can see that it comes before the M phase or motic phase. So we can call it as yes premiotic phase synthesize spindle proteins. The proteins needed for the formation of spindle fibers that are synthesized during this stage. Moreover, there is the synthesis of different types of RNA molecules. synthesis and the storage of ATP molecules. Duplication of the

00:17:54 centrialsles as well as the different organals needed for cell division. increase in the size of the nucleus. So by the synthetic activities the size of the nucleus and size of the cell will increase. Now coming to the next phase that is Mphase M4 mitosis mitoic phase or even division division phase. It is the stage you can see here comes after these three phases. What are the three phases? G1, yes. And G2. You know what term we will give for these three phases together? Yes, of course it is interface. So it is the stage that is

00:18:50 coming after this interface. So stage that follows end of phase that is the M phase or motic phase and during this stage M phase you can see that the nucleus will divide followed by division of cytoplasm. So the division of a nucleus we will call it as kyocchinosis and division of cytoplasm we will call it as cytochinus. Now coming to the duration of the cell cycle whether all the cells are having same duration. No it varies. It varies from cell to cell and it also depends upon some of the external

00:19:44 factors such as temperature, food and even oxygen supply. Now here are some of the examples. Bacterial cell the duration of cell cycle is 20 minutes. When it comes to human cell, the average is 24 hours. East cell it goes to 90 minutes. And the intestinal epithelial cell it goes to 80 to 10 hours. So the cell cycle duration that will vary from cell to cell. Here comes yet another type of cell division amitosis. It is a simple method of cell division or it is known as direct cell division. There is no synthesis of

00:20:56 spindle fibers. There is no coiling and condensation of chromatin fibers. Nucleus elongates and divides into two. Nucleus of the particular cell that underos amitosis. It will elongate and divides into two. And after this nuclear division it is followed by division of cytoplasm. And this type of cell division it takes place in the primitive type of organisms mainly for example bacteria, yeast, amoeba and it can even takes place in the cartilage cells. So it is the simplest method of cell division or even direct method of cell

00:22:01 division. We can call it as direct cell division followed by by elongation of nucleus and then followed by division of cytoplasm. Here is the method you can see nucleus it elongates and divides into two by the division of cytoplasm. Now coming to the mitosis. The term mitosis that was coined by W. Fleming discovered by Strawber in plant cell and W. Fleming in animal cell. It takes 30 to 3 hours to complete. In human somatic cell, it takes 3 hours. It takes place in somatic cell or even in body cell.

00:23:15 So the cell division that takes place in the somatic cell or in the body cell that is known as mitosis. It is known as equational division. Why it is known as equational division? Because here after the cell division we will get a two daughter cells and these two daughter cells are qualitatively as well as quantitatively remains the same. Moreover the chromosome number regarding the DNA content chromosome number and all it will remains the same as that of the parental cell. So this particular division mitosis it

00:24:08 is known as equational division. It helps in growth, repair and regeneration. Here comes to the stages of cardioinosis. Here also the cell will divide by karaioinosis followed by cytoinosis. The different stages of karaogynesis. You know what is karaioinosis? Yes. It is the division of nucleus into two. The different stages here are prophase, protetaphase, metaphase, anaphase and tilophase. So here there are five different stages proase, pro metaphase, then metaphase, anaphase and tilophase. Here you can see some of

00:25:20 these diagrams also proase stage and this is the metaphase stage. In between these two stages prophase and metaphase there is a short stage a transition stage that is called as pro- metaphase. This is the anaphase stage and this is the tilophase stage. Now we can see what happens in each of these stage. What are the changes? What are the events that takes place in each of these stages of carioinosis? First one that is profit. Here you can see the diagram. Go through this diagram and try to identify

00:26:12 the changes, the events, the characters. First one, disappearance of centrosphere. Centrosphere, you know what is centrosphere? The area, the clear area that surrounds the centrialsles. So that centrosphere area disappears. Then what happens to this centriole? What is this particular structure? Centriol. What happens to the centriole? It get doubled. Senriol pairs doubled and it get moving to opposite poles. It started moving to opposite poles. You can see very clearly in this diagram movement of the

00:27:00 centrialsles. Now from each of these centrialsles you can see some of the rays fibers they are originating and we will call these as astral rays around the centrial. The astral rays start developing and these are the proteinious microtubules. Now what happens to this chromatin reticulum? Chromatin reticulum that under goes two phenomenon. One is coiling. You know when a structure coils it get condensed. So it under goes coiling and condensation to form chromosomes. Now each chromosome when we are

00:27:58 observing we can see that it has two chromatids. I'll show you here the diagram also. Here you can see the chromosomes. Each of these chromosome has two chromatids. And this chromatin reticulum seen in the resting phase or even in the interface that under goes coiling followed by condensation and they forms the thick road-shaped structures. We will call them as yes chromosomes. Each chromosome there is two chromatids. And here you can see these two chromatids they are seen attached at the centromeir. And during this mid prophase

00:28:59 stage, midphase of the prophase chromosomes undergo further coiling and condensation. Again the chromosomes under goes coiling and condensation. That process continues and finally it becomes a thick and roadshaped structure. Here you can see in the later phase of this proface and compare this one with the early prof stage there is huge difference. Here these are appearing as even threadlike structure but here it becomes highly condensed thick roadshaped structure. We can call this as chromosomes and clearly you can see the

00:29:42 chromatids distinct chromatids you can see clearly. So they becomes more and more thicker and they becomes shorter and such thick and rodshaped chromosomes we can see here in the late profess. Now what happens to this nuclear membrane? Here you can see an or intact nuclear membrane in the early pro stage. But what happens in this late phase you see go through this diagram the nuclear membrane that starts disappearing. It can be seen represented here as a dotted line only. Here it is an intact line in the form of a definite

00:30:28 circle. So here the nuclear membrane starts to disappear. Now see these two diagrams. What happens to the nucleololis here and nucleololis here in the early prophase stage when you are observing you can see here the nucleus clear nucleus you can see it is visible but what happens to this in the late prophase you can see here as the dots only it means it is disintegrating going to starts to disappear here. Now in a late process there occurs further coiling and condensation of the chromosomes. I have

00:31:17 already told you this coiling and condensation of the chromosomes. It is a continuous phenomenon and it goes on and finally we will get a highly thickened roadshaped structures with the two clear chromatids. We will call them as chromosomes. Now you can see the aers. What happens to these aers? The centrial with astral uh rays they have reached the opposite poles during the late profile stage. Formation of spindle fibers again you see compare these two diagrams here formation of spindle fiber starts. Here

00:32:04 it is almost completed. You can see here the spindle fibers that is connecting with these chromosomes. So formation of a spindle fibers takes place a and spindle fibers we will collectively call it as motic apparatus. You can see here the labeling centrial the the rays that is aster and here you can see the well-developed spindle fibers. So this aster plus spindle fibers we will collectively call it as the motic apparatus. Now when we are observing here we can see that there are different types

00:32:57 of spindle fibers. One is the chromosomal or discontinuous fibers. The other is continuous or inter polar fibers. Here you can see these different types of spindle fibers. You see some of these spindle fibers they are attached with this cendrome of the chromosomes and some are moving from one pole to the other from one centriole to the other without attaching these chromosomes. So such fibers the the spindle fibers that are attaching with the centromeir of the chromosome they are known as chromosomal

00:34:05 fibers. Here also you can see the chromosomal fiber and in between these two there is at another one that is the interzonal fiber. It will link the centromeir of one chromosome with the centromeir of the other chromosome. Indzonal fiber and at the same time the third one that is continuous fibers moving from one pole to the other one central to the other continuously without attaching the uh cendrome of these chromosomes. So continuous fibers extend from one pole to the other. Here you can see continuous fibers that is moving

00:34:53 from one pole to the other. So they are called as interpolar fibers. Inter means in between. So in between the two poles in between the two centrialsles you can see this particular fiber moving. So it is known as interpolar fibers. Now here the other one that is called as discontinuous fibers they will extend from pole and connect with the cendrome or chromosome they are extending from pole and they will connect with the centromeir of the chromosome. This one they are known as discontinuous. So since they connected

00:35:41 with this endrome of the chromosome we can call it as chromosomeal fibers. Now coming to pro metaphase here you can see this uh diagram clearly. Pro metaphase a short stage. It is a short stage before metaphase. Pro means before and it is the stage after prophase. So the stage between prophase and metaphase. There is a transition stage a very short stage that is known as protaphase. During this stage, chromosomes lie irregularly. See the diagram. Some are near the pole, some are in the middle like that. The chromosomes are seen

00:36:43 irregularly on the spindle fibers. Chromosomes are moving towards the uh equatorial plate of the cell. Equator that means center of the uh cell. They are they started moving but they have not reached the some have reached even in this endor and some are approaching like that irregular arrangement. Here you can see the next stage that is metaphase. Chromosomes are highly condensed one, highly thick one, highly coiled one. You can see it clearly even you can count it clearly also during this metaphase stage. They are highly

00:37:28 condensed and thick one with a clearly uh the chromatids each chromosome with the two distinct chromatids attached on the centromeir position. So you can identify it clearly and even you can count it also each of these chromosome as I have already told you with the two distinct chromatids. All the chromosomes see what happens to their arrangement where you can see exactly at the center of the cell that is called as equatorial plate of the cell. So this is the typical character of a metaphase stage. Highly condensed thick

00:38:14 chromosomes with a distinct chromatids arranged at the equatorial plate of the cell. So this particular character shows the typical character of a metaphase cell. Now what happens to this spindle fiber regarding its formation? Spindle fiber formation is completed in this stage. Each chromosome that is connected by two chromosomal fibers. This is one chromosomeal fiber starting from one pole and this is the other chromosomeal fiber that starts from the other pole each from each pole and they are

00:39:05 connected at the centrome part of the chromosome. Cendrome of all the chromosomes you observe centromeir of all these chromosomes they lie in the center equator equatorial plate. Now the arms arms of the chromosomes are pointing towards the poles. Yet another identifying feature centromeir will be at the center or even equatorial plate of the cell and arms are pointing towards the poles. Now coming to an stage. Here you can see the anaf stage diagram. It is the shortest stage which takes 2 to 3 minutes

00:39:57 time. Spindle fiber that will contract. The contraction of a spindle fiber takes place. Now what happens when the spindle fiber contracts the centromeir of each of the chromosome will divide. Centromeir of each chromosome that will split that will divide and each chromatid will move to opposite poles. Here you can see the chromatids and these are the centrome. So it will move to opposite port. The two sister chromatids we will call it a sister chromatid. The two chromatids of a of the same chromosome

00:40:42 that we will call it as sister chromatid. Here also you can see the diagram clearly or uh the chromatids these chromatids are carried into a positive poles not the entire chromosome as such. So the chromosome with the two chromatid that will divide at the centromeir portion and it is moving to opposite poles here. The proteinious interal fibers. This is what is called as the interzonal fiber. And this endzonal fiber developed between the centromeir of daughter chromosomes. Daughter chromosome means the separated

00:41:41 chromatids. Centromeir of each daughter chromosome. See the diagram. Centrome of each of these daughter chromosome that is pointing towards the poles. Now what happens to the arms? arms are pointing towards the center. So this is the arrangement seen in the anaf stage. So this type of arrangement of chromosome and this particular stage that is anaphase and arrangement based on that arrangement we can identify the stage. So centromeir of each of the daughter chromosome or chromatid that points towards the

00:42:28 poles and arms are pointing towards the center identifying characters. We can see equal number of chromosomes data chromosomes in each of the pole. Here you can see 1 2 3 four four chromatids or we can say daughter chromosomes. Here also you can see four chromatids or daughter chromosomes. So in each pole we can see equal number of daughter chromosomes in this stage. Now coming to the tilophase stage and during this stage it takes around 1 hour to complete. It is just the opposite of prof stage. The changes that takes place just

00:43:37 opposite to the changes happened in the profit stage. Chromosomes starts uncoiling. You know in prophase stage the chromosomes started coiling and condensation. Just the reverse chromosomes starts uncoiling and decondensation. Then what we will get? We will get the thin chromatin threads. We will call it as chromatin reticulum. Now what happens to these astral as well as the spindle fibers that will disappear. Now centrioles that is surrounded by the centrosphere the clear area and forms centrosome just opposite to that of

00:44:31 prophase stage. Here you can see the diagram in this particular diagram to face nuclear membrane reappeared during the process stage it starts disappear and by the end of the procase stage it is totally disappeared here it reappears. Now you can see this blue colored structure that is the nucleololis. So this nucleolus also reappears. In profile stage it disappeared but here it reappears. And we can see one nucleus in each of the pole of the cell. Now coming to the next stage. What is the next stage? Carioenosis is over. Prophase,

00:45:33 promophase, metaphase, anaphase and the toophase. Now what is the next stage of division? Yes, it is the cytochinus. Cyto refers to cytoplasm. Kinosis means division. So what is cytochinosis? Yes, it is the division of cytoplasm. Now is there any change in the cytochinosis of an animal cell with that of a plant cell? Yes. In animal cell it is by cell furrowing the cell plasma membrane that produces a narrow inrowth invagination at the middle of the cell. And later this particular invagination in growth that or the furrow that

00:46:36 deepens and it will meet together and it will divide the cytoplasm into equally into two. Here you can see the same phenomenon of a cytochinosis but it it is in the plant cell. So in animal cell it is by cell furrowing invagination or furrow formation or by the plasma membrane exactly at the center of the cell. Furough deepens meets together and divides the cytoplasm equally into two. Here it happens by yet another method that is known as cell plate formation. So in plant cell the cytochinus is by yet another method that

00:47:31 is by cell plate formation. Here you can see some of the fragments fragments of endoplasmic reticulum some of the vesicles from the GGI bodies and the fragments of a spindle fibers. All these are arranged at the equator of the cell arranged at the center of the cell in between the two nuclei. And these structures, these fragments, these pieces, they are collectively known as fragmoplast. We can say them as or call it as fragmoplast. And these fragmoplast they will fuse together and form the cell plate.

00:48:21 All the components of the fragmoplast fuse together and forms the cell plate. It grows on both of the sides and unite together and it will forms the middle lamela. Lamela means layer middle layer. Later on cellulose, hemiselulose and other molecules are deposited over this middle lamela and it will form the cell wall. So by this method the cytoplasm of the cell that is divided into two equal components parts. So we will get two daughter cells equally we will get two daughter cells. So in short the

00:49:23 cytochinosis division of cytoplasm in plant cell and in animal cell there is difference in animal cell it is by yes cellarrowing and in plant cell it is by cell plate formation. Now why there occurs this mitosis? What is the need of this mitosis? What is the significance? What is its relevance importance? So it keeps the chromosome number constant in all the daughter cells. Suppose if it is 46 in the daughter cell also it will be 2n equals 46. It helps in growth and development of the zygote. You know zygote is formed after

00:50:13 fertilization after zingami after the fusion of male and female gametes. It is only a single cell. Even though it contains two set of chromosome deployed it is only a single cell. We all developed from that single cell called a zygote. So how it is possible? We are the multisellular complex organisms. How it is developed? How it is possible? The one and only option is by mitosis. The cell division. It helps in repair. If some of the tissues get damaged, if some injuries takes place, it must be healed up. It must be

00:50:55 repaired. New and new cells must be added. So for this purpose there needs mitosis and similarly it helps in regeneration regeneration of tissues from the lost parts. It helps in a sexual reproduction and similarly it is restores nucleoplasmic ratio the amount of or the ratio between nucleus and the cytoplasm that is restored even in the daughter cell also as normal equal. Now see the differences between mitosis in the case of a plant cell and that of an animal cell. You see plant cell there is there won't be any

00:51:55 centrialsles. Centrialsles are totally absent in plant cells but it is present in the animal cell and no aster formation since endrolles are absent no astral rays here aers are formed here you know cell plate is formed for cytochinus in plant in animal cell there won't be any cell plate formation No cell phoning here. Cytochinosis takes place by cell plate formation not by cell phoning. But in animal cell plate formation it takes place by cell furrowing. In plant cell no cellaring but it takes place by cell plate

00:52:52 formation. It occurs mainly in the merist stems here occurs in tissues throughout the body. Now coming to meiosis the second cell division or rather we can say the third type of cell division. First one mitosis then amitosis then the third one that is miosis. Who discovered meiosis? You know Van Bendon discovered mossis and it was described by Vinnie water. The term meiosis that was coined by farmer and more. It replaces in the repro it takes place in the uh reproductive cells. or even germ cells, pollen mother cells, megaspore

00:54:00 mother cell that means it takes place in the deployed cells. MioC is known as reduction division. Chromosome number is reduced into half in the daughter cells. Here what are the changes takes place here? also DNA must be duplicated. DNA duplicate only once but the cell divides twice. Nucleus will also divides twice. Since it divides twice, we will get four different four daughter cells. It helps in sexual reproduction. It results in the production of hloid gamines and it will maintain the chromosome number of a particular

00:54:52 species constant in each and every generation. Now I have already told you there are two stages of meiosis. One is nucleus divides into uh divides twice in this stage meiosis one or first nuclear division and the other one is known as meiosis 2. So here in meiosis one there again karaioinosis nuclear division followed by cytoinosis. Carioinosis has different stages prophase one metaphase one anaphase one and tilophase one. This one we are writing because it is the first nuclear division of miosis.

00:55:47 Now here are some of the questions for you to think and answer. See the first question. What is the average span of cell cycle in a mamalian cell? Distinguish cytochinusis from karaioinosis. Describe the events takes place during end of phase. What is G0 of the cell cycle? Why is mitosis called as equational division? Name the stage of cell cycle in which the following events takes place. A chromosomes are moved to the spindle equator centromeir splits and chromatid separate. How does cytochinosis of plant cell differ from

00:56:45 that of an animal cell? Can there be mitosis without any DNA replication? remaining aspects we will see in the second session. Thank you. [Music]