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, commenting on the comment section, but most importantly please subscribe.
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But let's talk about cell membrane. So when 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 we'll 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 They have these little 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.
It's really, really important and we'll talk about it later. It's called the glycocalyx. 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 lipids. What I want to do is I want to take a piece of this actual cell membrane and we're going to zoom in.
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. So 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 specifically something really, really cool, and it's made up of phosphates and sphingocides.
Sphinocides. Or sphingocines. Now these are really, really cool. So phosphates and sphingocines, basically, what I want you to remember is that they have a negatively charged surface to them.
They're negatively charged. 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 phosphatidyl Choline. Another one is the sphingocenes, and there's a very specific one here called sphingomyelin. But these are basically going to be the phosphates and sphingocenes 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 phosphatidylserine. 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 hydrophilic, which is a beautiful concept here, because it allows for it to interact with the extracellular fluid, 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. concept. Alright, so we know now that the outer membrane and the inner membrane is made up of phosphates and sphingosines. Particularly in the outer is phosphatidylcholine and sphingomyelin.
On the inner it's phosphatidylserine and if you really wanted the extra one here I'll write it down. This one is called phosphatidyl 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 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 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 extracellular and intracellular. 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 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 and 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 thing called sphingocenes.
On the outer, sphingomyelin and phosphatidylcholine. On the inner, phosphatidylserine, phosphatidylethanolamine. Big thing to understand is they're negatively charged, so they very nicely interact with water because they're polar. In the inner, 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 membrane. You saw 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 transmembrane 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.
The other 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 un-strong like kind of covalent bond. So these are very, very strong bonds, and that's another important concept to take away. Alright, so that covers again membrane proteins.
These are proteins which either completely are kind of invaginated 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 glycocalyx.
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 how it's 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. This is called your glycoproteins. 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 and the sphingocenes, 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 what 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 friends, so let's actually start talking about the functions of the cell memory. 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 with membrane proteins.
They've got 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. Glycocalyx 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 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 glycoprotein. And? glycolipid, can't forget about that poppy 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. 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 MHC1 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 nucleated cell from a foreign cell. So this is a very specific type of structure, a very specific one.
So the amniotic... 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 detect that that's a normal MHC1 complex. It'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 MHC1 component. So this is not a MHC1 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 AB, 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 in blood typing.
And so that's one way that can help to recognize our cells, our red blood cells of the person versus another person's who maybe doesn't have the specific A or the B or the AB. Maybe these are very different. So maybe this donor's is some type of different red blood cell.
So let's say that in this patient, maybe all of these, his blood type, these 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 glycocalyx proteins, to cause it not to agglutinate and therefore not to clot. 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 lipids, so we know that glycocalyx is important for antigenic function and preventing cell dehydration.
The second thing is the membrane lipids. Now membrane lipids are really, really cool, right? 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 and 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 wanna do is I wanna 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, increased space between the phospholipids and increased 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, because they're radiating heat on you, you're radiating heat on them. So that's a similar kind of concept.
That's why I want you to remember it. very very high temperatures the fluidity will increase because I want you to think about the phospholipids 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 that 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 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 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 another 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, here lots and lots and lots of cholesterol guess what false lipids are gonna stick to one another really nicely now and so that's going to be again this concept here for a 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 saturated and saturated kind of me 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 I'm 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 from one another whereas if I'm like a saturated I'm kind of sitting on the plane like this what hate in 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 it's not a little weird but you want to basically increase the amount of unsaturated fatty acids. And that will basically increase the spacing and increase the fluidity. If I want to make it to where it's really tight, kind of compact 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 to 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, very commonly tested. Guys, please don't forget. 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 that you'd hear that, right? But it's pretty cool. So one of the concepts that I want to talk about is this concept of like simple diffusion across the membrane. So across the membrane.
And this is really, really cool. So when you think about it. 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 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 Heroin hormones is a really really big one as well. So it really has to be small, non-polar, or lipid soluble to be able to simply diffuse without any kind of ATP involvement, but to dissolve across the cell membrane.
And I like to remember that like dissolves like. So if it's small, non-polar, 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 non-polar, we need things that are very, very tiny that can fit between the hydrophobic tails or between the phosphate groups. 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 phospholipids 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 phosphate groups and you were to follow it, 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. 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 phosphate groups, you'd be able to see it at some point, maybe in the inner membrane, maybe later you'd see it in the outer membrane, maybe later you'd see it in the inner membrane.
That's called transverse diffusion. And that's what happens. reverse diffusion and we need specific enzymes really that help us to perform that type of task and I just remember it by where they're Going so if it's going from inner to outer then it's a flop pace. I'm not even kidding. I'm not making this up It's literally called a flop pace and then if it's going from the outer to the inner then this one is called a flip pace.
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, and types of fatty acids. Knowing that the transport across the cell membrane is important. So simple diffusion of small non-polar lipid soluble molecules that easily dissolves across the cell membrane.
And then lastly, knowing that 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 friends. 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-soluble. 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 the 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 may be 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, like dissolves like. What's another function? Well, let's say here I have a vesicle and this vesicle in order for me to be able to stimulate it to fuse with the cell membrane and release these particular molecules, I have to have a hormone.
Let's say this is a hormone. It has to bind on to 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, and then produce a response. That's another important concept of proteins. Another cool function is they can link a cell one and cell two 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 when we get to cell junctions, but this could be things like tight junctions. All right, we'll talk about these. This could be things like your desmosomes. All 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, or some type of substrate. So we usually 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, we 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 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, cell two. Maybe I want...
this cell to become activated. So I want ions, positive ions to flow from this cell into this cell. You know 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's 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 of 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 hemidesmosomes. They actually allow for that kind of process here. So we can call one of these as an example, is hemidesmosomes. 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 the semipermeable 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. 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, and as always, until next time.