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structure and function of cell membrane
Added Oct 04, 2013
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this video we're going look at the cell membrane structure and function in fact let's start with a function and then do the structure your last video when we took a tour to the cell we briefly discuss the function of the cell membrane as a gatekeeper it's going to determine what comes in out of a cell anytime something does come in and out of cells connect the deal with this cell membrane just come look a gatekeeper it oversees all traffic in and out of our cell Factory the next function is compartmentalization by creating a distinct internal external environment sassy such as chemiosmosis and making processes such as the action potential possible we have to have a distinct outside and inside with some barrier across which things can happen and finally cell-to-cell communication and recognition when cells talk to each other signals are received by the cell membrane or hormones plug-in receptors neurotransmitters plug-in receptors during the immune system cells are recognized by the surface are proteins and carbohydrates the surface of the cell the cell membrane please very important rules in the functioning of the cell structure to some memory the fact we're going to build one in the start with these guys phospholipids you might recall from our video on biomolecules that the desert interesting molecules executive consist of a phosphate head which is hydrophilic and two fatty acid Tails which are hydrophobic so we have one another's molecule that likes water and one end it doesn't so here I have a bunch of phospholipids what would happen if I added water whippin to water molecules over here the phosphate heads are going to turn towards the water and the fatty acid tails are going to turn away well that's fine but what if I have water on both sides let's make some more water here these over here if I put some water on this side will these fatty acids are these phospholipids are going to turn and face this way do that and they're going to orient themselves like this they might self-assemble into maybe a steer and some take me awhile to get these in the right alignment but bear with me here Nepal's a Stockman jump ahead you can see that as we have water on both sides that these lipids are going to a bilayer with the phosphate head pointing out in the direction of the water and the hydrophobic fatty acid Tails pointing in and we get this bilayer double layer of phospholipids do the chemical properties of these molecules is possible if it still self-assembled is bilayer the phospholipids are the primary component of the cell membrane they're not the only components will have a variety of different proteins that are embedded throughout the membrane and serve different functions some connectors gates to allow thing travel through order channels to allow particles to move through the cell membrane can see right here others have structural components and make a bonus add some other proteins and as we go in addition to the proteins we also have carbohydrates and cholesterol does a carbohydrate sometimes we attach the proteins there can be other ones attached to our in the membrane here and we'll put some of these cholesterol Amor De Clips the cholesterol will be in the membrane here and we'll talk about what their function is also because we can see the cell membrane is a complex structure that's made of many individual pieces some would call it a mosaic additionally each of these pieces independent they're not physically connected to each other so they can move the proteins can move through the membrane that can slide back and forth d the outer layer in the inner layer can move past each other that can slide sued this Mosaic is also fluid so will you call us the fluid mosaic model of the cell membrane it's a mosaic of phospholipids proteins cholesterol carbohydrates that are fluid in nature that they can move and pass one another and we can make vesicles out of this material and I add to it so to fluid is it which system it's influx at all times she's a more artistic rendition of that model destroying you 2 Sensor 2 3 2 nature that the depth of the picture here much better than anything I can draw of course we can talk about the functions of some of these parts here the carbohydrates will listen to the Shell to sell recognition some of the markers and on the surface of cells the proteins have many functions of their involved in transport will talk more about that later helping things move in and out of the cell they maybe enzymes right there on the surface of the cell that help catalyze reactions they can help in signal transduction that can be at receptors on the surface of the cells they also could be physical markers protein markers for sale recognition and help form some of the cell to cell Junctions different rules for this proteins the cholesterol is these cholesterol is that are embedded in the membrane actually help reduce the fluidity is maybe these are trying to slide I still help the slow down that fluidity in Exeter give us a little bit more structure of the cell membrane little bit more structure talk about the properties and cell membrane we already said that it's a mosaic that's one of the properties and it's fluid that's another one that properties however the probably the most important proper is that the cell membrane is selectively permeable that means that I let some things pass through it but not others just think about this what type of party could move through the cell membrane one of the physical properties of some of that came through the cell membrane is that it's going to be small I mean physically to get through these place to make it to their you can't be Lord If This Were you no make that bigger hold on here we go this app just physically too big so one of the characteristics of a substance I can get through the cell membrane is that it must be fairly small to get through here mask just one of the properties how about this what if this particle were a Charged particle an ion it turns out that what time making it through the cell membrane even if they're small they have to find other ways in like through specific protein channels but through the Bayou player ions don't have much luck what about water turns out that water molecules can get through here even though their polar which makes most polar molecules have a difficult time but water small enough that it actually can pass through the cell membrane so we're going to make a list of things should get through this by lipid layer we say to this thing for me small non charged and non with the exception of water what does it mean that things that are larger or charged or polar can't get through they just have a hard time getting through this part do this cell by lipid layer the transports how do things get across the cell membrane well before we get into the specific types of transport we need to talk about two broad categories passive transport and active transport passive transport is transport that goes down or with the concentration gradient another words ever going down the hill which ball at the spin energy to get that ball to go down the hill if you pass it is going from areas of higher concentration to areas of lower concentration now this case I've represent as a hill but we need to think about the conservation molecules we determine whether it's passive or active transport active transport conversely is going what's the concentration gradient or up the concentration gradient to get this ball to go up the hill we have to spend energy and cells than energy and the form called MTP list of custom specific types of passive transport in the first is diffusion diffusion is the movement of materials from areas some areas of high concentration to areas of low concentration it does not cost energy is going down the hill down the hill so in this picture we look at these yellow dots whatever they may be whatever molecule these represent we see that outside of this cell there are a lot more then inside sweep a higher concentration outside than in so these yellow. Want to move which direction into the cell or out of the cell that's right they want to move in down the concentration gradient so if we were to represent this movement of these molecules in this direction would call that Fusion did you moving down their concentration gradient and grab some of these guys they diffuse across down their concentration gradient right through the lipid layer can we call that diffusion now question what if these yellow dots represent water if we what is your traps at water then this movement does diffusion of water across a selectively permeable membrane has a special name we called osmosis osmosis is the diffusion of water across a selectively permeable membrane severe specific definition and since it's diffusion it's by definition passive it's moving down the concentration gradient now what about these down here at these positive charged ions if these ions if we look at it which way do they want to move where is there a higher concentration inside outside let's free obvious to see that we have a lot more of these red positive charges insides they would like to move down their concentration gradient which this case would be out but we know that ions have difficult time getting through the by lipid layer but if there's a channel provided for them by a protein then we have a path odds to move down their concentration gradient now that being helped by a protein however it's still passive and we call it the silat ated diffusion is the diffusion of materials with the help of channel proteins it's to moving down the concentration gradient so it still pass it what about active transport can we move materials against the concentration gradient for example can we move these molecules out even though out is going up there Morgan grade answer is we can but it requires active transport let's see how this might work we have some special gate proteins here that can physically change their shape and these molecules can be moved across the membrane with the aid of these proteins now that movement is going to require the input of energy so call these guys back in here can back it up and show the input of that energy as for what might happen molecules move in an input of energy from ATP call Sister proteins again we active transport requires ATP and the help of transport proteins now what happens if the molecule or the part what trying to move in or out of the cell is this meeting on scale it's much much bigger it's obvious that this is never getting through the cell membrane it's never going to make its way through even one of these channels it's just not going to happen so can we get large particles in and out of the cell answer is yes so take the scale here and here's our large molecule and questions going to get something of this scale through this membrane and answers to endo and exocytosis yes the movement of large particles in or out of the cell getting wrapped up in a into endocytosis out of exocytosis pictures droplet falls on the surface of a cell and slowly indents further and further into the cell membrane and actually gets wrapped up and a piece of the cell membrane which we called vesicle we called this form of endocytosis pinocytosis endocytosis phagocytosis the cell moves itself change that shape and wraps around the cell particle or the particle maybe it's a piece of food and eventually engulfs it into a vesicle the opposite endocytosis and exocytosis it's basically pinocytosis in reverse a vegetable moves the side of the cell membrane joints with it fuses it's vesicle with the cell membrane and expels the particle out of the cell we shut your remember scale if we Zoom to this line we have to understand it. This black line represents this possible lipid bilayer that we've been zoomed in on large particles can get in and out of a cell but not through the cell membrane yet wrapped up in a piece of the cell membrane called a vesicle and that raps video on the properties and structure and function of the cell membrane I'd hoped in this video to get to a discussion on tonicity in the relative concentrations feed Solutions I think I have to do like a little of three minute video on that separately so check back for that soon
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Phuong Nguyen
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