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Video transcript

we have other videos where we talk about how small molecules or ions might be able to go through a cell's membrane in different ways whether actively or passively may be facilitated in some way what we want to talk about in this video is how we can do this for larger things so we're going to focus on here is bulk bulk transport transport so this first example you could imagine this this cell with this move or purple colored membrane is engulfing this big green thing which is maybe a bacteria or something and so you see that the membrane let me make it very clear this is this is inside this is inside the cell this is outside outside the cell and you can see the cellular membrane starts to wrap around this I guess we can think of this as a bacteria it then it fully wraps around and then that membrane that was wrapping around the bacteria pinches off and now the bacteria is inside of the cell and it's wrapped by this membrane and this process where you're engulfing these large things we call this phagocytosis so this is phago Saigo cytosis and the prefix i guess you could say phago comes from the greek for to eat so this is literally about cell eating and in many cases this thing that is now in here you could view this as the cells food this compartment that is holding this this this in this case bacteria is going to transport it maybe to a lysosome so it can be processed and digested in some way we would call this big compartment this membrane bound compartment we would call this a food vacuole food food vacuole now this scenario down here is similar but but different over here I have the cell which is I see part of its membrane and it's in magenta right over here we could see the phospholipid bilayer that's what I drew what that's why I drew two lines for the membrane and instead of engulfing a large particle or bacteria it's just engulfing some fluid it's engulfing some fluid so you see it's starting to wrap around this section of fluid wraps even more around the section of fluid then the membrane that was around it completely pinches off and goes into the cell and I'm drawing all of these things in two dimensions but this was actually be happening in three dimensions so this wouldn't just be circle this we right over here would be a sphere and this thing that has been pinched off and is now inside the cell we call this a vesicle which is it just a general term for these membrane-bound compartments inside of cells and this process where the cell has essentially drunk a bunch of fluid and the stuff that happens to be in the fluid we call this pinocytosis pinocytosis pinocytosis and Pino comes from the Greek word to drink and I'm always fascinated by word roots and I'm not a linguistic expert here but it's neat because even in languages I'm familiar with like Hindi and Urdu they the word Pina means to drink so it's and maybe it's even related to the word pani which is in those words in those languages I know all of these have a shared linguistic root so it's always fascinating to see these to see these linguistic connections so this is pinocytosis where you're the cell is drinking so to speak but it's also getting the other stuff that's in that fluid this is phagocytosis the cell is eating and those these are both special cases of I guess the more general term of engulfing in this way which is called endocytosis endo endo Tsai ptosis so phagocytosis is a form of endocytosis and pinocytosis is a form of endocytosis now the next question you might say is okay I can get that this happens this can be observed under a microscope but how does it happen how does the cell wrap around and pinch around and like I say in a lot of videos people think that we understand some of it but this is not fully fully understood there's views that well the cytoskeleton the cytoskeleton must be involved in some way it has to create it has to create space here for for this thing to be able to for this thing to be able to pinch off and move in that direction it maybe will help actually the the cell the cell's membrane wrap around in some way but these are all areas of active research how does this endocytosis actually occur how does the cell know what what - endo site at what - to consume I guess you could say and then how does the membrane actually behave in this way to do it to do it well
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