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Video transcript

let's talk a little bit about the lifecycle of a cell in particular we're going to talk about interface the interface part of the lifecycle of a cell and as we'll see interphase is where a cell spends most of its life let's draw a timeline for a cell so let's say this is a this is a I guess you could say a new cell and it will go through interphase so I'm going to make it like a cycle so it's going to go back on itself and at some point so all of that is interphase at some point it will be ready to divide and it will undergo mitosis and mitosis is more formally it's the process by which the nucleus turns into two nuclei but then that's obviously needed for cell division so this is mitosis right here in green so as you see and this isn't precise a cell spends most of its life and interphase and that's where it's just you kind of living as a cell it's living growing producing proteins whatever other functions it has and mitosis it's a shorter part of its life a smaller fraction a very interesting part it's a necessary in order for the cell to replicate but you see it's a much smaller fraction but what I want to focus on in this video is interphase and to do that let's draw ourselves a cell so let me copy and paste so this right over here actually let me I did that just to save time so let's say this is a cell so in green I have its nuclear member or not the nuclear where I have its cell membrane inside of that of course you have all of the you have all of the cytosol and then in this in this orangish color I have the nuclear membrane that defines the nucleus and then inside of that I have the DNA and you might be used to seeing DNA all tightly bound or chromosomes all tightly bound like that and like that this or like this this would be another chromosome right over here in magenta but during interphase the chromosomes aren't tightly bound like that so that they're easy to see from a traditional or a simple light microscope for most of us cells lives the chromosomes are completely unwound they are in their chromatin form so they are in their chromatin for it's actually hard to see if you have just a simple microphone simple microscope it's all unwound you just have the proteins and the DNA it's all tangled together now there's one other thing that I drew here and this is you might say why am i drawing it when I haven't drawn most of the other organelles but I'm drawing this thing which is called a centrosome because it's going to be it's going to be important for it's going to be important when we go into my ptosis now this drawing is well you might say anybody doesn't does it to sell at least a human cell kind of a the diplom that has a diploid number of chromosomes and once again if we're not talking about sex cells and we're talking about just our somatic cells doesn't have 46 chromosomes it looks like you only drew two and it is true I only drew two chromosomes for the sake of simplicity we're just going to assume this is the cell of some organism that's much simpler then it only has two chromosomes so anyway this is the new cell right over here and it is going to grow so it is going to grow it's going to take in nutrients from its environment and it's going to grow as we would expect it to so that's that right over there and then let me give it its nucleus and it's centrosome just like that and this phase this phase where it is just growing from this new cell this is this phase right over here is the g1 phase the G want actually let me do that in a different color since I'm already using that green so much this is the g1 phase and so that might look something like this different cells are going to do this for different periods of time the g1 phase but then you can imagine well look it's going to need to replicate some of the info or it's going to replicate the information inside of the the or that's that's coded by the DNA at some point and actually this happens before mitosis and so let's depict that so let me draw let me draw the nucleus and the centrosome again so let me draw that again and let me draw the cellular membrane this nice healthy growing sell and now it's DNA is actually going to replicate so instead of having one copy of of its DNA it's essentially going to go to two copies but I want to be very very careful now so if I draw that magenta chromosome up here so once again it's all unwound like that when it replicates it's going to create a copy of its DNA and once again I'm not doing justice for how much DNA how much DNA there actually is but it was one chromosome before it was one chromosome when it was just like this and it's still one chromosome even though it's copied its genetic material let me draw this a little bit neater so this is one chromosome right over here and that one chromosome after it's copied all of its genetic material it is still one chromosome now how do we how do you know but there's two copies over here what do we call these two copies well each of these two copies are called a chromatid and these two right over here these are sister chromatids sister sister chromatids but either way this is one chromosome right over here chromosome chromosome and this is also so this is one chromosome right over there and that is also one chromosome this whole thing right over here is also one chromosome later on when we go through mitosis will see that these two sister chromatids get split apart they're no longer connected and at that point we refer to each of them as a individual chromosome now you might be wondering is there a word for this place where these two sister chromatids are connected and the answer is yes there is a word and that word is centromere not to be confused with centrosomes so let me give myself some space here so that right over here that is a Centro Centro vir right over that so we had one magenta core with this we had this magenta chromosome right over here and now it replicates it's still one chromosome although it has twice the genetic material right now you have these two sister chromatids connected at the say the centromeres right over there and that's also going to happen for the blue chromosome all this genetic material is going to replicate you're gonna have two copies of it and so now it's going to be made up of two sister chromatids that are maybe connected once again at at a centromere and also while all of this replication is happening inside the nucleus the centrosome also duplicates the centrosome also also duplicates and this process the part of the life cycle where all of this genetic information is duplicating we call that the S phase S phase for synthesis so this is the synthesis phase so that is the S phase and then before going into mitosis there is one more growth phase there's one more growth phase and we call that g2 so we have one more growth phase which we call g2 and then we are ready so let me just copy and paste this actually let me just do this so that's what we had before now we need to remember that our DNA has replicated so our DNA is replicated so let me draw that like that let me draw the two centromeres for one for each of the chromosomes let me draw the center the replicated the duplicated central zome I thought to be confused with centromere and now the cell has grown even more the cell has grown the cell has grown even more and once again going from this to this we call that the g2 phase and at this point at the end of the g2 phase this is now when we are ready this is now let me do this in a different color this is now when we are ready for mitosis
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