foreign what's up Ninja nerds in this video today we're going to be talking about the cell membrane before we get started I really hope that if you guys do like this video you find a lot of benefit from it please support us and one of the best ways that you really can do that is by hitting that like button comment down the comment section but most importantly Please Subscribe also we got some awesome illustrations and notes that I really suggest you guys go down in the description box below check out our website and you guys can follow along with me as we go through this I really think it'll enhance your learning experience but let's talk about cell membrane so we go through the cell membrane I want us to go through the structure and the function right so the two components here the structure of the cell membrane well first what does the cell membrane do like what's its kind of overall justificational purpose really the cell membrane is just supposed to act as a barrier between the intracellular and the extracellular fluid there's a lot of different components of it though so when you look at the structure you see this kind of like black thin membrane here that's the cell membrane and the cell membrane is made up of very very special components of it so this black part that will actually zoom in and look at here is called the membrane lipids that's the first part that is actually super super crucial and there's so many different components here such as phospholipids such as the actual fatty acids such as cholesterol so we'll go through all of that the second component here is going to be these orange proteins that are kind of spanning the cell membrane or linked on the inner or outer surface these are called membrane proteins and there's so many different types of these as well and they have various different functions okay and then the last component of the actual cell membrane is that you see on these actual proteins these membrane proteins they have like these little like extensions of lipids and sugar residues which are represented by the pink and then this baby blue color this is like glycoprotein glycolipid Network on the outside of the cell and it's really really important we'll talk about later it's called the glyco calyx so those are the three components that make up the structure of the cell membrane let's dive into each one of them and talk about it the first thing is the membrane lipid so what I want to do is I want to take a piece of this actual cell membrane and we're going to zoom in on it as you see here and then on this side here this is the extracellular fluid so this is the fluid outside of the cell and then here is the intracellular fluid the fluid inside of the cell so this is inside the cell outside the cell now when you zoom onto this membrane you see a lot of different cool things right the first thing is you see these kind of like blue dots if you will see these blue circles these are actually called your phospholipids so there's an outer membrane our outer membrane inner membrane and that's made up of the phospholipids okay so the outer membrane and inner membrane have been specifically something really really cool and it's made up of phosphates and sphingocides sphingocides are sphingosines now these are really really cool so phosphates and sphingosines basically what I want you to remember is that they have a negatively charged surface to them they're negatively charged so phosphates have a negative charge to them and sphingosines have a negative charge to it the specific concept that I want you to understand is that these are actually Associated on the outer membrane and on the inner membrane now if you really wanted to look at it like this the outer membrane is actually made up of very specific types of phosphate groups one of them we call phospha to dial choline another one is the sphingosines and there's a very specific one here called sphingo myelin right but these are basically going to be the phosphates and sphingosines that make up the outer membrane of the cell on the inner membrane of the cell it's still phosphates we just give them a very specific type of phosphate component here and these are called phospha to dial serine and then there is other ones like ethanolamine but basically the big thing that I want you guys to understand here is that on this outer membrane and on this inner membrane you have phosphates and sphingosines which basically have a negative charge to them which we'll talk about later gives them a certain degree of polarity in other words they love to interact with water because they have a charge to them so therefore this phosphate and sphingosine groups that are on the outer aspect of this phospholipid bilayer they are hydrophilic so this component here is hydro Philip which is a beautiful concept here because it allows for it to interact with the extracellular flu which is water and it's hydrophilic here which allows for it to interact with the water in the intracellular fluid so that's a really really cool concept all right so we know now that the outer membrane and the inner membrane is made up of phosphates and single scenes particularly in the outer it's phosphodel choline and sphingomyelin on the inner it's phosphoidal serine and if you really wanted the extra one here I'll write it down this one is called phospha to dial ethanolamine ethanolamine is the other one but basically it's phosphate groups that have negatively charged that make them hydrophilic that's really the big thing I want you to give the second component is these like little red squiggly lines that are coming from the phosphate head what is that those are fatty acids so this component here that are coming from these phosphate heads is fatty acids so the second component is going to be your fatty acid chains now the fatty acid chains are really important in the sense that they're made up of two types of fatty acids that are actually going to be as kind of stuck within the center part in between here so in here is the fatty acids all of these and the big thing I want you to understand about these puppies here is that they are hydrophobic they're hydrocarbon chains they hate water they do not want to be anywhere near water and that's why they're tucked in between they do not come into contact with the exercise of the fluid Isn't that cool so the fatty acid chains here there's two types they're saturated which just means that it's kind of like these straight components here a lot of hydrocarbon chains in there or it can be unsaturated which may have may have a double bond in it which gives it this special type of Kink to the actual structure which is really really important we'll talk about later when we get into fluidity but these are the big things that I really want you to understand the last component here of the membrane lipids is going to be these kind of like pink structures these pink circles that are kind of extended or kind of deposited into the cell membrane you see how they're deposited into the cell membrane this is cholesterol this is cholesterol and cholesterol is very very important for the actual stability of the cell membrane and we'll talk about later how cholesterol has a very significant involvement in what's called fluidity so the big thing to understand as a quick recap here is we have again membrane lipids as one of the components here what is it made up of three particular things outer membrane inner membrane which interact with the water between the intracellular and extracellular fluid is having these phosphates the phosphate head of the phospholipids or if you really want to be a little Advanced these things called sphingosines on the outer sphingomyelin and phosphatidyl choline on the inner phosphatidylserine phosphatidyl ethanolamine big thing to understand is they're negatively charged so they very nicely interact with water because they're polar in the inner in between coming extending from the phosphate and sphingosine heads in the center is these hydrocarbon fatty acid change they're saturated meaning no double bond unsaturated has a double bond which gives a little Kink to it we'll talk about why that's important later but these hydrophobic they don't like that water so that's why they do not interact with the fluid of the intracellular and extracellular fluid and then lastly cholesterol is deposited into the cell membrane as well these are the big components let's now come down and talk about the next important component of the cell membrane and these are the membrane proteins so membrane proteins are really really cool and they can actually be completely spanning the entire cell memory you see how it goes from the outer membrane all the way to the inner membrane and allows for a connection if you will where maybe certain things can kind of travel in or travel out these are really really cool these proteins because they span the entire membrane we call these integral or specific type a transmembrane protein so again what is this one here so this one here specifically it spans the entire cell membrane this can be called an integral this is an integral protein but a very specific type of it spans the entire membrane which is the most common type of integral protein this is called a trans membrane protein and this is a great example of like your Ion channels or your carrier proteins these basically have the ability to interact with the extracellular fluid and the intracellular fluid that's a pretty cool concept they're ones are proteins that basically are linked kind of like very very weakly so in other words they may have like slight positive charges slight positive charges that allow for them to be able to interact with the phosphate groups because phosphates are negative and sphingosines are negative these are called peripheral proteins so these are called peripheral proteins and again I think the big thing to understand here is that integral proteins you see how they're completely spanning the entire membrane these have a strong kind of lipid Bond so they have a very intimate kind of like strong bond between the phospholipid bilayer very strong whereas this one here your peripheral proteins these have a weak type of lipid bond in other words they do not love to interact with them so it's a very weak more like hydrogen bonding so if you really wanted to remember this one's your hydrogen bonding where this one may be more of an unstrong like kind of covalent bond so these are very very strong bonds and that's another important concept to take away all right so that covers again membrane proteins these are proteins which either completely or in kind of invaging into the cell membrane and they may span the entire membrane transmembrane this is an integral type or they can have a weak interaction with the cell membrane electrostatic hydrogen bonding and they do not span it these are peripheral proteins okay next thing is let's talk about the glycocalyx all right so the next component here is the glycocala so the glycocalyx is really interesting so we have the protein structure here right so here's our proteins that are basically again you could have the two types the integral which if it spans the whole membrane it's called transmembrane or if it's kind of see a softly linked to the inner outer surface again these are the peripheral proteins but sometimes these proteins can have these kind of like sugar residues kind of linked up to them right so we're going to just call this a sugar residue really it's just kind of like an oligosaccharide and so when you have a protein and a sugar kind of combined we call that a glycoprotein and this makes like this really really powerful Network on the outside of the cell so this is called your glyco proteins and this is one big thing the other component which is also kind of crucial is that sometimes you have some of these kind of like lipid molecules I'm sorry sugar molecules which kind of come off of the cell membrane and so because the cell membrane is primarily kind of a lipid complex if you have these sugar residues again this is another sugar residue kind of linking off of the cell membrane and the cell membrane was primarily lipids phospholipids fatty acids cholesterol then this would be called a glycolipid so sometimes we can also have these glycolipids and really the combination of these glycolipids and these glycoproteins kind of form this mesh Network on the outside of the cell and that's what's called your glycocalyx so what I want to do now is we've covered all the structures we've covered the membrane lipids with the components of it so the phosphates in the sphingosines the fatty acids the cholesterol we cover the membrane proteins the integral or the peripheral and we cover the glycocalyx which is the glycoprotein and glycolipid structure on the outer surface of the cell now we got to do is go through each one of those and talk about what are the functions of the membrane lipids what are the functions of the membrane proteins what are the functions of the glycocalyx let's do that now all right my friend so let's actually start talking about the functions of the cell membrane so first one is the glycocalyx right it's the easiest one so we'll cover that one first then we'll go into the membrane lipids they're just a little bit harder of a function and then we'll finish off of membrane proteins they get a ton of functions so first thing is when we talk about the cell membrane again we know the three components right glycocalyx is one of those glycocaly is made up of the glycoprotein glycolipid network on the outside of the cell and what that's really good for is two particular things one is that this really helps the cell to be able to hold on to water so it's really good at being able to regulate the movement of water kind of in in and out of the cell it's really really good at that and so what it's designed to be able to do is to decrease cell dehydration that's a really great thing about this glycocalyx is that it's really really good at being able to reduce the dehydration of the cell because it controls the movement of water in and out of the cell because of this crazy kind of glyco protein and glycolipid can't forget about that puppy there Network on the outside of the cell all right so that's one particular thing the second thing which is actually really really cool is antigenic function so it has a very important type of antigenic function you're like what that mean man so antigenic function is it's really what allows for our cells our immune system cells to recognize something as though if it's host or if it's foreign it's not supposed to be there it's abnormal I'll give you two examples one is with respect to our immune system so our immune system is a really really great example of one so here's a host cell and here's a foreign cell on this host cell it has a very specific type of network of glycoproteins and glycolipids that maybe will make up you don't have to memorize this I just want you to understand it maybe this whole kind of structure here on this host cell makes up something called a MHC one complex and we'll talk about this later when we get into Immunology but this is what basically helps us to recognize a normal human you know nucleated cell from a foreign cell so this is a very specific type of structure a very specific one so the immune system cells will come and what they'll do is they'll read and they'll say okay okay this cell definitely has I can can detect that that's a normal mhc1 complex that's a normal glycocalyx whereas if I go over here and I try to recognize this one this one is not a glycocalyx that I actually recognize it does not have that very classic MHC one component so this is not a MHC one component so therefore I'm going to kill this cell and keep this cell alive and healthy and so that's one of the cool ways so it helps with being able to control our immune system being able to recognize if something is foreign versus our own and the same concept we can think about this with red blood cells so red blood cells have these specific antigens on them these specific glycocalyx molecules that gives them the blood type A gives them the blood type B gives them the blood type a b or they have none of them none of these and so we call that o right so all of these different types of proteins basically help us to recognize what type of blood type the patient has so it's really really cool right so it's very helpful and blood typing and so that's one way is it can help to recognize our cells our red blood cells of the person versus another persons who maybe doesn't have this specific a or the b or the a b maybe these are very different so maybe this donors is some type of different red blood cell so let's say that in this patient maybe all of these his blood type these image these uh glycocalyx proteins all represented type A blood and then you give them this donor which represents type B blood this may not be a compatible type of blood typing and that's an important thing so it would help our actual immune system cells to be able to recognize that this is foreign not our actual blood cell that we should accept and this one is good because it can recognize these different types of antigens on the surface the glycocalyx proteins and if it notices something that's different it'll actually release antibodies to bind to the donor red blood cell proteins and cause them to Clump and Destroy whereas it will not release any types of antibodies to actually combine with these proteins these glycocalic proteins to cause it not to agglutinate and therefore not to clod so that's a really really cool thing so the big things that I want you to take away from the glycocalyx is that it prevents cell dehydration and it plays a very very important role in acting an antigenic function recognizing our cells from foreign cells and that's a really important thing with the example of the immune system and blood typing okay now let's come and talk about the membrane lipids and all the functions they have all right so when we talk about the next component which is the membrane lipid so we know that glycocalic is important for antigenic function preventing cell dehydration the second thing is the membrane lipids now membrane lipids are really really cool right and in a very specific way there's two very important components to the function of membrane lipids one is called fluidity so it's the ability of the cell to adapt its shape and movement and it's really really cool and I'll give you a great example of that when we get over into the next part of the lecture here but with fluidity there's three important factors that you guys will be tested on that influences the degree of the actual cell to adapt its shape and movement in other words does it want to be rigid in a very tight structure not a lot of movement going on or does it want to be a little bit more relaxed open and allow for more movement and Mobility so the three important components that influence that my friends very very important is temperature so temperature has a very profound effect on fluidity so hot and cold the next one is the presence of cholesterol so cholesterol believe it or not I told you it has a very important component to the stability of the cell membrane it controls fluidity of the cell membrane and the last one is the types of fatty acids and you guys remember the fatty acids that are basically in the center of that actual structure to the actual cell membrane right we said that there's the fatty acids there's the hydrocarbon chains which are the hydrophobic portion now these are the three things that affect fluidity the ability of the cell to adapt its shape and movement now let's think about this and what I really want to do is I want to talk about what Will basically with these particular factors increase or decrease fluidity so if we increase fluidity what do you notice there's a lot of space between the phospholipids in all of these structures there's a lot of space do you notice that between each one of these if there's a lot of space there's a lot of degree of movement here as well so there's an increased fluidity increase space between the phospholipids and increase kind of movement now with temperature I just want you to make it too very very simple if it's really really hot really really hot you're going to want to be sitting close to somebody no no because they're radiating it on you you're radiating heat on them that's a similar kind of concept that's why I want you to remember it so a very very high temperatures the fluidity will increase because I want you to think about the phospholip is just kind of separating from one another this is very very crucial when it actually comes to the presence without cholesterol the other concept is if we decrease fluidity so if it's high temperatures whenever it's really really cold what do you want to do you want to snuggle up to somebody you want to get close to your friend your family member your dog whatever it may be to kind of get really really warm right so you guys can radiate heat on each other so you guys get close to one another and so really really low temperatures especially in the presence without cholesterol I need to write this down especially without cholesterol then these dang phospholipids will get tight with one another and the cell membrane will get rigid and very very tight and again not allow for a lot of movement and mobility of the phospholipids same concept for cholesterol cholesterol I want you to think about when cholesterol is present and high amounts it really causes the phospholipids to come and stick Imagine It Like Glue so if there's lots of cholesterol it'll stick it'll act like a glue to stick the phospholipids close to one another if there's very little cholesterol the phospholipids won't have the glue to stick with one on there and they'll drift apart so in this situation this would be very little cholesterol very little cholesterol and then in this particular so again here's the one specific example when cholesterol is low you would think oh that increased fluidity but Zach you said over here that low temperatures without cholesterol this is the only other exception that when cholesterol is low if it's at Cold temps it'll compact the actual phospholipids down but if we go over here lots and lots and lots of cholesterol guess what phospholipids are going to stick to one another really nicely now and so that's going to be again this concept here for a decrease decrease in fluidity now last one here is types of fatty acids this one's actually really cool so remember I told you that there's two types of fatty acids one is it's saturated and saturated kind of gives you this straight beautiful line like this one and then unsaturated has a double bond and the double bond gives a little Kink to the structure now imagine if I'm trying to sit next to somebody and I'm like this legs wide open arms wide open can the phospholipids be close to one another no and so they separate out very far over one another whereas if I'm like a saturated I'm kind of sitting on the plane like this we're hating my life right really really close arms close together legs close together I can fit a lot of things on the side of me so that's the same kind of concept here that if we want to increase fluidity put some Kinks into the mix that's a little weird but you want to basically increase the amount of unsaturated fatty acids and that'll basically increase the spacing and increase the fluidity if I want to make it to where it's really tight kind of impact structure then I'll basically increase the amount of my saturated fatty acids no double bond No Kink and therefore these can kind of tightly compact one another and this is the concept that I want you to understand about fluidity this is very commonly tested all right now that we understand one of the big functions of the membrane lipids let's talk about one more which is again going into the transport concept all right so the next thing with membrane lipids not only is their fluidity is a very important concept A Very commonly tested guys please don't forget that please the next thing is there's a concept of Transport so the movement of things and this could be things that are actually moving across the cell membrane or it could be things that are moving within the cell membrane you didn't think it should hear that right but it's pretty cool so one of the concepts that I want to talk about is this concept of like like simple diffusion across the membrane so across the membrane and this is really really cool so when you think about it the cell membrane is a phospholipid bilayer phosphates on one side phosphates on the other side and then the fatty acids in the core of it right that's what we know phosphates and sphingosines are on the inner and outer because they're negatively charged hydrophilic and then fatty acids hydrophobic in the inner side now what's really really important is that certain substances have the capability of moving across this cell membrane in and out but the way that these things move across is because the lipid bilayer has on this inner surface these fatty acids it's very very hydrophobic right so again the hydrophilic component is yes this thing on the outside but this is the problem here it's this is the problem this component the hydrophobic component so whenever things have to move through they have to be able to dissolve within this hydrophobic component and so examples of things that are able to move across here is things like oxygen and CO2 that's one another one is things that are like a small small structures so very very tiny structures other things that are really really important here are things that are lipid soluble and so lipid soluble structures so steroid hormones is a really really big one as well so it really has to be small nonpolar or lipid soluble to be able to Simply diffuse without any kind of ATP involvement but to dissolve across the cell membrane I like to remember that leg dissolves like so if it's small nonpolar and lipid-soluble it's just like the cell membrane it'll easily dissolve and move across the cell membrane so I want you to use that terminology that like dissolves like that because this cell membrane especially the inner component is hydrophobic it's nonpolar we need things that are very very tiny that can fit between the hydrophobic Tails or between the phosphoid phosphate groups or we need something that's nonpolar like the hydrophobic Tails or hydrophobic in other words lipid soluble that can diffuse easily across the cell membrane that's one concept the other one is diffusion within the membrane diffusion within the membrane and I just think that this is super super cool I don't want you guys to get too crazy I just find it so fascinating that when you think about the cell membrane right we know that we have these phosphate groups and we know that we have the phosphate groups on the inside and the outside and then we have the hydrophobic Tails do you know that they can move I could literally move this phosphate group here to here and I could move this phosphate group from here to here and it's constantly happening they're constantly moving the fossil lipids are constantly moving from side to side within the membrane you know what they call this they call this lateral diffusion so they literally call this lateral diffusion and what's really cool is if you were to tag let's say that you just tagged one of these philosophy groups and you were to follow you would see it just moving all around the cell membrane it's so cool the other concept here is that if I have a phosphate group here I could move it to the inner membrane so I can move it from the outer membrane to the inner membrane or if I wanted to move this from the inner membrane to the outer membrane I could do that as well so you can flip flop back and forth between the actual inner and outer membrane so if you were to tag one of these philosophy groups you'll be able to see it at some point maybe on the inner membrane maybe later you'd see it in the outer membrane maybe later you'd see it on the inner membrane that's called transverse diffusion trans verse diffusion and we need specific enzymes really that help us to perform that type of task and I just remember by where they're going so if it's going from inner to Outer then it's a flaw Pace I'm not even kidding I'm not making this up it's literally called a flop haste and then if it's going from the outer to the inner then this one is called a flip paste I wish I was making this up but these are enzymes that are basically helping to move these phospholipids from one end to the other from the outer to Inner inner to Outer it's really cool but that covers the basic concept of the membrane lipids so fluidity is one really really important component knowing the three things that influences that temperature cholesterol types of fatty acids knowing that the transport across the cell membrane is important so simple diffusion of small nonpolar lipid soluble molecules that easily dissolves across the cell membrane and then lastly knowing that the phospholipids can actually easily travel along the cell membrane in a lateral pattern or they can flip-flop back and forth between the outer and the inner membrane and then now what we're going to do is talk about the membrane proteins in their function all right my friend so now we're going to talk about the membrane functions particularly pertaining to the membrane proteins so this is the integral proteins which is specifically the transmembrane protein and the peripheral proteins what can they do there's a lot of things that these things can do so we told you that the membrane lipids only allow for what type of diffusion simple diffusion of small nonpolar lipid soluble molecules well there's lots of other molecules that are large polar and water solid valuable what about those how do they get across the cell membrane we need transport proteins to be incorporated into the cell membrane transmembrane proteins to act as channels or carriers to move those large polar and water-soluble molecules across the cell so we may need again this type of channel protein so this is a channel protein this may be a carrier protein and what they may do is is they allow for what type of transport very large large polar and what else water soluble transport of things across the cell so that's really really important so it'll allow for things like charged molecules to move across the cell allow for things like proteins to be able to move across the cell so that's really really really important now another really cool concept here is that proteins are not only involved kind of in being embedded into cell membrane they can be transient in other words they can kind of move and attach so remember these peripheral proteins maybe there's peripheral proteins that are on the inner cell membrane you know here maybe molecules that I want to either move to the cell membrane to release and we call this exocytosis so exocytosis or maybe there's molecules that I want to bring in to the actual cell so this is called endocytosis this is another example of where proteins can kind of cooperate this process and you know what's really also cool look how the phospholipids of this vesicle fuses with the lipids of this cell membrane look at how the phospholipids of this cell membrane forms this phospholipids of that vesicle that's an example of fluidity so I love this example of exocytosis and endocytosis because this is one of the perfect examples of these two exhibiting a concept of fluidity I just think it's so darn cool how that happens but that's one of the functions of membrane proteins is they allow for transport of very large water-soluble polar molecules across the cell membrane that wouldn't easily dissolve across the lipid-soluble hydrophobic fatty acid tails of the actual cell membrane remember light dissolves like what's another function well let's say here I have a vesicle in this vesicle in order for me to be able to stimulate it to fuse with the cell membrane release these particular molecules I have to have a hormone let's say this is a hormone it has to bind onto a particular type of receptor and when it activates or stimulates this receptor it sends signals that then will fuse actually activating this vesicle to fuse with the cell membrane so it may activate some type of second messenger system which is actually pretty cool so there's another function it allows for me to be able to take an extracellular so this is the extracellular fluid here's the intracellular fluid it allows for something in the extracellular fluid to stimulate a protein trigger a signal in the cell in the produce a response that's another important concept of proteins another cool function is they can link a cell one in cell 2 together so there may be these integral proteins that are on the outer surface of the cell that link to the integral proteins of another cell and that's a really cool concept we'll talk about these a little bit later um when we get to cell Junctions but this could be things like tight junctions right we'll talk about these this could be things like your desmosomes right we'll talk about these this could be things like adherence Junctions and we'll talk about these so this is a really cool concept of where you have these structures that allow for cells to link up with one another if by some chance you understand pathology where maybe I destroy these cell adhesions and the cells can't stick with one another and they start separating that's an important concept okay what else we come down here we know that the next functions that are also really really key here is going to be enzymatic function believe it or not let's say that there's actually some type of enzyme out here let's say or some type of substrate so we usually we represent substrates as a plus b right maybe there's an enzyme here on the outer surface of the cell and in order for this to be able to become activated and turn into C let's just say c plus d c plus d this is the reaction they use this as a common reaction this enzyme this is our enzyme he's the one that catalyzes or stimulates the acceleration in this particular step so he will allow for the increased speed of reaction same concept maybe it's inside of the cell maybe it doesn't have to just be outside the cell a plus b will have to interact with this enzyme and make C plus d he will stimulate this is an enzyme this is an enzyme and they may stimulate the intracellular and extracellular synthesis of particular types of substrates that's a really cool concept so so far we've got transport we also have what other thing transport we have cell to cell communication we have a receptor we also allow for enzymatic function another one is cell communication so again cell one sell to maybe I want this cell to become activated so I want ions positive ions to flow from this cell into this cell and we call these and they're very common in muscle cells Gap Junctions so this is another example of something that we'll talk about later when we talk about cell Junctions called Gap Junctions very cool concept the last but not least thing that's actually really important here is going to be the cell attachment to The extracellular Matrix so you know whenever we have cells like epithelial cells epithelial cells they love to connect with the outside surface sometimes to give stability to the cell membrane so sometimes we have like little connective tissue structures that are nearby here's some connective tissue okay so here is going to be the connective tissue that we're zooming in on so here's this we're zooming in on this connective tissue that these cells are linked with in order for us cell to kind of be really strengthened to the outside surfaces in this case the connective tissue lining or the basal lamina we need the proteins of the cell membrane to link with the connective tissue of the extracellular Matrix and this is that connection right here these linkage between the two and this is important because there's a lot of different things that do this a lot of different structures right but this is a really really important thing that I need you guys to understand one great example is like hemidezmosomes they actually allow for that kind of process here so we can call one of these as an example is Hemi desmosomes in this video we will be discussing the structure of the cell membrane when scientists looked at the selectively permeable cell membrane they described its structure as a fluid mosaic you might know that a mosaic is a picture made up of little tiles like a mosaic the cell membrane is made up of different parts as well the cell membrane has two layers of phospholipids referred to as a lipid bilayer the lipid bilayer isn't rigid the phospholipids in it have the ability to move in a flexible wave-like motion let's take a closer look at a few phospholipids the round head portions are hydrophilic which means they are attracted to water both the extracellular fluid meaning fluid outside the cell and the cytoplasm inside the cell are mostly made up of water so the hydrophilic phospholipid heads of the outer layer will be oriented toward the extracellular fluid and the heads of the inner layer will be oriented toward the cytoplasm the phospholipid tails are hydrophobic which means watery areas repel them so they Orient toward each other in a direction as far away from the watery content as possible there are also scattered proteins embedded in the phospholipid layers some with carbohydrates attached so in the fluid mosaic model the cell membrane is made up of different parts and these parts make up a flexible boundary around the cell but how do the majority of substances get in or out of the cell some molecules seep through the little spaces in between the phospholipids which make up the majority of these semi-permeable cell membrane however other molecules are too big to fit through the cell membrane this way so how do these larger molecules pass through the cell membrane the molecules move through proteins embedded in the cell membrane either from the extracellular area into the cell or from the intracellular area out of the cell these substances will move through tunnels made up of these proteins we'll explore how things move through the cell membrane in Greater detail separately [Music] so that really covers all the functions of the membrane proteins the membrane lipids the glycocalyx and all the components of the cell membrane I hope it made sense I hope that you guys enjoyed it and as always until next time [Music]