Control of Cell Size

Hi in this video we're gonna be talking about control of cell size. So first let's talk about the extra cellular factors. So there are three extra cellular factors that play a role in the cell division cell size and cell survival and all of these things. Right? I know I mentioned size but division and survival also relate back to size right? Because in order to divide the cell has to be larger in order to survive it can't be too small. So all of these factors play a role in making sure the cell is the right size. So mid regions are extra cellular factors that stimulate cell division and they do this by removing negative control. So things that are going to block the cell cycle progression. So they remove these inhibitors of cell cycle. Um And usually they do this through G. One and S. One C. D. K. S. So my question is super important right? Because if they're stimulating cell division and they're stimulating cells to grow then you have the growth factors. And these are really responsible for stimulating cell growth sort of independent of anything else. Um Because they promote protein synthesis. So if you're creating more proteins then you're gonna have more proteins. You're gonna have more organelles, you're gonna have more proteins in the membrane, it's gonna have to keep growing and growing and growing. Um And if you also works by inhibiting degradation. So not only creating more proteins but you're not degrading them as fast. And so growth factors really stimulate cell growth um like independent of other things like division or survival or whatever and then finally you have survival factors and these are gonna stimulate cell survival and they do this by suppressing apoptosis which if you remember what apoptosis is that's just regulated cell death and we'll go over that a lot more in another video. But so those are the three factors that really control um cell survival, growth and division. But it's super important to understand the difference between each three and not confuse them. So you're like okay well they're all you know pretty much stimulating the same thing but they're not because each one is activating a specific way. So my surgeons are removing these inhibitors of cell cycle growth factors are promoting protein synthesis and survival factors are suppressing or blocking regulated cell death. And so um when we talk about cell growth, it's also really important to understand that doesn't mean cell proliferation. So what does cell proliferation mean? Right, so that's gonna be cells dividing a lot. So there's going to be many cells like to start if you start out with two cells and after an hour you end up with 32, that's a lot of cell proliferation. But cell growth is actually referring to one cell and its size. So that is a super important differentiation. So here's how a growth factor stimulated cell growth. So here's a growth factor, it binds to some kind of something in the plasma membrane which stimulates a variety of different proteins sort of downstream which will trigger the cells to grow and all of these doctors work very similarly. But this is just an example. So when the sound needs to grow these growth factors bind and they stimulated a variety of intracellular proteins. So let's talk about a few of these intracellular proteins that control cell size in the cell cycle. So um mid regions like I said before really worked by stimulating these G one C. D. K. S that enter the cell into the growth phase of the cell cycle. So if my pigeons weren't present during the cell cycle then what would happen is the cell would enter G zero and it would pretty much stay there. So without my pigeons the cells aren't gonna grow and they're not going to divide. So um mid engines work by activating these intracellular G one C. D. Ks. A second pathway is through the E two F transcription factor. And so um this is activated by mid regions. It's activated by growth factors. Um here's a couple of examples. You don't necessarily need to know those but if you just see them in your book, that's what they are. And so E two F transcription factor. So it's obviously doing something to transcribe genes and so the genes that it is activating are promoting actually entry into s phase. So that's a super important one. Right? Because when the cell has finally reached size it doesn't need to keep growing, it needs to stop growing and it needs to move on through the cell cycle. And so the E. Two F. Transcription factor is super important to kind of recognize when the cell has actually gotten to its size and promoting that movement to the next step. Um You're actually going to probably be hearing a lot about this pathway. Um And I'm just going to briefly mention this and I'll show you an image later. But this transcription factor is inhibited by this special protein called the retinoblastoma protein. And the reason I'm telling you this about this protein is one because you're going to see it a lot in your book and you need to know what it does. But two is because this protein is actually mutated and a lot of cancers and you can imagine right because if it if if this protein is responsible for inhibiting movement through the cell cycle and stopping cell growth then if it's mutated and it doesn't work then the transcription factor is going to just you know, go through the cell cycle as many times as it wants, even if the cell isn't running. So that's a really important one. Especially in cancer. Then you have the wrasse map K signaling pathway which we've talked about previously a little while back and this works very similar. It activates transcription factors that support growth. And then finally the DNA damage repair pathway. Um And this pathway can also pause the cell cycle um and result in cell growth while the cell is trying to repair its D. N. A. And this pathway which we've talked about before is the P. I. Three K. K. Katie pathway of signaling. So here's this example that I said I was going to talk about which is the E. Two F. And the retinoblastoma. So here we have some type of cycling and some type of C. D. K. Which are working together and they're like hey we want to promote the sale cycle. So what they do is they actually promote E. Two F. And so when E to F is now activated and it's ready to go, it will promote the sale cycle. But when our B. Comes in and binds to it, this causes inhibition and blocks the cell cycle. So the cell cycle is now blocked. So you can imagine that if this protein which is regulating this one is mutated. So the R. B. Is mutated, then this E. To F. Is just free to promote the cell cycle and promote cell division and cell growth just whenever it wants to. Without inhibition, which you can very easily see how this results in cancer. So with that let's now turn the page

Which of the following factors is not responsible for controlling cell division, size, or survival?

• A. Growth factors
• B. Survival factors
• C. Integrins
• D. Mitogens

Which of the following proteins is a transcription factor that activates genes to promote entrance into S phase?

• A. Mitogens
• B. RAS-MAPK
• C. PI3K-AKT
• D. E2F