Understanding Cell Membrane Structure and Function

Today we are starting a series of lecture on a very very basic topic in the medical sciences that is the physical structure of a cell, right. First of all I will discuss about the structure and function of the cell membrane. Cell membrane is also called plasma membrane of a cell, right. So let's talk about the structure of a cell membrane. Let's suppose here is a cell Suppose we take a typical cell here, right? Now all of you know that cell has a basic structure, it has a nucleus and there is cytoplasm and it is surrounded by the cell membrane, There is sight of detail. right? into detail of the structure of the cell membrane. Primarily cell membrane is made of phospholipids and associated proteins. Again what are the basic two components of cell membrane? This is made of phospholipids and associated proteins. Is that right? Now, let me draw this structure right in detail. Basically, this cell membrane is a double layer of the molecules. Primarily it is a double layer of molecule. Because it is double layer of a layer of molecules, so it is also called lipid biome. layer because it has lot of lipid and it's a double layer of the molecule it is also called lipid by layer. Now let me draw a component of it. There. The basic component. Suppose this is a cell and I just draw cell membrane in detail from this point up to this point only right first of all the basic component is phospholipid now phospholipids are what phospholipids are having one part which is polar right this is the polar part of the phospholipid here there is phosphate and with that it is having fatty The cells have the acid. acids. What is it? fatty acids. This is the basic molecule which is going to make cell membrane. What is it? Acid. This is the basic molecule. So in the cell membrane there are phospholipids and it has one polar compound, It has one acid. See how a lot of the cells make the cells. polar end and other are fatty acids. Right? Now we have to see how lot of these molecules make the cell membrane. Before we go, how do you... Before we go how these molecules are oriented you must know that extracellular environment is aqueous environment. There is a lot of water outside the cell, outside the cell membrane and there is lot of water inside the cell membrane. So it means extracellular environment is aqueous. So it means it was, Aqueous environment. And intracellular environment is also aqueous. Is that right? There is water outside the cell and there is lot of water inside the cell. it was, So it means this cell membrane is separating extracellular aqueous environment from the, it was, it was, yes. yes, intracellular aqueous environment. Is that right? The polar comes polar, Now, you must be knowing that polar compounds dissolve into polar compound. Thank you. Right? This is polar component of the phospholipid. these two fatty acids, Because this is polar, it has some charge. It is water soluble end of the molecule. these are not... And these two fatty acids, these are not water soluble. These fatty acids are not water soluble. of the molecule which is water soluble it is called hydrophilic. What is this component called? hydrophilic. And this component which does not dissolve in water this is called hydrophilic. So we can say phospholipid molecule have hydrophilic component, they have a head which is hydrophilic and they are having tails which are hydrophobic. Is that right? Now what really happens that in this part of the membrane, this water soluble part will be oriented outward towards the head. right and what are here these are yes please fatty acids and these are hydrophobic is that right now actually this is one layer other layer will be on this side layer of the molecules now you can see that cell membrane is made of double layer of phospholipids right Made of double chondromal. I have shown you the molecular structure of the cell membrane. Now, Now question is that why these molecules of phospholipid are oriented in such a fashion? that is oriented in such a fashion. Answer is very simple. Answer is very simple. You know these component fatty acids they are not going to dissolve into water. You know these components fatty acids they are going to dissolve into water. They avoid water. They are hydrophobic. So it means this water outside and water inside. They avoid they are hydro. So outer layer of the molecule this hydrophobic component will be directed away from the water and in inner layer again these fatty acids will be directed away from the water so they will be directed towards each other is that right This water outside in inner layer again these fatty acids will be directed away from the water. So they will be directed towards each other. So what we can really see that fatty acids right they dissolve into each other. See that acid, right, they dissolve into each other. They attach with each other. They attach with each other. They are oriented towards each other. They are oriented towards each other. Just like you put a drop of oil and another drop of oil in the water. Just like you put a drop of oil and another drop of oil in the water. Oil drops will fuse with each other. Oil drops will fuse with each other. You take a little bit of water put two drops of oils. You take a little bit of water, put two drops of oil. Eventually what will happen to those drops of oil? Eventually what will happen to those drops of oils? Oil dissolve into oil. Oil dissolves into acid, Is that right? In the same way is water right? The same way, the side... outside, water inside and this is something like oil, inside this is something like oil fatty acid so they are oriented towards each other and they make the central portion of the cell membrane these blue parts right this is charged part or polar part or hydrophilic part hydrophilic means water fatty acids. So they are oriented towards each other and they make the central portion of the cell membrane. But as you know these blue parts right of the phospholipids this is charged part or polar part or hydrophilic part. Hydrophilic means water loving part. This component is also water loving. This component is also water loving. So fatty acids which are in the outer component they are So fatty acids which are in the outer component their fluid part will be oriented outward. what is this? hydrophilic part will be oriented outward and phospholipids which are inside inner side of the membrane their hydrophilic component will be directed towards the inner side. And phospholipids which are inside inner side of the membrane directed towards the inner side. So what really happened that cell membranes are made of double layers of phospholipids and phospholipid molecules are oriented in such a way that in So water is made of double layers of phospho. oriented in such a way that in each layer fatty acids are directed towards each other and fillet, each layer fatty acids are directed towards each other and hydrophilic polar components of phospholipids are directed towards the external environment, polar components of our lipids are directed towards this. aqueous environment or they are oriented towards the internal aqueous environment. Am I clear? This is the very basic structure. We have not talked about the associated proteins. Now another thing, you see the core of the cell membrane You see the core of the cell membrane is having lot of lipid inside. is having lot of lipid inside. What is this? This is all lipid. So it means those compounds which are highly charged or those compounds which are very large, That means those compounds which are very large, can they directly? can they directly enter into cell? No. Only those things can enter. No, because only those things can enter, cross this membrane which are lipid soluble. You know core of the membrane is made by the lipid. Is that right? So if there is some substance here which is lipid soluble, So if there is some substance here which is lipid soluble, it can dissolve into membrane and come in. it can dissolve into membrane and condiment. Or there is any other substance which is lipid soluble inside, Any other substance which is lipid, it can dissolve into membrane and go out. it can dissolve into membrane. Right? So which substances can cross the cell membrane easily? So which substance easily? Which substance we can cross in easily? Which substances can cross the cell membrane easily? Substances which are lipid soluble and substances which are very small molecular weight. Substances which are lipid soluble and substances which are very small molecular weight, So we can say that... right? So we can say the substances which are lipid soluble or substances with very very small yes molecular weight, Yes, this is going to go out. these substances can directly go into the cell or if these substances are inside they can easily go out Why? Because they can dissolve into lipid and pass through that. they can dissolve having charges But other substances which are larger molecules or those substances which are highly polar. Polar substances mean which are having charges on them. For example, this is another substance and this substance or molecule is having charges on it. on it it's a polar compound. Can it dissolve into lipid? So can it enter directly into cell? Can it enter? No. So it will be repelled away. In the same way let's suppose this is another compound and this is very very large compound. same way let's go can If it's very large compound can it dissolve into lipid and can it go out? No. What does it mean then? It means that this lipid component of the membrane is providing the permeability barrier for the large compounds and for the highly polar compounds that they cannot pass through membrane. it dissolve me It means if some very large molecule has to come in or and we'll have to move through any large molecule or polar or charged molecule has to move through the membrane it has to have some special facility to pass through the membrane. Let me repeat it. I just said up to now that cell membrane is made of lipid bilayer primarily and associated proteins, the routine that is right. Proteins I did not discuss up to now. And in lipid bilayer what is happening mainly it is consisting of phospholipids. mainly it is a tail guard for fatty acid and polar head size it Is that right? And phospholipids are having the polar heads and and hydrophobic tails. Hydrophobic tails or fatty acids are oriented towards each other and polar heads of the molecule are either outside towards extracellular aqueous environment or oriented inside to was a core of cell membrane the intracellular aqueous environment. So core of the cell membrane is made of primarily lipids, right. And those substances which are lipid soluble or very small molecular weight, It means they have to pass through the membrane. they can easily pass through the cell membrane. But other substances which are very large molecule or which are having lot of charge on the molecule, We need special arrangement. they cannot pass through the membrane by simple diffusion. Is that right? It means for such substances if they have to pass through the membrane, we need special arrangement. There should be special windows and there should be doors through which these membrane can slip in or out. membrane can slip in or out those special windows or doors within the male dosage component proteins in the cell membrane there are special type of proteins is that right and those proteins you hear that here is a protein Those special windows or doors should be made of such material. within the cell membrane are made of which component? Proteins. In the cell membrane there are special type of proteins is that right and those proteins for example let me tell you here that here is a protein and let's suppose okay This is a protein molecule made of multiple peptide chains and these peptide chains, Let's suppose protein molecule made of multiple peptide chains and these peptide chains, suppose this is one peptide chain, this is second, this is third, this is four, so this is one peptide chain, right? And these peptide chains are arranged in such a way that this is second, this is third, this is fourth, right? And these peptide chains are arranged in such a way that there is a lock. In the center of this molecule, right, there is a longitudinal tunnel. This is a tunnel. This is a tunnel and this is water filled tunnel. And this is water filled tunnel. What is it? Water filled tunnel. What is it? We call it aqueous channel. Water filled aqueous channel. What is it? this channel? this channel has a hole which is full of water and then those substances which are water soluble they can pass through this. What is this channel? This channel has a hole which is full of water and then those substances which are water soluble they can pass through association with the cell membrane. so this is one way one of the function of the proteins that proteins are present in association with the cell membrane phospholipid so that substances are allowed to pass in and out. Such type of proteins which are present in the cell membrane, The type of proteins which are present in the cell members, they are called channels. What are these called? channels and I will tell you the functions of proteins, they are called channels. And I will tell you about proteins, more functions of proteins later. more functions of proteins later. Let's come back to this component. Let's come back to this component, After that I will go into detail of the protein. detail of the protein. Another thing, the types of fatty acids and phospholipids which are in outer leaflet and which are in the inner leaflet, The type of fatty acids, phospholipids. which are in outer leaflets and which are in the inner leaflets, they are not identical. they are not identical. I will go to the proteins in detail. later again listen you know this is the outer leaflet of the cell membrane and this is the inner leaflet of the cell membrane now these phospholipids which are present in outer leaflet This is the spray which is produced for the picture effect slightly different than the phospholipids which are present in inner leaflet. It means phospholipids of outer leaflet and inner leaflet are not identical. So it means outer leaflet phospholipid structure and inner leaflet phospholipid structure is not symmetrical. trickle. They are having asymmetry. What we call this term asymmetry. Asymmetric, Now which are the phospholipids which are present in outer part of the cell membrane? asymmetric, outer part of the dial choline, ok I will write it before you start crying, Number one, these are phosphatidylcholine. Okay, I will write it before you start crying. phosphatidylcholine this is a type of phospholipid right phosphatidylcholine this is present abundantly in the outer reflect right choline, type of papal lipid. this is present abundantly in the outer reflex with it there is another friend so fingo myelin so first part it has cooling and fingo myelin are two types with it there is another friend phospholipid which is called sulfingomyelin sulfingomyelin Myelin. So phosphatidylcholine and sphingomyelin are two type of special phospholipids which are abundantly present in the outer leaflet of the cell membrane. of These are the two phospholipids. Right? Yes, These are the two phospholipids which are present in the yes please? please. Phospholipids which are specially present. outer leaflet. Now we'll talk about what Again, there are two important phospholipids which are abundantly present in the inner leaflet of the cell. phospholipids which are specially present in inner leaflet right again there are two important phospholipids which are abundantly present in the inner leaflet of the cell membrane one is phosphatidylethanolamine One is phospholipid. Asparti Dial I don't know who was man who was putting the names of these put simple name like Carla, Ethylamine It is thick man Joanne I don't know he's sick man who put these names right so the inner part of the cell membrane it is having some funny type of you can say phospholipid phosphatidyl ethanolamine So the inner part of the cell membrane It is having some funny type of Asparti Dial di-dial okay ethanol main right this is one and the second type of phospholipid which is abundantly present in inner part of the inner leaflet of the cell membrane that is called phosphatidylserine phosphatidylserine Right? So because phospholipids in outer part are somewhat different and phospholipids which are present in inner part of the membrane they are slightly different. So we can say that cell membrane outer leaflet and inner leaflet show some degree of asymmetry. show some degree of asymmetry. They are showing some degree of asymmetry. Later on we will learn that another asymmetry that the proteins which are the outer part different proteins which are attached to the Right.. Later on we will learn that another component add to the asymmetry that the proteins which are attached to the outer part are slightly different than the proteins which are attached to the inner part. so not only So not only difference of phospholipid make the asymmetrical situation, Make the asymmetrical situation. Later on we will learn the proteins which are attached to the outer part of the leaflet and the proteins which are attached to the inner part of the leaflet are slightly different from each other. later on we'll learn the proteins which are attached to the outer part of the leaflet and the proteins which are attached to the inner part of the leaflet they are slightly different from each other. each other so they also contribute to the asymmetric situation. So they also contribute to the asymmetric situation. And still later on we will learn that outer leaflet has lot of carbohydrates attached with it. Still later on we will learn the outer leaflet has a lot of hydrates attached. Inner leaflet does not have any significant carbohydrates. But inner leaflet does not have any significant carbohydrate. So it means outer leaflet is having lot of carbohydrate molecules outside, This outer leaflet is having lot of carbohydrate molecules outside. inner leaflet does not have carbohydrate molecules. Inner leaflet does not have carbohydrate molecules. Again this difference of carbohydrates applied on this leaflet also Again, adds to the asymmetry of the inner and outer leaflet of cell membranes. the difference of carbohydrates applied on this leaflet also at asymmetry of the... I think I need to recap this. I was trying to put a concept in your mind that cell membrane is made of phospholipid bilayer with associated proteins. Is that right? and it is making outer leaflet and inner leaflet and outer leaflet and inner leaflet are not identical. If they were identical, we could say that they are symmetrical but they are not symmetrical. why they are not symmetrical? there are multiple reason. one reason is that phospholipid in outer leaflet are different and phospholipid in inner leaflets are different. second reason the protein associated with outer leaflet are different. leaflet are different and protein associated with inner leaflet are different. Third reason outer leaflet has lot of carbohydrates attached outside but inner leaflet does not have any carbohydrates attached inside. So all these reasons make the outer and the inner leaflet of the cell membrane asymmetrical or non-identical to each other. Ace Metric Lift Anyone who does not clean these works Am I really clear? Anyone who does not understand? Raise your hand, I will run away. Everyone understand? That's good, we can continue. Another thing, in between, in between the legs of these what? Fatty acids, there is some naughty molecule here. It loves to be here. I don't know why. Who knows this naughty molecule? Yeah. Anyone please use your own head. Anyone please use your own head. This is a very special type of lipid. Okay let me tell you I will draw that structure in a large way right and there are their beautiful legs. okay it's little bit I should say having a dancing tendency. Now yeah what are these? these are polar ants right water soluble ants and these are lipid soluble and there are some molecules which love to be here you know naughty type Who will tell me what are these molecules? You know it, I'm sure you know the name of these molecules. We call them cholesterol. Have you heard of cholesterol? So cholesterol is another type of lipid which is present in the cell membrane intercalated in between the legs of the phospholipids. The inter between the legs of the most of the cholesterol molecule is lipid soluble. Is that right? And cholesterol molecule have hydroxyl. This is a Hydroxyl ends are oriented outward. Why? Hydroxyls are polar end. It is oriented inward. So most of the cholesterol molecule is lipid soluble. But their hydroxyl and their polar of charge, So it is oriented inward. But their hydroxyl ends which are polar or charged, they are oriented outward. they are oriented outward. Is that right? We have learned that cell membrane most important lipids are phospholipids but they do have a small percentage of troll molecules in phospholipids. that cell membrane most important lipids are phospholipid but they do have a small percentage of cholesterol molecules intercalated in between the phospholipids. Is that right? Is that right? Any question up to this? Any question up to this? There is no. Very interesting. Another thing very interesting These phospholipid molecules... These phospholipid molecules are really not fixed. They are not fixed. For example, For example, this molecule is present here. this figure is present here. You look around and that may slip on other side. You look around and that is a slip on other side. What does it mean? All these molecules are mobile. Phospholipid molecules are mobile. They keep on moving laterally. They keep on moving laterally. Is that right? Is that right? They are not fixated in their position. They are not fixated in their position and they display the lateral. These phospholipid molecules are mobile. not fixated in their position and they display the lateral movement and this concept of lateral movement is called fluidity of the membrane. movement and this concept of fluidity of the membrane molecules are like a fluid area they are mobile they are not fixed in position is that right so phospholipid molecule they can slip laterally property The membrane molecules are like a fluid. and in a fluid area they are mobile. They are not fixed in a particular specific position. Is that right? So phospholipid molecule along with cholesterol they can slip laterally right? And we say that membrane shows the property of fluidity. of fluidity property of yes Property of? Yes? Fluidity. This is an important property. fluidity you know why it is so important to know that membranes have some fluidity because later which you will learn right sometimes cell has synthesized some let's suppose cell has synthesized a hormone now hormone is hormone molecules are packed into a membrane membrane bound vesicle this vesicle may come and fuse with the membrane. It may fuse with the membrane and these substances may go out. You know many cells secrete substances. For example cells in the pancreas, There will be insulin containing vegetables. beta cell of the pancreas secrete insulin. So within, These vegetables are membrane bound. if it is a pancreatic cell, there will be insulin containing vesicle and these vesicles that Insulin is going to be released. membrane bound and when insulin is going to be released this vesicle will float move towards the membrane and membrane of the vesicle will fuse with the cell membrane and where they fuse a small puncture point is made and insulin will go out and This moves towards the membrane and membrane to diffuse with the insulin will go out. then due to fluidity it will seal it will be completely closed is that right It will seal, it will completely close. If this was a fixed membrane, If this was a fixed membrane, can it easily go out? No. So this process is called exocytosis. this process is hydrophilic. The cell is showing exocytosis. So, it's fluid, it is important. So if fluid it is important so that cell can show exocytosis. Sometimes cells are in a mood to eat something. In a mood to eat something, Let's suppose here happen to be a bacteria. let's suppose there happen to be a bacteria. Right, this is very sad. You know why? Because cell is going to eat this bacteria if this is a white blood cell. Cell is going to eat this bacteria. Now this is a membrane of the white blood cell, This is a white blood cell. right, and it has produced, catch the bacteria and then this membrane will progressively move to each other and then eventually it will fuse and this will go inside. It has produced a catty of food which has fused. And this will go inside. This process is called endocytosis. What is it called? Again because membranes are fluid, Endocytosis. Again because membranes are fluid. So during the endocytosis a piece of membrane has invaginated and then pushed off, so during the endocytogenesis, right. Still there is no hole in the membrane or will there be any hole in the membrane? the purple liquid comes on the side. There'll be no hole because as soon as it remove away, The same way when this membrane... phospholipid come on the side and seal it. Is that right? In the same way when this membrane from inside going out these phospholipids are added to the membrane. These fossil lipids are added to the membrane. So for the process of exocytosis or for the process of endocytosis membranes must have some degree of fluidity right and then this type of So for the right and this type of membrane biogenesis. what is this? fluidity is also important for membrane biogenesis. Biogenesis means biogenesis means membrane synthesis. you know when cells are initially small when cells divide, You know when cells are initially small, when cells divide, daughter cell are small, daughter cell are small. with the time cells keep on growing. with that cells keep on growing so it means their membranes should also grow. So it means their membranes should also grow. How the membranes grow? How the membranes grow? So it means keep on inserting in the membrane. Cells synthesize new phospholipids and keep on inserting in the membrane and because membranes are fluid so keep on accommodating the new And because membranes are fluid, so keep on accommodating the new molecules and enlarging them. molecules and enlarging the surface area. It means fluidity is important for alpha cytosis. So it means fluidity is important for exocytosis, it is important for endocytosis, it is important for membrane biogenesis, membrane yes biogenesis and fluidity is also right these are some important reasons why fluidity is important. Genesis, yes, fluidity is, right, these are some important reasons why fluidity is important, Now what are the factor which can alter the fluidity of the membrane? For example if phospholipid molecules can more freely move we say membrane is more fluid and if the movement is relatively less free we say membrane is less fluid. fluidity of the membrane. We say membrane is more fluid and if the movement is relatively less free, Now do you know any factor which can alter the fluidity of the membrane? we say membrane is less fluid. can alter fluidity? Temperature. If temperature goes up, Do you know any? membrane will become less fluid or more fluid? It will become neat to explain it, Of course more fluid, there is no need to explain it, all of you must know. all of you must know, temperature increases the movement of the molecules and molecules which are already ready to dance, they will dance more when temperature of the membrane goes up. So this is very easy, no need to remember it even. You don't need to remember the pressure. That increasing temperature increases the fluidity of the membrane. Now another thing, Increasing the corolle content in the fluid, increasing the cholesterol content in the membrane, If we add more and more cholesterol in the membrane, it will increase or decrease. fluidity will increase or decrease? Very good. How do you know that? Yes, very good. How you know that? yeah that's right he knows so well that when you are adding the cholesterol actually you know their legs cannot move now you know they're packed membrane components are more tightly packed when you insert the cholesterol you intercalate the cholesterol molecule in between the phospholipid molecules and membrane become less fluid. So you can say adding the cholesterol make the membranes less fluid. Another thing you know these are the straight fatty acid and this is some what's wrong with this fatty acid yeah what is wrong with this fatty acid Yes, sir. It is having a kink in its leg. Can't you see it? You don't need to call I think Aristotle to discover this. It is not straight, it is having a bend in it. Why it is having a bend? Some fracture there or what? Actually when fatty acids are saturated they are straight. They are saturated, When they are unsaturated they have a kink. they are straight. Saturated, they have a kink. Study in biochemistry one day. you study in biochemistry one day right that's when fatty acids are fully saturated they are straight relatively straight chains and when fatty acids are unsaturated or relatively unsaturated they have bend in their structure Cateosols are fully saturated, they are straight, relatively straight kink. And then cateosols are unsaturated or relatively unsaturated, then they're... not in their leg who told you they have legs and shoes no right now what is there they have a kink now what do you think Right now what is there? They have a kink. What do you think? If in the membrane most of the fatty acid are unsaturated it means they are having If in the membrane most of the fatty acids are unsaturated, it means they are having bends. Bend. This will be more fluid or less fluid? This will be more fluid or less fluid? More. That will be more. It will be more moving leg like this and this. Someone moving leg like this and this people tend to move away or move laterally. People tend to move away or move laterally. So that really happens. So what really happens when fatty acids are relatively unsaturated membranes are more fluid. Is fatty acids valid in me? When you make the fatty acids more saturated and all fatty acids become straight, And when you make the fatty acids acid more saturated and all fatty acid become straight they become tightly packed membrane are less fluid am i clear no problem up to this right we have just talked about the fatty acids they become tightly packed, membrane are less. No problem of today, we have just talked about the fatty acids, the cell membranes are made of double layer of phospholipids. the cell membrane are made of double layer of phosphor, lipid. Is that right? And polar ends of the phospholipids are oriented either outward or inward and hydrophobic fatty ends are oriented to each other. and if polar ends of the fossil lipids are oriented either outward or in the opposite side, fatty ends are oriented to each other. Is that right? Yes, Matrika. Fatty acids in outer leaflets are different than proteins outside and only outer side has different properties. Is that right? Then what did we discuss that this membranes are symmetrical or asymmetrical? They are asymmetrical because type of fatty acid in outer leaflet are different than the type of fatty acid in the inner leaflet. So, if you have a fatty acid in the outer leaflets, it is not a fatty acid. It is a fatty acid. So, if you have a fatty acid in the outer leaflets, proteins outside and inside are different. thirdly outer side has lot of carbohydrate inner side does not. it is is that right? then we talked about fluidity that phospholipid molecules can float around in the membrane so we say membranes show the characteristics of fluidity and why fluidity is important because there is processes of exocytosis going on there are phenomenon of endocytosis going on in the membranes and fluidity there are and then there's membrane then there's membrane biogenesis going on right so due to all these reasons it's very important and membrane should be appropriately fluid, is that right? so that there are no fractures and punctures in the membrane, is that right? they should seal off. They should seal off. then we talked about that fluidity can be increased by temperature but decreased by adding cholesterol or making the fatty acids more saturated, Then we talked about fluidity can be increased by, but decreased by adding cholesterol or making the fatty acids more saturated. is that right? yeah that will make less fluid if it become more saturated membrane is less fluid if there's more cholesterol added, membranes are less fluid. It will make less fluid. Then another thing, okay let's suppose this is a container with lot of milk, Let's suppose this is a container with lot of milk. there's lot of milk inside right and there is a butter, Milk inside. There is the butter. you know butter float into you know butter Imagine here is the prawn sitting. Right? And you imagine, here is a frog sitting. Can you imagine? Can you imagine? I don't know how to make a frog. I don't know how. But anyway, this is a frog. Something like this is also present in the... Like this is also. cell membranes. You know there is a frog sitting on the butter and using that piece of butter as a personal raft to move and float on the milk. Let me tell you what goes on. Is that right? Something like that apparatus is also present here. Let me tell you what is that apparatus. Of course there is no frog there. Actually in some part of the cell membrane What really happens? that phospholipids are more tightly packed, more tightly packed and not only phospholipids are more tightly packed, their fatty acid components are longer the fatty acid components are longer and there are very tightly what is this cholesterol so in some part of the cell membrane there are some specialized structure like The cell membrane, there are some specialized structures like butter piece here, right? And specialized structure, butter piece here right and then they become normal structure Now in this specialized structure what is happening that fatty acids are more saturated and they're longer and this area is having unusually high concentration of cholesterol right this is like butter what is happening? This area is having unusually high concentration of cholesterol. This is like butter piece and this butter piece is moving in the membrane. piece and this butter piece is moving in the membrane. Membrane is like milk layer and this butter piece is moving and what is the frog? Frog are special type of proteins present over there. Right? For example there may be very special protein present over here. very special protein present over here what else is there? What is this? Can you tell me what is this? In your medical studies you will come across something like this again and again. We are going to study this again. These are special type of receptor proteins. These are special bind with a... Now let me tell you what is receptor. Receptors are special macromolecules which will bind with a... Okay, let me make a simple receptor. Okay let me make a simple receptor. Let's suppose this is a protein. Now listen, this is a protein and when this protein bind with a special type of substance, when this protein bind with a very special type of substance, I am buying protein under one egg size membrane. protein undergoes change and this component of protein alter. Again listen, if I'm a receptor, if I'm a receptor, I have one end outside the membrane, If you put piece of gold in my hand I have one end outside the membrane, another end inside the membrane. Is that right? If you put some piece of gold in my hand, I start telling you, yes I have received it. What does it mean? That I can bind the gold outside and I can give signal of reception inside. Is that right? So what I am doing? Is that right? I am a molecule. On one side I can bind a specific substance. So what I'm doing? On other side I can give the signal. I'm a leaper. signals and modify the biological system. Such molecules which can bind with one specific substance and then produce modification in the biological system such molecules are called receptors. Besides, I can bind a step. Bind with one hand and produce a shimmy in the bridge. So what are receptors? Receptors are macromolecules to which when a specific substance bind that specific substance may be hormone or that may be neurotransmitter or It signals to the biological system, or that may be a drug. So anything specific bind with the receptor, and this is our protein. receptor will give signal to the biological system and alter the function of the biological system. This is our protein, this black system is the protein of peptide chain, Is that right? Now actually what is this? This is also a receptor system. This is a protein, this black system is a protein or peptide chain which is acting as a receptor. which is acting as our receptor. Why I say it is acting as a receptor? Because why do i say it is acting as a receptor here it will receive the stimulus. Whenever this molecule bind here, this start moving the tail end and this will give signal into cell. For example this is epinephrine or norepinephrine. because see the bind here tail end f in f frame here This is the receptor of epinephrine or norepinephrine. When epinephrine bind here the receptors give intracellular signal. Why? Because epinephrine cannot enter into cell. Nefrin is highly polar compound it cannot enter into cell. So extracellular stimulus can bring intracellular response due to the presence of receptors in the cell membrane. Again let me tell you in the cell membrane attention please You know, someone comes to visit you, if he is decent enough and if he is not allowed to enter your home blindly, he should stand outside like a thorough gentleman outside your door and then he should push the, what? Door. bell and then there will be a train train train and inside your house some activity may change and you may rush to the door so what is doorbell doorbell is a receptor doorbell is a receptor that and who was the person who came and pushed the doorbell he was the neurotransmitter or hormone or drug when he bind with the receptor it gives signal inside the cell is that right so what are receptors receptors are macromolecules usually came and pushed the signal inside the sound is that right to which bind and bring the interest proteins to which a specific substance binds and bring the intracellular changes or bring the changes in the biological system. changes are being the changes in the biological system am i clear are lipids soluble and they can go into cells if a cell can go into a system let's suppose this Am I clear? Now let me tell you something interesting. Some substances are lipid soluble and they can go into cell. If a substance can go into a cell, its receptor should be present within the cell. Let me tell you, cell is under the influence of one molecule is thyroxine let's suppose this cell is under the influence of two hormones. One hormone is, one hormone molecule is thyroxine. Have you heard of thyroxine? Thyroxine is a very very small molecule and it can easily go into the cell. Right? Another hormone is Insulin. Let's suppose another hormone is Insulin. Insulin is a very large molecule with lot of amino acids. Now Thyroxine can go into cell. Insulin cannot enter into cell. So receptor for Thyroxine should be present inside the cell. And receptor for Insulin should be present outside the cell. which can be used for both on the cell membrane. Am I clear? So what I am really trying to tell you, I am trying to tell you all those substances which cannot enter into cell, for those substances receptors should be expressed on the cell membrane. of something... What is the function of the receptors, membrane receptors? They take the extracellular signal and produce intracellular responses. Take the extracellular signal and produce intracellular response. Is that right? Am I clear? No problem? Now of course whenever you see there is a hormone which is very large or highly polar, Of course, you see there is a hormone highly polar, its receptors should be on the surface. it will set us to be on the surface. Let's go back to our frog. We were talking about that in some specialized area of the cell membrane, The cell membrane is a little thick, cell membranes become little thick, as told tightly packed, phospholipids and cholesterol tightly packed and lipid fatty acids are very long and fully saturated. fatty acids are fully saturated, is that right? They are having special type of proteins attached and these proteins which are fixated on this act like a frog. Is that right? and they are having special type of proteins attached with them and these proteins which are fixated on this act like a frog they are riding over it and riding through it what are these these are receptors and They are riding over it and riding through it. What are these? These are receptors. there may be some receptor associated proteins also. And there may be some created proteins also. Maybe this is the receptor associated proteins. Maybe this is receptor as you take it, Now, whole this signal mechanism, protein. Now, all this signal mechanism, whole this signaling proteins along with this structure are called lipid rafts. all this signaling protein along with this structure. What are they called? Lipid raft. You know rafting, is it right? So we say receptors and their acid proteins are resting in the membrane in specialized area. So we say receptors and their associated proteins are rafting on the what? In the membrane in specialized area. Am I clear? No problem up to this? So what we have learned up to now about the phospholipid nature of the cell membrane and we have talked about that the lipid raft. Right so what we have learned up to now that we have talked about the phospholipid nature of the cell membrane and we have talked about that the lipid rafts present, we have talked about the fluidity and the factors which affect the fluidity. and the factor which affect the fluidity. Is that right? So break now, We have a break now then we'll talk about the proteins associated with the cell membrane. then we will talk about the proteins associated with the cell membrane. Right, in the very beginning of the lecture we said that cell membranes are made of phospholipids, cholesterol and associated proteins. Let's discuss associated proteins in little bit detail. Actually, all the proteins which are associated with the cell membranes can be primarily divided into two types of protein. Candy fried into two, One type of the proteins which pass through and through the membrane. For example this is a protein which is passing throughout the membrane right and there may be some proteins which are just you can say attached so you can fry them and... outside the membrane. or they are attached inside the membrane or these proteins may be hooked with the... They are, these proteins may be host to the, this particular protein is a protein which is passive. Now look... This red color protein is a protein which is passing through and through the membrane. Who out there, who wants to do that? And these green proteins are either present on internal side of the membrane or attached on the external side of the membrane. and these green proteins are either present on those proteins right those proteins which pass throughout the membrane those protein which pass throughout the membrane these proteins are called integral proteins what are they called integral which proteins So membranes have special type of integral proteins which are passing through the membrane and these integral proteins are also called transmembrane proteins. What are they called? Trans membrane. proteins. So integral protein, the transmembrane proteins are those proteins which pass through and through the membrane and they do have an extra cellular domain as well as they have an intracellular domain. is that right? so naturally and what about these proteins? the green proteins they are not passing through and through the membrane they are expressed either on external side of the membrane or they are expressed to the internal side of the membrane and these proteins are called simply peripheral proteins because they are on the peripheral sides of the membrane so they are called yes please peripheral proteins. So peripheral proteins are loosely attached with the membrane. They are loosely attached with the membrane and they may be attached to an external side of the membrane or internal side of the membrane and these peripheral proteins are attached with the membrane in a non-covalent ways. They are not covalently attached because if they are attached covalently then they will be strongly attached but they are non-covalently attached with the membrane. and they can be easily shaken away from the membrane. easily changing in the ionic composition changing the th They can be easily removed from the membrane. Just changing in the ionic composition or changing the pH, you can remove the peripheral proteins. But integral proteins are really the part of the membrane. Integral proteins, because they pass through and through the membrane, so if you really want to remove the integral protein, you need to remove the peripheral proteins. to disrupt the membrane. Am I clear? No problem. Now I will go into detail of integral proteins first of all. I am going to detail up and tell total proteins associated with the membranes make about 50% of the membrane component. Before I move forward the total proteins associated with the membranes make about 50% of Let us say that cell membrane protein and remaining 50% of the membrane component. So you can say that cell membranes are 50% proteins and remaining 50% has about 47% lipids and 3% carbohydrates. 7% lipid. Are you understanding me? You don't understand me. Okay. A cell membrane has proteins how much? 50% right and lipids are how much? How much? 30. Mostly phospholipids with some cholesterol and other lipids. about 47% mostly phospholipid with some cholesterol and other lipids and then there is carbohydrate And there is carbohydrates. Carbohydrates are only 3% of the mountain. Carbohydrates are only 3% with the membrane. Right? We have discussed about the lipids in detail. Now we are going to talk about proteins and then we'll talk about carbohydrates. About the proteins, I'm saying there are two types of proteins. There are integral protein then there are peripheral proteins. Is that right? Now I will go into detail of integral proteins. Right? What are the functions of an integral protein? Why integral proteins have to be there? in the membrane. They are very very important function number one. As I told you in the beginning that those substances which are highly polar or very large substance for example there is a polar compound even if it is small you know sodium it is a charge or calcium it is having charge or chloride it is having charge these substances cannot diffuse through the membrane or can they diffuse through the membrane or even potassium it is having or even put a needle in the middle of the membrane. a charge on it, it is not lipid soluble. Can it diffuse out through membrane? No. But when we need to move such substances which are not lipid soluble but we need to move through the membrane, We need to take a help. Teens can help move the substance through the membrane two ways. then we need to take a help of a protein. How the proteins can help us to move the substances through the membrane? there are two ways one way is that proteins make channels as I told you previously but let's suppose this is one peptide chain okay let's suppose here is this is one peptide chain There are some ways that teams make channels. I told you previously that let's suppose this is one mate here, Then I make here another peptide chain. and there is here, suppose, Then there is here another peptide chain. how many times... And in the end another peptide chain. Let's suppose how many peptide chains I have made here? 1, 2, 3, 4, 5. These are 5 amino acid chains or peptide chains. these are five peptide chains if you put them together they will make a channel they will make a channel are made If you put them together they will make a channel. They will make a channel and such channels are present in the... Cell membranes. These channels are made of what? of this place they are made of protein amino acids Carbohydrate, proteins or lipids? Yes please. These channels are made of proteins, amino acids. And in these channels, In these channels, this central area is full of what? this central area is full of what? Water. Water. This is having water filled This is having, call it aqueous tunnel. Central tunnel we call it aqueous tunnel the water can move through and through from this so many water soluble substances can pass through the channels The water can move through and through from this. So many water soluble substances can pass through the channel. Is that right? So what did I tell you? So what did I tell you? That one type of integral protein is whole group of integral protein is working as channels and these channels can help the substances to move across the membrane. A whole group of integral proteins is working as and these channels lift the muscles to move across the one function. This is one type of integral, Then another integral protein. one function of integral protein. Then another integral protein. I don't know how to make bird but some proteins are this is another integral protein which is present through and through what membrane This is another brain. It can catch. what it is doing it can catch a substance here You catch that substance here. It will catch that substance here and as soon as a substance binds with it, it moves through that and release the substance in. moves to that let me so what Let me show then what it will do. So what has happened to this protein? has happened to this This protein has altered its structure. Such alteration in protein structure is called, It's structure, such alteration in protein structure is called, it is called transformation. There are some proteins undergo some transformation when they bind with the substance, it is called formation. And it takes the substance, right. And the mouth of this protein will take the substance carries the substance inside. carry the substance inside. These proteins are not having the central... Such proteins are not having the central water channel. So these are not channels. These are simply called as a group. These proteins are called carrier protein. They carry a substance undergo some change and shift the substance across the membrane. Is that right? But they are very specific. Some carriers are only for one substance, the other carriers which are only for other substances, the specific what they will transfer. So this is second type of integral protein. So some integral proteins are working as channels, the other integral proteins which are working as carrier proteins, they are working as yes please carrier proteins. you understand why these proteins must be present in the membrane? because cell has to take lot of substances inside or whatever it has synthesized it may need to release them out. is that right? so these are carriers, carrier proteins right then there is another group of course this beautiful design should be there also okay so these were channels these are carrier proteins then there are some other proteins so these are your proteins proteins also also which are present throughout the membrane right and these proteins even though they are through and through the membrane they can get a substance bind a substance A plus B with them and then release them as a plus b with them and then release them C plus D. what is this protein? enzyme you know this is the metabolic function of enzyme they can take one substance and convert into another substance or enzymes facilitate a what biochemical reaction so there are some enzymes which as c plus what is this they can take one for thousand convert to silly data are present within the within the cell membranes right of course some enzymes are attached outside or inside if enzymes are attached on the external aspect of the membrane and Right? Of course. Through and through the membrane, or internal aspect of the membrane then enzymes are there as peripheral protein. and then they are going to... But some enzymes are present through and through the membrane and then they are considered as component of integral proteins. Simple, simple biological barrier. So what we are talking about, They are dynamic functions. membranes are not just simple biological barriers, they are dynamic functionally, right. They are having channels, They are having sputter carrier, they are having transporter carriers, carrier proteins, carrier proteins. they are having enzymes as integral proteins, They are having enzymes as integral proteins. right. What else membranes can have? Anyone who can tell me? They are having special linker proteins. They are having special linker proteins. Look at this monkey. This is another integral protein. This is another integration. Its hands are dangling out and legs are dangling in. What it is doing there? There is a protein which is present outside the cells. Outside, maybe this protein is holding some special type of, suppose, collagen. Do you know collagen? Outside, Collagen is a protein which is present outside the cells and inside there may be actin. there may be actin. It is sticky to the skin. It is sticky to some filaments called actin. So what it is doing? It is attaching this part of the cell with extracellular environment but it is just structurally fixating it. It is attaching this part of the cell with extracellular and virtually fixating it. You are understanding it? What is the advantage of this? You are understanding it? That this is a molecule which is molecule of a protein which is transmembrane and it bind the internal cytoskeleton with extracellular component and This is a molecule which is molecule of a protein which is internal cytoskeleton with extracellular component. help the cell for a structural stability. Structural stability. Are you understanding? Are you understanding? Different cells in different tissues need to be structurally attached. Different cells in different tissues need to be structurally attached. Right? Right? And different cells have different shape. And different cells have different shapes. Now, this is intracellular proteins. This is intracellular protein which are also called cytoskeleton. which are also called cytoskeleton. As you have bones, As you have bones, you know you are having bone, you know you are having bones, I think you are sure. I think you are sure. Bones help you in many things including giving you a shape and strength. ...won't help you in many things including giving you a shape and strength. Is that right? In the same way as you have skeleton, Is that right? cells also have In the same way, Skeleton. cells also have skeletons. These are skeleton proteins, These are skeleton proteins of the cell. skeletal proteins of the cells. As a group these proteins are called cytoskeleton. So cell membrane inside has cytoskeleton. There are many many cytoskeleton proteins. And outside there are extracellular, collagen and other proteins. Right, to stabilize the internal cytoskeleton with external extracellular matrix. We use the term for this extracellular matrix. We need some types of proteins which are what? Trans membrane integral. On one side they can hold the extracellular. Components in other side they should be able to hold the intracellular cytoskeleton. And these proteins are also example of what type of proteins? Yes. What type of proteins? Integral proteins. Is that right? So how many functions of integral proteins you have seen? The integral proteins may be acting as channels, they may be acting as carrier proteins, Yes, ma'am. they may be acting as enzymes, they may be acting as... enzymes and of course they may be acting as what is this? linker protein. they are link they are producing a link between intracellular protein and extracellular proteins. linker proteins. right? linker's protein. then integral proteins have one very important function. one more what is that? okay let's suppose this is a protein which is present throughout the membrane and This protein has extracellular component, it has transmembrane component and intracellular component. Is that right? Let us suppose this protein can bind the insulin. When insulin come, insulin binds over here. when insulin binds over here right it start giving signals inside so this protein is working as receptor so receptors in the membranes are also integral proteins So today onward remember cell membranes are made of phospholipids and associated proteins. Associated proteins may be integral proteins or peripheral proteins. Integral proteins are transmembrane protein or through and through protein. Integral proteins have many functions. They may be functioning as channels, they may be functioning as carrier proteins, they may be functioning as enzymes, they may be functioning as linker proteins, they may be functioning as receptors. Is that right? Broadly, broad main categories of, functional categories of integral proteins. And about peripheral proteins, peripheral proteins, as I told you, they are attached to the external. aspect of the cell membrane or internal aspect of the cell membrane and peripheral proteins are loosely attached or non covalently attached and they are held with the membrane only with the weak very weak electrostatic very unique static forces can be disrupted very easily away from the forces so they can be disrupted very easily away from the membrane the peripheral proteins right and peripheral proteins are basically acting as functionally acting as cytoskeleton sometimes what happen look here inside the cell at this point some proteins are attached like this right or here are some proteins end proteins basically acting as cytoskeleton in the... and they are stabilizing the structure of the cell. Now these protein flamants are attached with the internal aspect of the cell. Right? So they are transmembrane or they are integral or they are peripheral. proteins? the peripheral proteins. so many of the peripheral proteins which are attached to the inner aspect of the membrane they are component of the cytoskeleton. they are the component of the cytoskeleton. Even though I told you cytoskeleton protein which is peripheral protein may be associated with linker protein. Even though I told you cytoskeleton protein which is peripheral protein may be associated with linker protein. It may be associated with linker protein which may link the cytoskeletal peripheral protein with extracellular matrix. It may be associated with linker protein which may link the skeletal peripheral protein with extracellular. Am I clear? Then another important relationship or function of the peripheral protein is, Then relationship or function of the... listen, some of the peripheral protein are working with the receptor. Let me tell you how. Let's suppose here is a receptor. and this receptor protein passes 7 times through the membrane. Such receptor which peptide chain passes 7 times, they are called 7-pass receptors. Now 7-pass receptors are integral protein. You are understanding it? But it may be associated with some other proteins which are attached with it inside. You are understanding? This is a receptor. Receptor is an integral protein. But when receptor is activated, it gives signal to some protein which is associated inside. This protein which is associated inside, This protein which is associated inside, what is this? this protein may produce, This is an example of peripheral protein so integral proteins may be associated with peripheral protein and this protein may produce let's suppose this protein may give signals further into cell right and activate second let's suppose, this protein may give signal further into the cell, right? And activate second messenger system. Next messenger will activate. messenger system messenger system actually let me tell you suppose the hormone which come here that is the first messenger Right, when hormone come to a cell that is first messenger. First messenger work with the receptor. Receptor activate some other intracellular protein and intracellular protein produce second messenger. So in some books they say proteins related with second messenger system are also peripheral proteins. The point which I wanted to tell you that proteins which are associated with the second messenger system they are not integral proteins they are peripheral protein but receptors are integral proteins. That's right. Any question up to this? Any questions up to this? Okay, we will discuss further detail tomorrow. Okay, we'll discuss.

So let's talk about the structure of a cell membrane. Let's suppose here is a cell Suppose we take a typical cell here, right? Now all of you know that cell has a basic structure, it has a nucleus and there is cytoplasm and it is surrounded by the cell membrane, There is sight of detail. right? into detail of the structure of the cell membrane.

Primarily cell membrane is made of phospholipids and associated proteins. Again what are the basic two components of cell membrane? This is made of phospholipids and associated proteins. Is that right?

Now, let me draw this structure right in detail. Basically, this cell membrane is a double layer of the molecules. Primarily it is a double layer of molecule.

Because it is double layer of a layer of molecules, so it is also called lipid biome. layer because it has lot of lipid and it's a double layer of the molecule it is also called lipid by layer. Now let me draw a component of it.

There. The basic component. Suppose this is a cell and I just draw cell membrane in detail from this point up to this point only right first of all the basic component is phospholipid now phospholipids are what phospholipids are having one part which is polar right this is the polar part of the phospholipid here there is phosphate and with that it is having fatty The cells have the acid. acids. What is it?

fatty acids. This is the basic molecule which is going to make cell membrane. What is it? Acid.

This is the basic molecule. So in the cell membrane there are phospholipids and it has one polar compound, It has one acid. See how a lot of the cells make the cells.

polar end and other are fatty acids. Right? Now we have to see how lot of these molecules make the cell membrane. Before we go, how do you... Before we go how these molecules are oriented you must know that extracellular environment is aqueous environment.

There is a lot of water outside the cell, outside the cell membrane and there is lot of water inside the cell membrane. So it means extracellular environment is aqueous. So it means it was, Aqueous environment.

And intracellular environment is also aqueous. Is that right? There is water outside the cell and there is lot of water inside the cell. it was, So it means this cell membrane is separating extracellular aqueous environment from the, it was, it was, yes. yes, intracellular aqueous environment.

Is that right? The polar comes polar, Now, you must be knowing that polar compounds dissolve into polar compound. Thank you.

Right? This is polar component of the phospholipid. these two fatty acids, Because this is polar, it has some charge.

It is water soluble end of the molecule. these are not... And these two fatty acids, these are not water soluble.

These fatty acids are not water soluble. of the molecule which is water soluble it is called hydrophilic. What is this component called?

hydrophilic. And this component which does not dissolve in water this is called hydrophilic. So we can say phospholipid molecule have hydrophilic component, they have a head which is hydrophilic and they are having tails which are hydrophobic. Is that right?

Now what really happens that in this part of the membrane, this water soluble part will be oriented outward towards the head. right and what are here these are yes please fatty acids and these are hydrophobic is that right now actually this is one layer other layer will be on this side layer of the molecules now you can see that cell membrane is made of double layer of phospholipids right Made of double chondromal. I have shown you the molecular structure of the cell membrane.

Now, Now question is that why these molecules of phospholipid are oriented in such a fashion? that is oriented in such a fashion. Answer is very simple. Answer is very simple.

You know these component fatty acids they are not going to dissolve into water. You know these components fatty acids they are going to dissolve into water. They avoid water.

They are hydrophobic. So it means this water outside and water inside. They avoid they are hydro.

So outer layer of the molecule this hydrophobic component will be directed away from the water and in inner layer again these fatty acids will be directed away from the water so they will be directed towards each other is that right This water outside in inner layer again these fatty acids will be directed away from the water. So they will be directed towards each other. So what we can really see that fatty acids right they dissolve into each other. See that acid, right, they dissolve into each other.

They attach with each other. They attach with each other. They are oriented towards each other. They are oriented towards each other.

Just like you put a drop of oil and another drop of oil in the water. Just like you put a drop of oil and another drop of oil in the water. Oil drops will fuse with each other.

Oil drops will fuse with each other. You take a little bit of water put two drops of oils. You take a little bit of water, put two drops of oil. Eventually what will happen to those drops of oil? Eventually what will happen to those drops of oils?

Oil dissolve into oil. Oil dissolves into acid, Is that right? In the same way is water right? The same way, the side...

outside, water inside and this is something like oil, inside this is something like oil fatty acid so they are oriented towards each other and they make the central portion of the cell membrane these blue parts right this is charged part or polar part or hydrophilic part hydrophilic means water fatty acids. So they are oriented towards each other and they make the central portion of the cell membrane. But as you know these blue parts right of the phospholipids this is charged part or polar part or hydrophilic part. Hydrophilic means water loving part.

This component is also water loving. This component is also water loving. So fatty acids which are in the outer component they are So fatty acids which are in the outer component their fluid part will be oriented outward.

what is this? hydrophilic part will be oriented outward and phospholipids which are inside inner side of the membrane their hydrophilic component will be directed towards the inner side. And phospholipids which are inside inner side of the membrane directed towards the inner side.

So what really happened that cell membranes are made of double layers of phospholipids and phospholipid molecules are oriented in such a way that in So water is made of double layers of phospho. oriented in such a way that in each layer fatty acids are directed towards each other and fillet, each layer fatty acids are directed towards each other and hydrophilic polar components of phospholipids are directed towards the external environment, polar components of our lipids are directed towards this. aqueous environment or they are oriented towards the internal aqueous environment.

Am I clear? This is the very basic structure. We have not talked about the associated proteins. Now another thing, you see the core of the cell membrane You see the core of the cell membrane is having lot of lipid inside. is having lot of lipid inside.

What is this? This is all lipid. So it means those compounds which are highly charged or those compounds which are very large, That means those compounds which are very large, can they directly? can they directly enter into cell? No.

Only those things can enter. No, because only those things can enter, cross this membrane which are lipid soluble. You know core of the membrane is made by the lipid. Is that right?

So if there is some substance here which is lipid soluble, So if there is some substance here which is lipid soluble, it can dissolve into membrane and come in. it can dissolve into membrane and condiment. Or there is any other substance which is lipid soluble inside, Any other substance which is lipid, it can dissolve into membrane and go out. it can dissolve into membrane. Right?

So which substances can cross the cell membrane easily? So which substance easily? Which substance we can cross in easily?

Which substances can cross the cell membrane easily? Substances which are lipid soluble and substances which are very small molecular weight. Substances which are lipid soluble and substances which are very small molecular weight, So we can say that... right?

So we can say the substances which are lipid soluble or substances with very very small yes molecular weight, Yes, this is going to go out. these substances can directly go into the cell or if these substances are inside they can easily go out Why? Because they can dissolve into lipid and pass through that. they can dissolve having charges But other substances which are larger molecules or those substances which are highly polar.

Polar substances mean which are having charges on them. For example, this is another substance and this substance or molecule is having charges on it. on it it's a polar compound.

Can it dissolve into lipid? So can it enter directly into cell? Can it enter? No. So it will be repelled away.

In the same way let's suppose this is another compound and this is very very large compound. same way let's go can If it's very large compound can it dissolve into lipid and can it go out? No. What does it mean then?

It means that this lipid component of the membrane is providing the permeability barrier for the large compounds and for the highly polar compounds that they cannot pass through membrane. it dissolve me It means if some very large molecule has to come in or and we'll have to move through any large molecule or polar or charged molecule has to move through the membrane it has to have some special facility to pass through the membrane. Let me repeat it.

I just said up to now that cell membrane is made of lipid bilayer primarily and associated proteins, the routine that is right. Proteins I did not discuss up to now. And in lipid bilayer what is happening mainly it is consisting of phospholipids. mainly it is a tail guard for fatty acid and polar head size it Is that right? And phospholipids are having the polar heads and and hydrophobic tails.

Hydrophobic tails or fatty acids are oriented towards each other and polar heads of the molecule are either outside towards extracellular aqueous environment or oriented inside to was a core of cell membrane the intracellular aqueous environment. So core of the cell membrane is made of primarily lipids, right. And those substances which are lipid soluble or very small molecular weight, It means they have to pass through the membrane.

they can easily pass through the cell membrane. But other substances which are very large molecule or which are having lot of charge on the molecule, We need special arrangement. they cannot pass through the membrane by simple diffusion. Is that right?

It means for such substances if they have to pass through the membrane, we need special arrangement. There should be special windows and there should be doors through which these membrane can slip in or out. membrane can slip in or out those special windows or doors within the male dosage component proteins in the cell membrane there are special type of proteins is that right and those proteins you hear that here is a protein Those special windows or doors should be made of such material.

within the cell membrane are made of which component? Proteins. In the cell membrane there are special type of proteins is that right and those proteins for example let me tell you here that here is a protein and let's suppose okay This is a protein molecule made of multiple peptide chains and these peptide chains, Let's suppose protein molecule made of multiple peptide chains and these peptide chains, suppose this is one peptide chain, this is second, this is third, this is four, so this is one peptide chain, right? And these peptide chains are arranged in such a way that this is second, this is third, this is fourth, right? And these peptide chains are arranged in such a way that there is a lock.

In the center of this molecule, right, there is a longitudinal tunnel. This is a tunnel. This is a tunnel and this is water filled tunnel. And this is water filled tunnel.

What is it? Water filled tunnel. What is it?

We call it aqueous channel. Water filled aqueous channel. What is it?

this channel? this channel has a hole which is full of water and then those substances which are water soluble they can pass through this. What is this channel? This channel has a hole which is full of water and then those substances which are water soluble they can pass through association with the cell membrane.

so this is one way one of the function of the proteins that proteins are present in association with the cell membrane phospholipid so that substances are allowed to pass in and out. Such type of proteins which are present in the cell membrane, The type of proteins which are present in the cell members, they are called channels. What are these called? channels and I will tell you the functions of proteins, they are called channels.

And I will tell you about proteins, more functions of proteins later. more functions of proteins later. Let's come back to this component. Let's come back to this component, After that I will go into detail of the protein. detail of the protein.

Another thing, the types of fatty acids and phospholipids which are in outer leaflet and which are in the inner leaflet, The type of fatty acids, phospholipids. which are in outer leaflets and which are in the inner leaflets, they are not identical. they are not identical. I will go to the proteins in detail. later again listen you know this is the outer leaflet of the cell membrane and this is the inner leaflet of the cell membrane now these phospholipids which are present in outer leaflet This is the spray which is produced for the picture effect slightly different than the phospholipids which are present in inner leaflet.

It means phospholipids of outer leaflet and inner leaflet are not identical. So it means outer leaflet phospholipid structure and inner leaflet phospholipid structure is not symmetrical. trickle. They are having asymmetry. What we call this term asymmetry.

Asymmetric, Now which are the phospholipids which are present in outer part of the cell membrane? asymmetric, outer part of the dial choline, ok I will write it before you start crying, Number one, these are phosphatidylcholine. Okay, I will write it before you start crying. phosphatidylcholine this is a type of phospholipid right phosphatidylcholine this is present abundantly in the outer reflect right choline, type of papal lipid.

this is present abundantly in the outer reflex with it there is another friend so fingo myelin so first part it has cooling and fingo myelin are two types with it there is another friend phospholipid which is called sulfingomyelin sulfingomyelin Myelin. So phosphatidylcholine and sphingomyelin are two type of special phospholipids which are abundantly present in the outer leaflet of the cell membrane. of These are the two phospholipids.

Right? Yes, These are the two phospholipids which are present in the yes please? please. Phospholipids which are specially present.

outer leaflet. Now we'll talk about what Again, there are two important phospholipids which are abundantly present in the inner leaflet of the cell. phospholipids which are specially present in inner leaflet right again there are two important phospholipids which are abundantly present in the inner leaflet of the cell membrane one is phosphatidylethanolamine One is phospholipid.

Asparti Dial I don't know who was man who was putting the names of these put simple name like Carla, Ethylamine It is thick man Joanne I don't know he's sick man who put these names right so the inner part of the cell membrane it is having some funny type of you can say phospholipid phosphatidyl ethanolamine So the inner part of the cell membrane It is having some funny type of Asparti Dial di-dial okay ethanol main right this is one and the second type of phospholipid which is abundantly present in inner part of the inner leaflet of the cell membrane that is called phosphatidylserine phosphatidylserine Right? So because phospholipids in outer part are somewhat different and phospholipids which are present in inner part of the membrane they are slightly different. So we can say that cell membrane outer leaflet and inner leaflet show some degree of asymmetry.

show some degree of asymmetry. They are showing some degree of asymmetry. Later on we will learn that another asymmetry that the proteins which are the outer part different proteins which are attached to the Right.. Later on we will learn that another component add to the asymmetry that the proteins which are attached to the outer part are slightly different than the proteins which are attached to the inner part.

so not only So not only difference of phospholipid make the asymmetrical situation, Make the asymmetrical situation. Later on we will learn the proteins which are attached to the outer part of the leaflet and the proteins which are attached to the inner part of the leaflet are slightly different from each other. later on we'll learn the proteins which are attached to the outer part of the leaflet and the proteins which are attached to the inner part of the leaflet they are slightly different from each other.

each other so they also contribute to the asymmetric situation. So they also contribute to the asymmetric situation. And still later on we will learn that outer leaflet has lot of carbohydrates attached with it. Still later on we will learn the outer leaflet has a lot of hydrates attached. Inner leaflet does not have any significant carbohydrates.

But inner leaflet does not have any significant carbohydrate. So it means outer leaflet is having lot of carbohydrate molecules outside, This outer leaflet is having lot of carbohydrate molecules outside. inner leaflet does not have carbohydrate molecules. Inner leaflet does not have carbohydrate molecules. Again this difference of carbohydrates applied on this leaflet also Again, adds to the asymmetry of the inner and outer leaflet of cell membranes.

the difference of carbohydrates applied on this leaflet also at asymmetry of the... I think I need to recap this. I was trying to put a concept in your mind that cell membrane is made of phospholipid bilayer with associated proteins.

Is that right? and it is making outer leaflet and inner leaflet and outer leaflet and inner leaflet are not identical. If they were identical, we could say that they are symmetrical but they are not symmetrical. why they are not symmetrical?

there are multiple reason. one reason is that phospholipid in outer leaflet are different and phospholipid in inner leaflets are different. second reason the protein associated with outer leaflet are different.

leaflet are different and protein associated with inner leaflet are different. Third reason outer leaflet has lot of carbohydrates attached outside but inner leaflet does not have any carbohydrates attached inside. So all these reasons make the outer and the inner leaflet of the cell membrane asymmetrical or non-identical to each other.

Ace Metric Lift Anyone who does not clean these works Am I really clear? Anyone who does not understand? Raise your hand, I will run away. Everyone understand?

That's good, we can continue. Another thing, in between, in between the legs of these what? Fatty acids, there is some naughty molecule here. It loves to be here. I don't know why.

Who knows this naughty molecule? Yeah. Anyone please use your own head. Anyone please use your own head.

This is a very special type of lipid. Okay let me tell you I will draw that structure in a large way right and there are their beautiful legs. okay it's little bit I should say having a dancing tendency. Now yeah what are these?

these are polar ants right water soluble ants and these are lipid soluble and there are some molecules which love to be here you know naughty type Who will tell me what are these molecules? You know it, I'm sure you know the name of these molecules. We call them cholesterol.

Have you heard of cholesterol? So cholesterol is another type of lipid which is present in the cell membrane intercalated in between the legs of the phospholipids. The inter between the legs of the most of the cholesterol molecule is lipid soluble.

Is that right? And cholesterol molecule have hydroxyl. This is a Hydroxyl ends are oriented outward.

Why? Hydroxyls are polar end. It is oriented inward.

So most of the cholesterol molecule is lipid soluble. But their hydroxyl and their polar of charge, So it is oriented inward. But their hydroxyl ends which are polar or charged, they are oriented outward.

they are oriented outward. Is that right? We have learned that cell membrane most important lipids are phospholipids but they do have a small percentage of troll molecules in phospholipids.

that cell membrane most important lipids are phospholipid but they do have a small percentage of cholesterol molecules intercalated in between the phospholipids. Is that right? Is that right? Any question up to this?

Any question up to this? There is no. Very interesting. Another thing very interesting These phospholipid molecules... These phospholipid molecules are really not fixed.

They are not fixed. For example, For example, this molecule is present here. this figure is present here.

You look around and that may slip on other side. You look around and that is a slip on other side. What does it mean?

All these molecules are mobile. Phospholipid molecules are mobile. They keep on moving laterally.

They keep on moving laterally. Is that right? Is that right? They are not fixated in their position. They are not fixated in their position and they display the lateral.

These phospholipid molecules are mobile. not fixated in their position and they display the lateral movement and this concept of lateral movement is called fluidity of the membrane. movement and this concept of fluidity of the membrane molecules are like a fluid area they are mobile they are not fixed in position is that right so phospholipid molecule they can slip laterally property The membrane molecules are like a fluid. and in a fluid area they are mobile.

They are not fixed in a particular specific position. Is that right? So phospholipid molecule along with cholesterol they can slip laterally right? And we say that membrane shows the property of fluidity. of fluidity property of yes Property of?

Yes? Fluidity. This is an important property.

fluidity you know why it is so important to know that membranes have some fluidity because later which you will learn right sometimes cell has synthesized some let's suppose cell has synthesized a hormone now hormone is hormone molecules are packed into a membrane membrane bound vesicle this vesicle may come and fuse with the membrane. It may fuse with the membrane and these substances may go out. You know many cells secrete substances.

For example cells in the pancreas, There will be insulin containing vegetables. beta cell of the pancreas secrete insulin. So within, These vegetables are membrane bound.

if it is a pancreatic cell, there will be insulin containing vesicle and these vesicles that Insulin is going to be released. membrane bound and when insulin is going to be released this vesicle will float move towards the membrane and membrane of the vesicle will fuse with the cell membrane and where they fuse a small puncture point is made and insulin will go out and This moves towards the membrane and membrane to diffuse with the insulin will go out. then due to fluidity it will seal it will be completely closed is that right It will seal, it will completely close.

If this was a fixed membrane, If this was a fixed membrane, can it easily go out? No. So this process is called exocytosis.

this process is hydrophilic. The cell is showing exocytosis. So, it's fluid, it is important.

So if fluid it is important so that cell can show exocytosis. Sometimes cells are in a mood to eat something. In a mood to eat something, Let's suppose here happen to be a bacteria. let's suppose there happen to be a bacteria.

Right, this is very sad. You know why? Because cell is going to eat this bacteria if this is a white blood cell. Cell is going to eat this bacteria. Now this is a membrane of the white blood cell, This is a white blood cell.

right, and it has produced, catch the bacteria and then this membrane will progressively move to each other and then eventually it will fuse and this will go inside. It has produced a catty of food which has fused. And this will go inside.

This process is called endocytosis. What is it called? Again because membranes are fluid, Endocytosis. Again because membranes are fluid.

So during the endocytosis a piece of membrane has invaginated and then pushed off, so during the endocytogenesis, right. Still there is no hole in the membrane or will there be any hole in the membrane? the purple liquid comes on the side.

There'll be no hole because as soon as it remove away, The same way when this membrane... phospholipid come on the side and seal it. Is that right?

In the same way when this membrane from inside going out these phospholipids are added to the membrane. These fossil lipids are added to the membrane. So for the process of exocytosis or for the process of endocytosis membranes must have some degree of fluidity right and then this type of So for the right and this type of membrane biogenesis. what is this?

fluidity is also important for membrane biogenesis. Biogenesis means biogenesis means membrane synthesis. you know when cells are initially small when cells divide, You know when cells are initially small, when cells divide, daughter cell are small, daughter cell are small.

with the time cells keep on growing. with that cells keep on growing so it means their membranes should also grow. So it means their membranes should also grow. How the membranes grow? How the membranes grow?

So it means keep on inserting in the membrane. Cells synthesize new phospholipids and keep on inserting in the membrane and because membranes are fluid so keep on accommodating the new And because membranes are fluid, so keep on accommodating the new molecules and enlarging them. molecules and enlarging the surface area.

It means fluidity is important for alpha cytosis. So it means fluidity is important for exocytosis, it is important for endocytosis, it is important for membrane biogenesis, membrane yes biogenesis and fluidity is also right these are some important reasons why fluidity is important. Genesis, yes, fluidity is, right, these are some important reasons why fluidity is important, Now what are the factor which can alter the fluidity of the membrane?

For example if phospholipid molecules can more freely move we say membrane is more fluid and if the movement is relatively less free we say membrane is less fluid. fluidity of the membrane. We say membrane is more fluid and if the movement is relatively less free, Now do you know any factor which can alter the fluidity of the membrane?

we say membrane is less fluid. can alter fluidity? Temperature.

If temperature goes up, Do you know any? membrane will become less fluid or more fluid? It will become neat to explain it, Of course more fluid, there is no need to explain it, all of you must know.

all of you must know, temperature increases the movement of the molecules and molecules which are already ready to dance, they will dance more when temperature of the membrane goes up. So this is very easy, no need to remember it even. You don't need to remember the pressure.

That increasing temperature increases the fluidity of the membrane. Now another thing, Increasing the corolle content in the fluid, increasing the cholesterol content in the membrane, If we add more and more cholesterol in the membrane, it will increase or decrease. fluidity will increase or decrease? Very good. How do you know that?

Yes, very good. How you know that? yeah that's right he knows so well that when you are adding the cholesterol actually you know their legs cannot move now you know they're packed membrane components are more tightly packed when you insert the cholesterol you intercalate the cholesterol molecule in between the phospholipid molecules and membrane become less fluid.

So you can say adding the cholesterol make the membranes less fluid. Another thing you know these are the straight fatty acid and this is some what's wrong with this fatty acid yeah what is wrong with this fatty acid Yes, sir. It is having a kink in its leg. Can't you see it? You don't need to call I think Aristotle to discover this.

It is not straight, it is having a bend in it. Why it is having a bend? Some fracture there or what? Actually when fatty acids are saturated they are straight.

They are saturated, When they are unsaturated they have a kink. they are straight. Saturated, they have a kink. Study in biochemistry one day. you study in biochemistry one day right that's when fatty acids are fully saturated they are straight relatively straight chains and when fatty acids are unsaturated or relatively unsaturated they have bend in their structure Cateosols are fully saturated, they are straight, relatively straight kink.

And then cateosols are unsaturated or relatively unsaturated, then they're... not in their leg who told you they have legs and shoes no right now what is there they have a kink now what do you think Right now what is there? They have a kink.

What do you think? If in the membrane most of the fatty acid are unsaturated it means they are having If in the membrane most of the fatty acids are unsaturated, it means they are having bends. Bend. This will be more fluid or less fluid? This will be more fluid or less fluid?

More. That will be more. It will be more moving leg like this and this. Someone moving leg like this and this people tend to move away or move laterally. People tend to move away or move laterally.

So that really happens. So what really happens when fatty acids are relatively unsaturated membranes are more fluid. Is fatty acids valid in me? When you make the fatty acids more saturated and all fatty acids become straight, And when you make the fatty acids acid more saturated and all fatty acid become straight they become tightly packed membrane are less fluid am i clear no problem up to this right we have just talked about the fatty acids they become tightly packed, membrane are less.

No problem of today, we have just talked about the fatty acids, the cell membranes are made of double layer of phospholipids. the cell membrane are made of double layer of phosphor, lipid. Is that right? And polar ends of the phospholipids are oriented either outward or inward and hydrophobic fatty ends are oriented to each other.

and if polar ends of the fossil lipids are oriented either outward or in the opposite side, fatty ends are oriented to each other. Is that right? Yes, Matrika. Fatty acids in outer leaflets are different than proteins outside and only outer side has different properties.

Is that right? Then what did we discuss that this membranes are symmetrical or asymmetrical? They are asymmetrical because type of fatty acid in outer leaflet are different than the type of fatty acid in the inner leaflet.

So, if you have a fatty acid in the outer leaflets, it is not a fatty acid. It is a fatty acid. So, if you have a fatty acid in the outer leaflets, proteins outside and inside are different.

thirdly outer side has lot of carbohydrate inner side does not. it is is that right? then we talked about fluidity that phospholipid molecules can float around in the membrane so we say membranes show the characteristics of fluidity and why fluidity is important because there is processes of exocytosis going on there are phenomenon of endocytosis going on in the membranes and fluidity there are and then there's membrane then there's membrane biogenesis going on right so due to all these reasons it's very important and membrane should be appropriately fluid, is that right?

so that there are no fractures and punctures in the membrane, is that right? they should seal off. They should seal off. then we talked about that fluidity can be increased by temperature but decreased by adding cholesterol or making the fatty acids more saturated, Then we talked about fluidity can be increased by, but decreased by adding cholesterol or making the fatty acids more saturated. is that right?

yeah that will make less fluid if it become more saturated membrane is less fluid if there's more cholesterol added, membranes are less fluid. It will make less fluid. Then another thing, okay let's suppose this is a container with lot of milk, Let's suppose this is a container with lot of milk. there's lot of milk inside right and there is a butter, Milk inside. There is the butter.

you know butter float into you know butter Imagine here is the prawn sitting. Right? And you imagine, here is a frog sitting. Can you imagine?

Can you imagine? I don't know how to make a frog. I don't know how. But anyway, this is a frog.

Something like this is also present in the... Like this is also. cell membranes. You know there is a frog sitting on the butter and using that piece of butter as a personal raft to move and float on the milk.

Let me tell you what goes on. Is that right? Something like that apparatus is also present here. Let me tell you what is that apparatus. Of course there is no frog there.

Actually in some part of the cell membrane What really happens? that phospholipids are more tightly packed, more tightly packed and not only phospholipids are more tightly packed, their fatty acid components are longer the fatty acid components are longer and there are very tightly what is this cholesterol so in some part of the cell membrane there are some specialized structure like The cell membrane, there are some specialized structures like butter piece here, right? And specialized structure, butter piece here right and then they become normal structure Now in this specialized structure what is happening that fatty acids are more saturated and they're longer and this area is having unusually high concentration of cholesterol right this is like butter what is happening?

This area is having unusually high concentration of cholesterol. This is like butter piece and this butter piece is moving in the membrane. piece and this butter piece is moving in the membrane. Membrane is like milk layer and this butter piece is moving and what is the frog? Frog are special type of proteins present over there.

Right? For example there may be very special protein present over here. very special protein present over here what else is there? What is this?

Can you tell me what is this? In your medical studies you will come across something like this again and again. We are going to study this again.

These are special type of receptor proteins. These are special bind with a... Now let me tell you what is receptor.

Receptors are special macromolecules which will bind with a... Okay, let me make a simple receptor. Okay let me make a simple receptor.

Let's suppose this is a protein. Now listen, this is a protein and when this protein bind with a special type of substance, when this protein bind with a very special type of substance, I am buying protein under one egg size membrane. protein undergoes change and this component of protein alter. Again listen, if I'm a receptor, if I'm a receptor, I have one end outside the membrane, If you put piece of gold in my hand I have one end outside the membrane, another end inside the membrane.

Is that right? If you put some piece of gold in my hand, I start telling you, yes I have received it. What does it mean? That I can bind the gold outside and I can give signal of reception inside.

Is that right? So what I am doing? Is that right? I am a molecule. On one side I can bind a specific substance.

So what I'm doing? On other side I can give the signal. I'm a leaper. signals and modify the biological system.

Such molecules which can bind with one specific substance and then produce modification in the biological system such molecules are called receptors. Besides, I can bind a step. Bind with one hand and produce a shimmy in the bridge.

So what are receptors? Receptors are macromolecules to which when a specific substance bind that specific substance may be hormone or that may be neurotransmitter or It signals to the biological system, or that may be a drug. So anything specific bind with the receptor, and this is our protein. receptor will give signal to the biological system and alter the function of the biological system. This is our protein, this black system is the protein of peptide chain, Is that right?

Now actually what is this? This is also a receptor system. This is a protein, this black system is a protein or peptide chain which is acting as a receptor. which is acting as our receptor.

Why I say it is acting as a receptor? Because why do i say it is acting as a receptor here it will receive the stimulus. Whenever this molecule bind here, this start moving the tail end and this will give signal into cell. For example this is epinephrine or norepinephrine.

because see the bind here tail end f in f frame here This is the receptor of epinephrine or norepinephrine. When epinephrine bind here the receptors give intracellular signal. Why?

Because epinephrine cannot enter into cell. Nefrin is highly polar compound it cannot enter into cell. So extracellular stimulus can bring intracellular response due to the presence of receptors in the cell membrane.

Again let me tell you in the cell membrane attention please You know, someone comes to visit you, if he is decent enough and if he is not allowed to enter your home blindly, he should stand outside like a thorough gentleman outside your door and then he should push the, what? Door. bell and then there will be a train train train and inside your house some activity may change and you may rush to the door so what is doorbell doorbell is a receptor doorbell is a receptor that and who was the person who came and pushed the doorbell he was the neurotransmitter or hormone or drug when he bind with the receptor it gives signal inside the cell is that right so what are receptors receptors are macromolecules usually came and pushed the signal inside the sound is that right to which bind and bring the interest proteins to which a specific substance binds and bring the intracellular changes or bring the changes in the biological system. changes are being the changes in the biological system am i clear are lipids soluble and they can go into cells if a cell can go into a system let's suppose this Am I clear? Now let me tell you something interesting.

Some substances are lipid soluble and they can go into cell. If a substance can go into a cell, its receptor should be present within the cell. Let me tell you, cell is under the influence of one molecule is thyroxine let's suppose this cell is under the influence of two hormones. One hormone is, one hormone molecule is thyroxine. Have you heard of thyroxine?

Thyroxine is a very very small molecule and it can easily go into the cell. Right? Another hormone is Insulin.

Let's suppose another hormone is Insulin. Insulin is a very large molecule with lot of amino acids. Now Thyroxine can go into cell. Insulin cannot enter into cell.

So receptor for Thyroxine should be present inside the cell. And receptor for Insulin should be present outside the cell. which can be used for both on the cell membrane.

Am I clear? So what I am really trying to tell you, I am trying to tell you all those substances which cannot enter into cell, for those substances receptors should be expressed on the cell membrane. of something...

What is the function of the receptors, membrane receptors? They take the extracellular signal and produce intracellular responses. Take the extracellular signal and produce intracellular response.

Is that right? Am I clear? No problem?

Now of course whenever you see there is a hormone which is very large or highly polar, Of course, you see there is a hormone highly polar, its receptors should be on the surface. it will set us to be on the surface. Let's go back to our frog. We were talking about that in some specialized area of the cell membrane, The cell membrane is a little thick, cell membranes become little thick, as told tightly packed, phospholipids and cholesterol tightly packed and lipid fatty acids are very long and fully saturated.

fatty acids are fully saturated, is that right? They are having special type of proteins attached and these proteins which are fixated on this act like a frog. Is that right?

and they are having special type of proteins attached with them and these proteins which are fixated on this act like a frog they are riding over it and riding through it what are these these are receptors and They are riding over it and riding through it. What are these? These are receptors.

there may be some receptor associated proteins also. And there may be some created proteins also. Maybe this is the receptor associated proteins.

Maybe this is receptor as you take it, Now, whole this signal mechanism, protein. Now, all this signal mechanism, whole this signaling proteins along with this structure are called lipid rafts. all this signaling protein along with this structure. What are they called? Lipid raft.

You know rafting, is it right? So we say receptors and their acid proteins are resting in the membrane in specialized area. So we say receptors and their associated proteins are rafting on the what? In the membrane in specialized area.

Am I clear? No problem up to this? So what we have learned up to now about the phospholipid nature of the cell membrane and we have talked about that the lipid raft.

Right so what we have learned up to now that we have talked about the phospholipid nature of the cell membrane and we have talked about that the lipid rafts present, we have talked about the fluidity and the factors which affect the fluidity. and the factor which affect the fluidity. Is that right?

So break now, We have a break now then we'll talk about the proteins associated with the cell membrane. then we will talk about the proteins associated with the cell membrane. Right, in the very beginning of the lecture we said that cell membranes are made of phospholipids, cholesterol and associated proteins. Let's discuss associated proteins in little bit detail. Actually, all the proteins which are associated with the cell membranes can be primarily divided into two types of protein.

Candy fried into two, One type of the proteins which pass through and through the membrane. For example this is a protein which is passing throughout the membrane right and there may be some proteins which are just you can say attached so you can fry them and... outside the membrane. or they are attached inside the membrane or these proteins may be hooked with the...

They are, these proteins may be host to the, this particular protein is a protein which is passive. Now look... This red color protein is a protein which is passing through and through the membrane.

Who out there, who wants to do that? And these green proteins are either present on internal side of the membrane or attached on the external side of the membrane. and these green proteins are either present on those proteins right those proteins which pass throughout the membrane those protein which pass throughout the membrane these proteins are called integral proteins what are they called integral which proteins So membranes have special type of integral proteins which are passing through the membrane and these integral proteins are also called transmembrane proteins.

What are they called? Trans membrane. proteins. So integral protein, the transmembrane proteins are those proteins which pass through and through the membrane and they do have an extra cellular domain as well as they have an intracellular domain.

is that right? so naturally and what about these proteins? the green proteins they are not passing through and through the membrane they are expressed either on external side of the membrane or they are expressed to the internal side of the membrane and these proteins are called simply peripheral proteins because they are on the peripheral sides of the membrane so they are called yes please peripheral proteins. So peripheral proteins are loosely attached with the membrane. They are loosely attached with the membrane and they may be attached to an external side of the membrane or internal side of the membrane and these peripheral proteins are attached with the membrane in a non-covalent ways.

They are not covalently attached because if they are attached covalently then they will be strongly attached but they are non-covalently attached with the membrane. and they can be easily shaken away from the membrane. easily changing in the ionic composition changing the th They can be easily removed from the membrane.

Just changing in the ionic composition or changing the pH, you can remove the peripheral proteins. But integral proteins are really the part of the membrane. Integral proteins, because they pass through and through the membrane, so if you really want to remove the integral protein, you need to remove the peripheral proteins. to disrupt the membrane.

Am I clear? No problem. Now I will go into detail of integral proteins first of all.

I am going to detail up and tell total proteins associated with the membranes make about 50% of the membrane component. Before I move forward the total proteins associated with the membranes make about 50% of Let us say that cell membrane protein and remaining 50% of the membrane component. So you can say that cell membranes are 50% proteins and remaining 50% has about 47% lipids and 3% carbohydrates. 7% lipid. Are you understanding me?

You don't understand me. Okay. A cell membrane has proteins how much? 50% right and lipids are how much? How much?

30. Mostly phospholipids with some cholesterol and other lipids. about 47% mostly phospholipid with some cholesterol and other lipids and then there is carbohydrate And there is carbohydrates. Carbohydrates are only 3% of the mountain. Carbohydrates are only 3% with the membrane.

Right? We have discussed about the lipids in detail. Now we are going to talk about proteins and then we'll talk about carbohydrates.

About the proteins, I'm saying there are two types of proteins. There are integral protein then there are peripheral proteins. Is that right? Now I will go into detail of integral proteins.

Right? What are the functions of an integral protein? Why integral proteins have to be there?

in the membrane. They are very very important function number one. As I told you in the beginning that those substances which are highly polar or very large substance for example there is a polar compound even if it is small you know sodium it is a charge or calcium it is having charge or chloride it is having charge these substances cannot diffuse through the membrane or can they diffuse through the membrane or even potassium it is having or even put a needle in the middle of the membrane.

a charge on it, it is not lipid soluble. Can it diffuse out through membrane? No.

But when we need to move such substances which are not lipid soluble but we need to move through the membrane, We need to take a help. Teens can help move the substance through the membrane two ways. then we need to take a help of a protein.

How the proteins can help us to move the substances through the membrane? there are two ways one way is that proteins make channels as I told you previously but let's suppose this is one peptide chain okay let's suppose here is this is one peptide chain There are some ways that teams make channels. I told you previously that let's suppose this is one mate here, Then I make here another peptide chain.

and there is here, suppose, Then there is here another peptide chain. how many times... And in the end another peptide chain.

Let's suppose how many peptide chains I have made here? 1, 2, 3, 4, 5. These are 5 amino acid chains or peptide chains. these are five peptide chains if you put them together they will make a channel they will make a channel are made If you put them together they will make a channel. They will make a channel and such channels are present in the... Cell membranes.

These channels are made of what? of this place they are made of protein amino acids Carbohydrate, proteins or lipids? Yes please.

These channels are made of proteins, amino acids. And in these channels, In these channels, this central area is full of what? this central area is full of what?

Water. Water. This is having water filled This is having, call it aqueous tunnel. Central tunnel we call it aqueous tunnel the water can move through and through from this so many water soluble substances can pass through the channels The water can move through and through from this.

So many water soluble substances can pass through the channel. Is that right? So what did I tell you? So what did I tell you? That one type of integral protein is whole group of integral protein is working as channels and these channels can help the substances to move across the membrane.

A whole group of integral proteins is working as and these channels lift the muscles to move across the one function. This is one type of integral, Then another integral protein. one function of integral protein.

Then another integral protein. I don't know how to make bird but some proteins are this is another integral protein which is present through and through what membrane This is another brain. It can catch. what it is doing it can catch a substance here You catch that substance here.

It will catch that substance here and as soon as a substance binds with it, it moves through that and release the substance in. moves to that let me so what Let me show then what it will do. So what has happened to this protein? has happened to this This protein has altered its structure. Such alteration in protein structure is called, It's structure, such alteration in protein structure is called, it is called transformation.

There are some proteins undergo some transformation when they bind with the substance, it is called formation. And it takes the substance, right. And the mouth of this protein will take the substance carries the substance inside. carry the substance inside.

These proteins are not having the central... Such proteins are not having the central water channel. So these are not channels. These are simply called as a group.

These proteins are called carrier protein. They carry a substance undergo some change and shift the substance across the membrane. Is that right? But they are very specific. Some carriers are only for one substance, the other carriers which are only for other substances, the specific what they will transfer.

So this is second type of integral protein. So some integral proteins are working as channels, the other integral proteins which are working as carrier proteins, they are working as yes please carrier proteins. you understand why these proteins must be present in the membrane? because cell has to take lot of substances inside or whatever it has synthesized it may need to release them out.

is that right? so these are carriers, carrier proteins right then there is another group of course this beautiful design should be there also okay so these were channels these are carrier proteins then there are some other proteins so these are your proteins proteins also also which are present throughout the membrane right and these proteins even though they are through and through the membrane they can get a substance bind a substance A plus B with them and then release them as a plus b with them and then release them C plus D. what is this protein? enzyme you know this is the metabolic function of enzyme they can take one substance and convert into another substance or enzymes facilitate a what biochemical reaction so there are some enzymes which as c plus what is this they can take one for thousand convert to silly data are present within the within the cell membranes right of course some enzymes are attached outside or inside if enzymes are attached on the external aspect of the membrane and Right?

Of course. Through and through the membrane, or internal aspect of the membrane then enzymes are there as peripheral protein. and then they are going to...

But some enzymes are present through and through the membrane and then they are considered as component of integral proteins. Simple, simple biological barrier. So what we are talking about, They are dynamic functions. membranes are not just simple biological barriers, they are dynamic functionally, right. They are having channels, They are having sputter carrier, they are having transporter carriers, carrier proteins, carrier proteins.

they are having enzymes as integral proteins, They are having enzymes as integral proteins. right. What else membranes can have? Anyone who can tell me?

They are having special linker proteins. They are having special linker proteins. Look at this monkey. This is another integral protein. This is another integration.

Its hands are dangling out and legs are dangling in. What it is doing there? There is a protein which is present outside the cells.

Outside, maybe this protein is holding some special type of, suppose, collagen. Do you know collagen? Outside, Collagen is a protein which is present outside the cells and inside there may be actin.

there may be actin. It is sticky to the skin. It is sticky to some filaments called actin.

So what it is doing? It is attaching this part of the cell with extracellular environment but it is just structurally fixating it. It is attaching this part of the cell with extracellular and virtually fixating it.

You are understanding it? What is the advantage of this? You are understanding it? That this is a molecule which is molecule of a protein which is transmembrane and it bind the internal cytoskeleton with extracellular component and This is a molecule which is molecule of a protein which is internal cytoskeleton with extracellular component.

help the cell for a structural stability. Structural stability. Are you understanding? Are you understanding? Different cells in different tissues need to be structurally attached.

Different cells in different tissues need to be structurally attached. Right? Right? And different cells have different shape. And different cells have different shapes.

Now, this is intracellular proteins. This is intracellular protein which are also called cytoskeleton. which are also called cytoskeleton. As you have bones, As you have bones, you know you are having bone, you know you are having bones, I think you are sure. I think you are sure.

Bones help you in many things including giving you a shape and strength. ...won't help you in many things including giving you a shape and strength. Is that right?

In the same way as you have skeleton, Is that right? cells also have In the same way, Skeleton. cells also have skeletons. These are skeleton proteins, These are skeleton proteins of the cell.

skeletal proteins of the cells. As a group these proteins are called cytoskeleton. So cell membrane inside has cytoskeleton.

There are many many cytoskeleton proteins. And outside there are extracellular, collagen and other proteins. Right, to stabilize the internal cytoskeleton with external extracellular matrix. We use the term for this extracellular matrix. We need some types of proteins which are what?

Trans membrane integral. On one side they can hold the extracellular. Components in other side they should be able to hold the intracellular cytoskeleton.

And these proteins are also example of what type of proteins? Yes. What type of proteins?

Integral proteins. Is that right? So how many functions of integral proteins you have seen?

The integral proteins may be acting as channels, they may be acting as carrier proteins, Yes, ma'am. they may be acting as enzymes, they may be acting as... enzymes and of course they may be acting as what is this?

linker protein. they are link they are producing a link between intracellular protein and extracellular proteins. linker proteins. right?

linker's protein. then integral proteins have one very important function. one more what is that? okay let's suppose this is a protein which is present throughout the membrane and This protein has extracellular component, it has transmembrane component and intracellular component.

Is that right? Let us suppose this protein can bind the insulin. When insulin come, insulin binds over here.

when insulin binds over here right it start giving signals inside so this protein is working as receptor so receptors in the membranes are also integral proteins So today onward remember cell membranes are made of phospholipids and associated proteins. Associated proteins may be integral proteins or peripheral proteins. Integral proteins are transmembrane protein or through and through protein. Integral proteins have many functions. They may be functioning as channels, they may be functioning as carrier proteins, they may be functioning as enzymes, they may be functioning as linker proteins, they may be functioning as receptors.

Is that right? Broadly, broad main categories of, functional categories of integral proteins. And about peripheral proteins, peripheral proteins, as I told you, they are attached to the external.

aspect of the cell membrane or internal aspect of the cell membrane and peripheral proteins are loosely attached or non covalently attached and they are held with the membrane only with the weak very weak electrostatic very unique static forces can be disrupted very easily away from the forces so they can be disrupted very easily away from the membrane the peripheral proteins right and peripheral proteins are basically acting as functionally acting as cytoskeleton sometimes what happen look here inside the cell at this point some proteins are attached like this right or here are some proteins end proteins basically acting as cytoskeleton in the... and they are stabilizing the structure of the cell. Now these protein flamants are attached with the internal aspect of the cell. Right? So they are transmembrane or they are integral or they are peripheral.

proteins? the peripheral proteins. so many of the peripheral proteins which are attached to the inner aspect of the membrane they are component of the cytoskeleton.

they are the component of the cytoskeleton. Even though I told you cytoskeleton protein which is peripheral protein may be associated with linker protein. Even though I told you cytoskeleton protein which is peripheral protein may be associated with linker protein.

It may be associated with linker protein which may link the cytoskeletal peripheral protein with extracellular matrix. It may be associated with linker protein which may link the skeletal peripheral protein with extracellular. Am I clear? Then another important relationship or function of the peripheral protein is, Then relationship or function of the...

listen, some of the peripheral protein are working with the receptor. Let me tell you how. Let's suppose here is a receptor.

and this receptor protein passes 7 times through the membrane. Such receptor which peptide chain passes 7 times, they are called 7-pass receptors. Now 7-pass receptors are integral protein. You are understanding it?

But it may be associated with some other proteins which are attached with it inside. You are understanding? This is a receptor. Receptor is an integral protein.

But when receptor is activated, it gives signal to some protein which is associated inside. This protein which is associated inside, This protein which is associated inside, what is this? this protein may produce, This is an example of peripheral protein so integral proteins may be associated with peripheral protein and this protein may produce let's suppose this protein may give signals further into cell right and activate second let's suppose, this protein may give signal further into the cell, right? And activate second messenger system. Next messenger will activate.

messenger system messenger system actually let me tell you suppose the hormone which come here that is the first messenger Right, when hormone come to a cell that is first messenger. First messenger work with the receptor. Receptor activate some other intracellular protein and intracellular protein produce second messenger.

So in some books they say proteins related with second messenger system are also peripheral proteins. The point which I wanted to tell you that proteins which are associated with the second messenger system they are not integral proteins they are peripheral protein but receptors are integral proteins. That's right.

Any question up to this? Any questions up to this? Okay, we will discuss further detail tomorrow. Okay, we'll discuss.

Transcript for:Understanding Cell Membrane Structure and Function

Transcript for:
Understanding Cell Membrane Structure and Function