Understanding Telomeres and Cell Division

in one of the earlier videos we were looking at the structure of the chromosome and we noticed that the chromosome has a few different structures they have the centromere telomeres and the genes so in that previous video I said that we'll be talking about the telomere in a later time that time has now come now before we talk about telomeres in detail we want to start ourselves with a simple situation okay and this is a question that I love to ask my students now imagine if you took a skin cell out of a person's body right and a skin cell is a very interesting cell that can undergo mitosis if it wants to if you stimulate it to undergo mitosis now if you were to put the skin cell in a petri dish and you were to stimulate the skin cell to undergo mitosis you gave it all the nutrients and substances it requires the cell will undergo mitotic cell cycle repeatedly okay so just basically undergoes mitosis from one skin cell it produces two four eight and it just keeps going on now but the question is does it go on forever and does it just continue undergoing mitosis now some of my students say yes but my other students will say no because they will run out of nutrients in the battery dish which is a pretty good answer all right but then I'll ask my students another question where I say assume that the nutrients were not a limiting factor so we assume that the nutrients were constantly that there was sufficient nutrient for all the cells will the cell then continue to undergo mitosis until you have a colony of skin cells growing like a monster covering the floor is this basically glowing mitosis and it's just the colony of skin cells is becoming larger and larger and larger until it covers the entire Earth well the thing is it doesn't because assuming that a cell we start off with the cell as the first generation and every time it undergoes mitosis it becomes the second generation so third generation so on and so forth um when this cell especially a skin cell reaches for example the 20th Generation all right the cell will just die now the cell dies not because of a lack of nutrient it just does okay I use 20th generation as an example different cells will start to die at different Generations now the question is why there seems to be a limit to how many times a cell can undergo the mitotic cell cycle okay so it will undergo the mitotic cell cycle once twice twice continue four times five six seven until it reaches a certain generation where the cells will die off here is what is actually causing the limit for the cells to not continue undergoing mitosis that limit comes in the form of telomeres now what exactly are telomeres then telomeres are basically the ends of a chromosome made up of repeating bases and where are they located like I said it's in the end of the chromosomes they can be at the end of the chromatin where I'm highlighting it in yellow or they can also be at the end of the chromatid where I'm also highlighting it and yellow as well remember the chromatin and chromatid are actually the same except one is in their uncoiled form which is the chromatin and the chromatid is it's super coiled form so one of the important questions here is how do telomeres actually limit the mitote cell cycle so that's what we want to know in this particular video so let's look at the mitotic cell cycle again in just a little bit of revision now we always start off with a newly divided cell I'm using skin cell as an example but it can be any other cells like muscle cells neurons and such now a newly divided cell will usually undergo interfaced interface is made up of the G1 s and G2 it becomes a mutual cell ready for mitosis the mature cell will undergo the M phase where mitotic division happens the nucleus divides and then cytokinesis happens where the cell divides to produce two newly divided cells now assuming that the mitotic cell cycle happens twice let's just focus on the cells that I've highlighted okay so when the mitotic cell cycles have uh happened the newly divided cells produce more newly divided cells which produce more newly divided cells now let's just focus on the three cells that I've highlighted all right and let's look at their chromatin now if you remember each of the newly divided cells are genetically identical which means to say that the DNA in all these three cells or the chromosomes in all these three cells have to be exactly the same however when we look at these three newly divided cells in their first generation Second Generation and the third generation okay we notice something rather interesting chromatins are progressively becoming shorter and if you remember the telomere is at the end of the chromatin so the telomere is actually becoming shorter now that's about the peculiar thing that is happening isn't it right so there seems to be a loss of telomeres happening across the generations of the newly divided cells the question is why so in the mitotic cell cycle before a cell undergoes mitosis the chromatens or the chromosomes will have to undergo DNA replication in the S phase for some reasons that we do not have to delve into DNA replication does not copy the chromosomes exactly a hundred percent right now what I mean by that is every time DNA replication happens the DNA is not replicated perfectly until the very end the reason is because of the functions of DNA polymerase I'm not going to elaborate on this okay but because of the imperfections in DNA replication there will always be a little bit of DNA that is lost every time DNA replication occurs and every time this DNA is lost it leads to the loss of telomeres right and I'm just throwing it in a line as you can see here after DNA replication occurs the replicated chromosomes are just slightly shorter and when they're just slightly shorter that is the loss of telomeres that is happening over that so the question here is are there any consequences when there is the loss of telomeres yep there is a consequence to the loss of telomeres now how let's imagine a cell in its first generation okay the first generation of cell or the parallel cell and the cell has its chromatin uh I'm just drawing out the chromatin and the highlighted Parts represent the telomeres now I'm also going to highlight some green Parts over there and those green parts are actually genes okay and that's a gene now let's assume that a gene the gene actually controls the function of the cell it allows the cell to produce specific proteins right and this Gene let's say it allows the cell to produce ATP which is an important energy molecule that the cell needs this particular Gene highlighted in green color at the top there it allows the cell to produce ATP all right so it's an important part of the DNA when the cell produces the second generation and repeat the process to the third generation the fourth and so all for example until the 15th generation let's see what happens to the telomeres the telomeres progressively become shorter now in the first second and third generation you notice that the telomeres are still intact even though they're progressively becoming shorter but in the 15th generation what has happened is the telomere is gone and when the telomere is gone the loss of DNA has now overflowed into the gene okay so what do I mean by that is in the first second and third generation the gene is fine okay but in the 15th generation the gene is lost partially is this a bad thing yes it is because remember I told you that that Gene was to allow the cell to produce ATP so the first generation the gene is intact so the cell is able to produce ATP second generation the gene is fine it can still produce ATP the third generation genus still intact yep it still can but in the 15th generation because the gene is lost it cannot produce ATP anymore so the cell function is disrupted in this case it's unable to produce the energy molecule required all right and because the gene is lost and the cell function is disrupted guess what happens to the cell well you guessed correctly the cell dies that is the limit that is why specialized cells such as skin cells only a lot that was a mouthful they cannot undergo mitosis forever or they cannot undergo the mitotic cell cycle an infinite amount of times it is impossible due to the constant or due to the progressive loss of the telomeres if the telomeres are lost a little bit it's fine as as we can see in the first second and third generation but once all the telomeres are gone the loss Will spill over or the genes will start to be lost as well and therefore it will disrupt the function of the cell or it disturbs the function of the cell and the cell dies off so the telomeres prevent any loss of actual genes until the telomeres run out and once the telomeres run out then the actual genes are lost in the DNA and the cell will die so if I wanted to visualize it as chromatids instead instead of drawing it as chromatins I'm visualizing it as chromatids okay so you can see the label diagram over here you can see that every time DNA replication every time the cell divides the telomere is slowly becoming shorter for the first second and third generation the genes are still fine but in the 15th generation the telomeres are completely gone to a point where it leads to the loss of genes so this is just visualizing the chromosomes but in the chromatid form they are super coiled form there's a just another way of just visualizing chromosomes and the loss of telomias so in summary what exactly happens is telomeres are just DNA at the end of the chromosomes whether they are in the chromatin or chromatid forms I'm highlighting it in yellow again they gradually shorten as the cell goes through mitotic cell division okay now so as the cell continues to divide as you can see here the telomeres are becoming shorter but the cell is still alive because the genes are not damaged yet or the genes are not lost as I'm highlighting it in the green color now but if the cell continues to undergo cell division the telomeres will eventually be lost and when the telomeres are gone the actual genes are also going to be lost within the cell the cell is unable to continue on its normal functions uh there are the metabolism within the cell or chemical reactions within the cell will be disrupted or disturbed and therefore the cell dies this is how telomeres prevent or the telomeres limit the mitotic cell cycle in a lot of cells

in one of the earlier videos we were looking at the structure of the chromosome and we noticed that the chromosome has a few different structures they have the centromere telomeres and the genes so in that previous video I said that we&#39;ll be talking about the telomere in a later time that time has now come now before we talk about telomeres in detail we want to start ourselves with a simple situation okay and this is a question that I love to ask my students now imagine if you took a skin cell out of a person&#39;s body right and a skin cell is a very interesting cell that can undergo mitosis if it wants to if you stimulate it to undergo mitosis now if you were to put the skin cell in a petri dish and you were to stimulate the skin cell to undergo mitosis you gave it all the nutrients and substances it requires the cell will undergo mitotic cell cycle repeatedly okay so just basically undergoes mitosis from one skin cell it produces two four eight and it just keeps going on now but the question is does it go on forever and does it just continue undergoing mitosis now some of my students say yes but my other students will say no because they will run out of nutrients in the battery dish which is a pretty good answer all right but then I&#39;ll ask my students another question where I say assume that the nutrients were not a limiting factor so we assume that the nutrients were constantly that there was sufficient nutrient for all the cells will the cell then continue to undergo mitosis until you have a colony of skin cells growing like a monster covering the floor is this basically glowing mitosis and it&#39;s just the colony of skin cells is becoming larger and larger and larger until it covers the entire Earth well the thing is it doesn&#39;t because assuming that a cell we start off with the cell as the first generation and every time it undergoes mitosis it becomes the second generation so third generation so on and so forth um when this cell especially a skin cell reaches for example the 20th Generation all right the cell will just die now the cell dies not because of a lack of nutrient it just does okay I use 20th generation as an example different cells will start to die at different Generations now the question is why there seems to be a limit to how many times a cell can undergo the mitotic cell cycle okay so it will undergo the mitotic cell cycle once twice twice continue four times five six seven until it reaches a certain generation where the cells will die off here is what is actually causing the limit for the cells to not continue undergoing mitosis that limit comes in the form of telomeres now what exactly are telomeres then telomeres are basically the ends of a chromosome made up of repeating bases and where are they located like I said it&#39;s in the end of the chromosomes they can be at the end of the chromatin where I&#39;m highlighting it in yellow or they can also be at the end of the chromatid where I&#39;m also highlighting it and yellow as well remember the chromatin and chromatid are actually the same except one is in their uncoiled form which is the chromatin and the chromatid is it&#39;s super coiled form so one of the important questions here is how do telomeres actually limit the mitote cell cycle so that&#39;s what we want to know in this particular video so let&#39;s look at the mitotic cell cycle again in just a little bit of revision now we always start off with a newly divided cell I&#39;m using skin cell as an example but it can be any other cells like muscle cells neurons and such now a newly divided cell will usually undergo interfaced interface is made up of the G1 s and G2 it becomes a mutual cell ready for mitosis the mature cell will undergo the M phase where mitotic division happens the nucleus divides and then cytokinesis happens where the cell divides to produce two newly divided cells now assuming that the mitotic cell cycle happens twice let&#39;s just focus on the cells that I&#39;ve highlighted okay so when the mitotic cell cycles have uh happened the newly divided cells produce more newly divided cells which produce more newly divided cells now let&#39;s just focus on the three cells that I&#39;ve highlighted all right and let&#39;s look at their chromatin now if you remember each of the newly divided cells are genetically identical which means to say that the DNA in all these three cells or the chromosomes in all these three cells have to be exactly the same however when we look at these three newly divided cells in their first generation Second Generation and the third generation okay we notice something rather interesting chromatins are progressively becoming shorter and if you remember the telomere is at the end of the chromatin so the telomere is actually becoming shorter now that&#39;s about the peculiar thing that is happening isn&#39;t it right so there seems to be a loss of telomeres happening across the generations of the newly divided cells the question is why so in the mitotic cell cycle before a cell undergoes mitosis the chromatens or the chromosomes will have to undergo DNA replication in the S phase for some reasons that we do not have to delve into DNA replication does not copy the chromosomes exactly a hundred percent right now what I mean by that is every time DNA replication happens the DNA is not replicated perfectly until the very end the reason is because of the functions of DNA polymerase I&#39;m not going to elaborate on this okay but because of the imperfections in DNA replication there will always be a little bit of DNA that is lost every time DNA replication occurs and every time this DNA is lost it leads to the loss of telomeres right and I&#39;m just throwing it in a line as you can see here after DNA replication occurs the replicated chromosomes are just slightly shorter and when they&#39;re just slightly shorter that is the loss of telomeres that is happening over that so the question here is are there any consequences when there is the loss of telomeres yep there is a consequence to the loss of telomeres now how let&#39;s imagine a cell in its first generation okay the first generation of cell or the parallel cell and the cell has its chromatin uh I&#39;m just drawing out the chromatin and the highlighted Parts represent the telomeres now I&#39;m also going to highlight some green Parts over there and those green parts are actually genes okay and that&#39;s a gene now let&#39;s assume that a gene the gene actually controls the function of the cell it allows the cell to produce specific proteins right and this Gene let&#39;s say it allows the cell to produce ATP which is an important energy molecule that the cell needs this particular Gene highlighted in green color at the top there it allows the cell to produce ATP all right so it&#39;s an important part of the DNA when the cell produces the second generation and repeat the process to the third generation the fourth and so all for example until the 15th generation let&#39;s see what happens to the telomeres the telomeres progressively become shorter now in the first second and third generation you notice that the telomeres are still intact even though they&#39;re progressively becoming shorter but in the 15th generation what has happened is the telomere is gone and when the telomere is gone the loss of DNA has now overflowed into the gene okay so what do I mean by that is in the first second and third generation the gene is fine okay but in the 15th generation the gene is lost partially is this a bad thing yes it is because remember I told you that that Gene was to allow the cell to produce ATP so the first generation the gene is intact so the cell is able to produce ATP second generation the gene is fine it can still produce ATP the third generation genus still intact yep it still can but in the 15th generation because the gene is lost it cannot produce ATP anymore so the cell function is disrupted in this case it&#39;s unable to produce the energy molecule required all right and because the gene is lost and the cell function is disrupted guess what happens to the cell well you guessed correctly the cell dies that is the limit that is why specialized cells such as skin cells only a lot that was a mouthful they cannot undergo mitosis forever or they cannot undergo the mitotic cell cycle an infinite amount of times it is impossible due to the constant or due to the progressive loss of the telomeres if the telomeres are lost a little bit it&#39;s fine as as we can see in the first second and third generation but once all the telomeres are gone the loss Will spill over or the genes will start to be lost as well and therefore it will disrupt the function of the cell or it disturbs the function of the cell and the cell dies off so the telomeres prevent any loss of actual genes until the telomeres run out and once the telomeres run out then the actual genes are lost in the DNA and the cell will die so if I wanted to visualize it as chromatids instead instead of drawing it as chromatins I&#39;m visualizing it as chromatids okay so you can see the label diagram over here you can see that every time DNA replication every time the cell divides the telomere is slowly becoming shorter for the first second and third generation the genes are still fine but in the 15th generation the telomeres are completely gone to a point where it leads to the loss of genes so this is just visualizing the chromosomes but in the chromatid form they are super coiled form there&#39;s a just another way of just visualizing chromosomes and the loss of telomias so in summary what exactly happens is telomeres are just DNA at the end of the chromosomes whether they are in the chromatin or chromatid forms I&#39;m highlighting it in yellow again they gradually shorten as the cell goes through mitotic cell division okay now so as the cell continues to divide as you can see here the telomeres are becoming shorter but the cell is still alive because the genes are not damaged yet or the genes are not lost as I&#39;m highlighting it in the green color now but if the cell continues to undergo cell division the telomeres will eventually be lost and when the telomeres are gone the actual genes are also going to be lost within the cell the cell is unable to continue on its normal functions uh there are the metabolism within the cell or chemical reactions within the cell will be disrupted or disturbed and therefore the cell dies this is how telomeres prevent or the telomeres limit the mitotic cell cycle in a lot of cells

Transcript for:Understanding Telomeres and Cell Division

Transcript for:
Understanding Telomeres and Cell Division