Interphase

so now that we briefly introduced the cell cycle in our previous listen videos in this video, we're going to begin to discuss the first major phase of the cell cycle, which is interphase and so recall from our previous lesson videos that interphase is a non dividing stage where the cell is not going to be dividing. Instead. Interphase is a stage of cell growth and organo, an enzyme production in preparation for cell division and so interphase typically makes up the vast majority of the cell cycle. And that's because interphase takes quite a long time with respect to the M phase, which is a relatively short period of time because it's a relatively fast process, the dividing phase occurs relatively quickly in comparison to interphase, which takes a long time on so once again in this video, we're focusing mainly on inter phase the phase that makes up the majority of the cell cycle. It takes a long time and so recall from our previous lesson videos that within interphase there are smaller sub phases within, and so the sub phases of interphase um, include four sub phases, and these four sub phases are based on specific events that occur inside of the cell. And so the very first sub phase here we have is G one and G one is the G here stands for growth, and this is because in the G one sub phase of interphase, the cell is going to be performing. It's normal functions, and so if it's a heart cell, it's going to be doing whatever Hartsell does. If it's a liver cell, it's going to be doing whatever liver cell does and so on. And so, in the G one sub phase of interphase, the cell is going to be performing. It's normal functions. In addition, it's also going to be growing and producing organelles, enzymes and proteins. And so when you take a look at the image down below, uh, here, uh, you'll find the G one phase. And so, really, this is where the cell cycle begins is right here at this position, and so you can see this would be a cell that Hiss first born and this cell that his firstborn is going to enter interphase. The G one phase, which is, uh, cell growth cells Gonna be doing what it normally does, and it's going to be growing and producing enzymes and organelles, then noticed that after the G one phase we're actually going to skip over the G zero phase here for now. And we're gonna transition straight from the G one over into this phase here, which is the S phase. And so the S phase, which we have is the second phase Here is, uh, the S is, uh, symbolic for the S and synthesis. And so this represents DNA synthesis or DNA replication. And that's exactly what the S phase is characterized by. The DNA is going to be synthesized or replicated, producing a replicated chromosome with two sister chromatic IDs. And so, just as we discussed in our previous lesson videos And so in addition to the DNA being synthesized or replicated in the S phase, there's another cytoplasmic protein called the Central Zone Not to be confused with the Centrum ear of, or the waste position of a chromosome of a replicated chromosome. The central zone is a cytoplasmic protein that we'll get to talk mawr about its function as we move forward in our course. But the centrism is going to be important for the M phase for my toes is later down the line. And so the centrism is going to get replicated during the S phase as well. So it's also replicated during the S phase in addition to the DNA. And so what you'll notice is in this image of the S phase, you can see it's characterized mainly by DNA replication. But in addition to DNA replication, a structure called the central zone is also going to be replicated. And in this image again, we're going to talk more about the central zone later. In our course with centrism is this structure that you see right here it's going to get replicated. And so you'll see, at the end of the S phase, there are two of these central zones and also noticed that the unrepresented chromosomes have been changed to replicated chromosomes over here in the nucleus after the S phase DNA replication. And so, after the s phase, uh, what the next phases is the G two phase. And so the G two is the third phase here, and G to also stands for growth. And really, it's just a continuation of G one in a way, because the cell is going to continue to grow and produce new proteins. And because G two is the last phase just before the M phase, Uh, the G two is also going to be, uh, preparing for the M phase. So it's gonna be creating new proteins that are required for the M phase, essentially prepping and preparing itself for the phase that follows. And so which will notice Here in this image is that at the end of the G two phase or in the G two phase, the cell is going to continue to grow. So it's character by by cell growth and also preparation for division, essentially preparing itself for the M phase and notice that the size of the cell is much, much larger than it was originally. So the cell has grown in size here at the end of interphase, and so really, uh, G two is the phase just before the M phase. And the only phase that we sub phase that we have not yet talked about is this G zero phase here, which is a not, uh, a non dividing phase where the cell is not dividing, and so essentially a cell would go from initially start in the G one phase. Um, but, um, it would Onley transition into the s phase DNA replication if the cell is going to commit to dividing. But if the cell does not want to commit to dividing, then it will not go into the S phase instead. If the cell does not want to commit to dividing, then the cell would go into the G zero phase. And so G zero sub phase is a non dividing phase where cells do not, they are not going to replicate their DNA, nor are they going to prepare for cell division. And so the G zero phase is basically a phase where cells will not divide. It will not continue through the cell cycle as normal, and some cells will be in the G zero phase, uh, for ah, permanent period of time. Whereas other cells will enter the G zero phase for a temporary period of time, and then they can also return back to the G one phase and then continue to divide. And so really, this is almost like stepping aside and saying a cell basically saying that they don't want to continue through the cell cycle just yet. They would rather remain in a non dividing stays. And so this year concludes our introduction to interphase and the sub phases of interphase, and we'll be able to get practice applying these concepts and breaking down this image here as we move forward in our course. So I'll see you all in our next video.

in this video, we're going to briefly introduce Sentras, OEMs and my topic spindles. And so recall from our last lesson video that during the S sub phase of interphase, it's characterized by DNA synthesis where the cells going to replicate their DNA. But they also replicate another structure called the central zone. And so the central zone is not to be confused with the Centrum ear, which again is the waste position of a replicated chromosome where the two Sister Crowe motives come together. The central zone is different than the central near the central zone. It is a cytoplasmic protein complex that forms or organizes what are known as the might. Ah, tick spindle on the my tonic spindle is very, very important for my toe sis, which occurs, uh, of course, during the m phase of the cell cycle. And so the my tonic spindle is really just micro tubules proteins of the site of skeleton that coordinates division of the chromosomes, essentially dividing the DNA into the two daughter cells. And so here what we're saying is that in our example images that the central zone is going to be replicated in the S phase and the central zone is ultimately going to be responsible for forming the Mitic spindle during my toe. Sis and Soe, over here in this image, down below notice. Over here on the left, we're showing you a single cell that has Onley one center zone Noticed that a single centrism actually consists of these two smaller proteins here. And so we have one single centrism right here. And we have the nucleus of the cell. Um, within the nucleus, we have these Unruh replicated, uh, chromosomes. And so notice that after the s phase, remember, the S phase is the sub phase of interphase where DNA synthesis is going to occur DNA replication. But in addition to DNA replication, the central zone is also going to be replicated. And so notice that the central zone is replicated. Now there are two centrism. There was one over here, and now there's a second centrism over here. And so we have these central zones here. But also in addition to the centrism is being replicated. Of course, the DNA is going toe also be replicated. So we convert the unrepresented chromosomes here into replicated chromosomes. Notice they each we have this thes x shaped chromosomes here indicating that they are replicated. Whereas over here they're not X shape. They are mawr linear like what you see here. And so really, that is the main point here. And ultimately these centers owns again are going to be very important during mitosis because during my toe, sis, they're going to form what are known as the my tonic spindle. And so here you can see the might attic spindle are these structures that air projecting off of the centrism and they're forming thes micro tubules that are gonna be important for ultimately moving the DNA around in splitting the division of the chromosomes dividing the chromosomes. And again, this will make the central zones and the my tonic spindle are going to be mawr relevant once we start talking about my toe sis a little bit later in our course. So this is a little bit of foreshadowing here for what you are going to see as we move forward. And so this here concludes our brief introduction to center zones and the Mitya Dick spindles, and we'll be able to get some practice as we move forward in our course. So I'll see you all in our next video