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Mitosis vs Meiosis Basics · Acedra
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Mitosis vs Meiosis Basics
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0:02
in previous lecture we had discussed that sperm and zygote not zygote sperm and ovum they fused to form a single cell card zygote and this lie code has the potential to form a complete organism with multi trillion cells right now the sperm and ovum they consist of how much chromosomes 23 chromosome 23 chromosome sperm and 23 chromosomes from ovum and then when they combine they form zygote that consists of 46 chromosomes and from zygote the widths from zygote with cell division 1 to 2 2
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to 4 4 to 8 and so on many different cells formed until a complete organism is formed and each cell each cell of a human being consists of 46 chromosomes so what I mean by this is that a chromosome numbers remained same from zygote onward the chromosome number remains same that is 46 so from zygote the cell division that leads to formation of same number of chromosome that is called mitosis right and the cell division that leads to formation of sperm and ovum is called
1:36
meiosis and in meiosis chromosome number of chromosome number is decreased right the cell from which these gametes male and female gametes they are formed that cell consists of 46 chromosomes but these gametes consists of 23 chromosomes 1/2 number of chromosomes it but from zygote onwards whatever the cell division that leads to formation of cells that consist of same number of chromosome and this type of cell division is called mitosis the two types of cell division
2:16
are there two types of cell divisions are they there one is mitosis that occurs in somatic cell all of the bodily cells right and meiosis it occurs online gametes the sex cells right the first we will discuss mitosis usually in embryology we go in chronological order so ideally we should have discussed meiosis first but we are first discussing mitosis because it will be very easy for us to understand meiosis and we will first understand mitosis
2:57
so mitosis consists of two parts we can discuss mitosis under two levels that is division of DNA or nucleus and division of cytoplasm organelles and cell membrane this this part is called cytokinesis the named part is division of nucleus and it is the toughest part relatively tough part to understand so our main focus of understanding is division of nucleus but let me tell you something about the DNA you know what is the length of DNA yes it's something that from Earth to
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Mercury and then returned back yeah the DNA is so long but that is DNA of all the cells of our body right the DNA of single cell is about one point eight meter long DNA length of DNA of a single cell is about 1.8 meter what is the size of an average human cell that is 40 to 50 micrometer so much small-cell and such a long DNA is paired inside not only that's so much small cell but a part of that cell it is packed inside nucleus of that very small cell so how it is packed inside how DNA
4:30
is packed inside thus the nucleus of a cell let's see how so here is the DNA it consists of nucleotide bases right the code of our all the proteins of our body that is present inside the DNA right and it is in the form of nucleotide sequence so this is the nucleotide sequence and you know we have double-stranded DNA this double-stranded DNA is quite around each other to form a double helical structure double helical structure is there right
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then this double helical DNA it interacts with histone proteins histones are positively child protein they are positively charged because they have abundant amount of their large amount of basic amino acids and what is the charge of DNA it is positively charged or negatively charged on neutral it is negatively charged yes because of phosphate groups phosphate groups are present which imparts negatively negative charge to DNA and this negatively charged DNA it interacts with
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positively charged histone proteins you know if we have four we have four histone proteins that form an octamer and this DNA it is woven around this October histone octamer DNA is woven around histone octamer and this structure this stone complex with DNA around it it is now called nucleus home this nucleus home complex is then further coiled around each other around itself to form the structure that is called chromatin it is called chromatin right then this chromatin is further
6:36
bound around each other to form a three-dimensional geometry called chromatid so what is chromatid chromatid consists of chromatin that is further coiled around each other and here's certain proteins that hold up into the structure these proteins are called scaffolding proteins and it forms this beautiful three-dimensional structure and this three-dimensional structure is called what chroma chromatid so this is a structure of whole chromatid and here this part is called centromere yes you
7:18
have a question if this is chromatid then what is chromosome oh we will discuss what is chromosome later if I tell you right now you will be confused so I will discuss that later
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so here is a cell and in the nucleus of cell DNA is present in the form of vomiting it is present in the form of chromatin and that is before the division start that is before mitosis start when mitosis start it is further tacked up in the form of chromatid firstly it was in the form of chromatin lose nearing it but then when cell division start it is packed up in the form of chromatids that is just like when you have to carry some baggage some luggage from one place to another
8:16
you have to further pack it up you cannot take it away in in loosely Iranian fashion you have to pack it up in briefcase or something right so that's why it is further paired up so that it is it becomes easier to divide it so this failed this first phase of mitosis in which DNA is further condensed it is further paired up this is called prophase P for parent P for prophase easy similarly in this phase nuclear membrane starts to disappear in C nuclear membrane start to disappear so
8:59
that division of DNA becomes much easier now here let me tell you something now you see we have actually 46 chromatids we have 46 double helical DNA molecules in each cell we have 46 double helical DNA molecules arraigned in the form of chromatids right now but I have only shown here four and it is representing 46 from chromatids no I have a question that let's suppose if we divide these chromatids that half goes to one cell and the other half goes to other cell
9:42
now each cell will have half number of chromatids each cell will have half number of nuclear material each cell will have half number of DNA this should not happen in mitosis right that's not how mitosis should occur how can we solve solve this problem actually before prophase start before mitosis start there is an other phase in which cell prepares itself for mitosis that is called interphase and in interphase this chromatids they replicate a copy of this chromatid is
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formed in front of it so that it can be easily divided so now I am talking about inter fail before mitosis start in the interphase this DNA exact copy of this DNA is formed in front of it by the process of DNA replication and this DNA copies again but they're quite interacts with histones and coiled to form chromatin so now we have a copy of chromatin right and this copy of chromatin in prophase again it is condensed to form two sister chromatids two chromatids that are
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exactly same as the previous one they are exactly alike and because they are exactly alike they are exactly same we call them sister chromatids I know you don't exactly resemble your sister but for the DNA for the chromatid their sister resembles each other right things are different at molecular level so two sister chromatids they are attacked with each other at this part that is called centromere and this whole structure it is called chromosome so this is actually chromosome so actually
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in prophase we have two sister chromatids not just one and these chromatin these two sister chromatids they are paired together to form a chromosome and this is prophase remember DNA is not replicated in prophase DNA is replicated even before prophase start in interface specifically S phase synthesis phase of interphase we are not discussing interphase so I am NOT going to tell you the details of interface but chromatin is copied DNA is copied in interphase and then it is further
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condensed to form to form chromosome in prophase right let's move forward
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no in this phase chromosome chromosomes are arrayed on midline they are arrayed on to equator on to midline and they form a plate like structure and this this thing is called mitotic metaphase plate this is called metaphase plate right so this phase in which chromosomes are retained on midline it is called metaphase and for midline em for metaphase easy then there are special organelles called centrosomes and razones and from centrosomes special fibers originate fibrous structure
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originated and they attach to chromosome at this part at centrosome no.not centrosome at centromere they attach these spindle fibers attach at center of mirror and not exactly at the centromere but it is a part of centromere that's well this is a part of this is the centromere and here these fibers are hooked to get hooked with a special protein here with this protein and this protein is called kinda dope or they are hooked with kinetochore why it is called kinetochore by nato means to
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move and core means chromatids this kinetochore it helps to move the chromatid away from each other it helps to move the chromatid away from each other so it is called kinetochore and these fibers which attach to centromere add kinetic or they are called kinetic or fibers they are called kinetic over fibers then there are at the fibers that are not attached with Kinetico and they are called no one can I talk about fibers are they're also called polar fibers older fibers and both of these are
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spindle fibers easy now what happens these fibers these kinetochore fibers they shorten in length their length decreases and when they shorten they will pull from this hook from this kinetochore they will pull these chromatids away from each other from this point they will pull it away from each other here also they will pull it away from each other right and these non kinetochore fibrils are polar fiber their length increases they elongate they elongate the lengthen up
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and kinetochore fibers they shortened due to lengthening of non-kyoto core fibers cell also elongate right let's see what happens so that's exactly what happened these fibers shorten pulling the chromatids away from each other and these non kinetochore fibers they lengthen along getting the cell this phase is called end of phase and in this phase chromatids move away from each other a far away a for nFA's but this is happening in anaphase easy they are moving away from each other
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finally with a splendid hard work of the spindle fibers these chromatids ultimately reach their destination they reach far away from each other these sisters are now separated and this happens in telophase chromatids are now far away they can only see each other with any scopes these sisters can only see each other with telescope of course they do not have some molecular telescopes inside the cell but that is just a mnemonic so that you will remember don't tell anyone that they are carrying the
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telescope inside the cell
17:30
the nuclear membrane also reappears and that is about the telophase the last phase of nuclear part of nuclear division of mitosis next we will discuss what title kinase is division of site of large organelles and plasma membrane
17:57
so in cytokinesis there is formation of special contractile ring in the cytoplasmic side of cell there is formation of contractile ring it is it consists of actin myosin proteins I am NOT going to go into detail and due to this there is a cleavage furrow is formed a pit or groove is formed here right and which will ultimately lead to division of site applause organelles and plasma membrane into two and we will ultimately lead form two daughter cells from one cell
18:41
ultimately now we have two daughter cells and each daughter cell F equal number of DNA of course they have chromatids but before next mitosis start in the interphase they will form another chromatid in front of it to form a complete chromosome so now you know what is the difference between chromatid and chromosome and what is the concept of sister chromatids lirikten law so now I will not speak now you will just watch the complete animation of mitosis
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you
19:40
so this was mitosis very easy let's review again in first phase prophase DNA is packed into chromatids and in metaphase it is arraigned on chromosomes are retained on midline in anaphase they move away from each other the starts to move away from each other and telophase they are now far away from each other looking at their sisters with special telescopes right and ultimately in cytokinesis they separate out yes you have a question yes with each cycle of mitosis the number of organelles are
20:23
also reduced to half then what happens in the subsequent degree and then organelles will be there next door but the organelle is will not vanish actually in interphase not only DNA is replicated but organelles are also copied they are also replicated so that we have a copy usually more than one copies of organelle each organelle so that with the cell division the organelle is are distributed equally to daughter cells right so it in interphase many different things occur there are
21:01
different phases of that we will not discuss the detail actually DNA is replicated right organelles are replicated and cell prepares itself for cell division for mitosis right another question do you think spindle fibers they form in metaphase or which phase yes metaphase no actually spindle fibers they start to form in prophase but they attaches with kinetochore and they they they complete they undergo the complete synthesis in metaphase the spindle fibers start to form in prophase clear
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so this was about mitosis if you liked this video please give it a thumbs up please share your comments regarding this we please subscribe to my channel and please support me on patreon thank you
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