 So, welcome back to the lectures in animal physiology. In the first two lecture, we talked about the introduction to physiology, cell and general physiology. So, that was our first section, we covered two lectures. Now, we are into the third lecture as well as in the section 2. So, this will be the first lecture of section 2 and our section 2 is about membrane physiology and nerves and muscle. So, this is section 2 membrane, which is the one of the most key feature of any entity and we will be taking two examples of nerve cells and the muscle cells and their membrane phenomena. So, in this section, we will be covering two lectures, sorry, we will be covering three lectures in this section. So, what we will do now, we will start with the first topic, which is membrane structure and dynamics. So, under membrane structure and dynamics, we will be covering the introduction to the, introduction to the membrane that will be our first topic, which I will be covering in this lecture. The second thing is the common characteristics or common features among membranes of different species. Say for example, we have plants, we have animals, we have many things, bacteria, algae, they all have membranes. So, what are the common features of membrane from diverse life systems? This is the second topic, which we are, third topic we were going to cover it will be, so this was our first, so again. So, third thing what we are going to cover will be the major classes of the lipids. As you remember in my last lecture, I told you the membranes are form of lipids. So, we will be talking about the complete classification of the lipids and then role of lipids at air, water interface and then we will be touching upon lipid bilayer and its significance. So, with this, let us move on to the first topic, which is the basic introduction about the lipids. So, there are wide range of lipids all over the system. So, the, let us start with the basic structure of the membrane. So, there are wide range of membranes all over the systems and we will be talking about the basic characteristics of the membrane. So, for example, whenever I, if you remember in one of my first lecture, I drew a cell like this and I told you this is the membrane and this is the nucleus. This is the outer membrane and what basically it is doing and it has another membrane, which is called the inner membrane and you have the nucleus in the inside the cell. So, what you will be dealing is, we will be dealing with the structure of this. So, this particular, these kind of membranes or any membrane as a matter of fact has some common features. One of the first common feature is that they are selectively permeable. This is the common, very, very common feature, selectively permeable. In other words, what does that mean? That means that any entry or exit of molecules across this membrane is completely regulated. It is a regulated event. It is not that anything can go in and anything can come out of it. It has to be very, very well regulated. So, that property is called selective permeability and in some books, you will find this is also called semi permeable membrane. It is not permeable to everything. It is permeable to only selective entities. So, all the membranes are like that because why it is very essential for us to understand why the membranes are semi permeable? So, we all believe the life has evolved from ocean and as you know, those of you have been to sea, ocean or bays, you must know that ocean water is very salty and it is exceptionally challenging for biological phenomena to happen in such a salt water. So, somewhere other life has to form. The first membrane has to form where we got rid of the salts and we formed an enclosed structure which does not have that much high salt concentration. So, that is why the first membrane which was formed and evolved may have developed a mechanisms by which it could regulate the solute concentration inside it especially the salt concentration like sodium, potassium, calcium and all these things. And we will be talking about this and how the concentration of this different ions like sodium, potassium, calcium, magnesium varies from inside and outside the cell and what regulates all these things and this feature falls under the selective permeability of the cell. The second feature is that what actually dictates the selective permeability of the cell? Selective permeability of the cell are governed by, so if this is the membrane you see, this is say for example, this is the inner round term membrane. There are wide range of channels out here, there are channels which are like gate you know, there are pumps which regulates. So, pumps channels and you have small pores, these are the ones, these features, these three features and many other features decides the semi permeability of the cell. So, this is another common feature among the cellular structure. The third aspect is in this stuff say for example, think of it whenever we feel heat or cold, our skin responds to it. In other words this is the skin, this is responding to some kind of hot or cold. So, it means these are consist of all different cells. So, these cells have different sensors on their body, on their top. So, in other words if I had to draw it, it will be like this, on top of this you have these kind of, so say you have sensors. These could sense several things, these could sense light, these could sense sound, vibration and we will come to that, this can sense temperature, this can sense once again, this can sense water and several other things and these features helps a cell to respond to the external stimuli, these are all outside external stimuli. So, this is another feature of the cell, there is another feature which is most of these cells say for example, if I draw the cell now like this, these cells changes their permeability and has the ability to generate signals, which could be electrical in nature, signal generation ability, signal generation feature. This is another common feature of the different cells, different membranes present in the cells, which includes the nerve cell, we will be talking depth eventually on this and the muscle cell, which includes both kind of muscle, the cardiac or the one which is forming your heart and the skeletal, which is forming most part of your body and apart from it, there are another set of muscles, which are called smooth muscles, which lines your intestinal or gastrointestinal tract. So, these have the potential or these cells have the feature of generating electrical signal as well as chemical signals. So, this is another feature of the, of these kind of membranes, which are developed and there is one more feature, which is very, very fundamental to the very core of our existence is the bio energetic features. That means, there are membranes, which is the ability to trap sunlight and convert it into electricity. What we see in the plant kingdom, which all of you must have heard something, a word called photosynthesis. So, what exactly happen in that is this, there are some specific organelles, which are present in the cells of the plants, which are called chloroplast. This chloroplast has the ability to absorb light and in the membrane of the chloroplast and this light energy is converted into electrical signal, electrical energy and by virtue of which the energy rich molecule or energy molecules are synthesized. And in our, this is of course, this is an example of the plant system, same happens in the animal king animal system, which we called as oxidative phosphorylation, by which oxidative phosphorylation, this takes place in the mitochondria of the cell. And we must be remembering, I was talking about the mitochondria in the last class and of course, we will go in depth into it. So, this is also a membrane phenomena. So, if I had to summarize, what all the common features the membranes have, the introduction, it is semi permeable in nature. The membranes have channels, pores and pumps in their structures, they respond to different kind of a stimuli, which includes light, sound, water, volatiles like a smell, you know, we smell through our nose, we could figure out whether this smell is bad or good or it is a perfume or is it some other stinking a smell. Then most of the membrane, there are series of membranes, which is the ability to generate chemical or electrical signal, which include nerves and muscles. And yet, there are some specialized membranes like membranes of the chloroplast in the plant kingdom and the algal kingdom, which is the ability to convert light energy into electrical energy, as well as there are membranes in the mitochondria of the cells, which has the ability to do oxidative phosphorylation to generate energy. And that is why in mitochondria is called the energy unit of a cell or the power strength of the cell. With this brief introduction, now we will go on to the part two of this membrane structure and dynamics, that is all these membranes are found in several systems. It could be plant, it could be animals, it could be algae, it could be anything and everything. So, what are the common features? So, now we will be talking about the second thing, which are the common features among common features of membranes among the diverse life forms, which are present on the floor of earth. So, talking about the common features now, now we are moving into slightly more details. Common features of membranes from diverse species of life form. So, this is the aspect, which we are going to deal with now after once we have done with it. So, the first and foremost feature, let me highlight here. Membranes are made up of, most of the membranes are made up of lipids. The major component is lipids along with proteins, which we have talked yesterday. And I promise that I will be coming back to the classification of the lipids of the structural or the membrane lipids in this lecture, and which I will do very soon. So, most of them are made up of lipids, proteins as well as on the top of these proteins and the lipids, there are carbohydrate molecules which are attached to them. So, in other words, if I put the first common feature about them is that membranes are made up of lipids. One of the key component, proteins another major component and third component is your carbohydrates. And these lipids and proteins are present at a specific ratio in all the membranes. They are 1 is to 4, 2 is to 1. This is the ratio in which these are present and on all these lipids, the carbohydrate moieties are attached or in the proteins. So, when they are attached to the lipids, they are called glycolipids. And when they are attached to the proteins, they are called protein carbohydrate things which are glycoproteins. So, it could be attached to the lipids, glycolipids. If carbohydrates are attached to proteins, it is called glycoproteins. So, this is the first feature of that the membranes are made up of lipids, proteins, the major component and the component of carbohydrates which are attached or covalently linked to the lipids as well as to the protein molecules. This is the first feature. Now, from here we will move to the second feature. Second feature is while I was drawing the membrane, it is something like this. So, what is the thickness of the membrane whenever we talk about this? So, most of the membrane varies from 6 nanometer to 10 nanometer depending on the life form 6 to 10. So, in other word it varies from 60 angstrom to 100 angstrom. So, this is the dimension of the membrane. Most of the membranes are of that dimension. Now, talking about the membrane structure, you have a specific I told you that they are a specific proteins all over the place. They are embedded like this and the rest is all lipids. So, these red ones are the proteins which are embedded out there likewise and the green shading what I am doing now are the lipids like this and we will come to the orientation and all those of the lipids something like this. Now, these specific proteins which are present in the red what you see out here in this picture, they have very very specific functions. They could be channel, they could be pores, they could be pumps, but they have specific functions, specific role to play and these are the proteins. Then, you have these lipids which are present there. We will come to the dimension of the lipids. Before that, let me tell you another very interesting feature of the membrane. Most of the membranes are electrically polarized. What does that mean? This is a very interesting feature. That means if I put an let me show you in the next slide. If this is the membrane like this and if this is a membrane and I have one electrode which I am putting inside the cell, another electrode outside the cell and if I measure the voltage across it, I will find that there will be a voltage difference. So, in other word, electrically both sides are standing at different voltage and this feature is called membrane is polarized. We will come back to this while we will be talking about the nerve and muscle. Membrane is polarized and with respect to outside, the inside most of the time stays at minus 80 millivolt with respect to outside, with respect to outside. In other word, outside is more positive as compared to inside. We will come in depth on into this as we will be talking about the nerves and muscle. For this, for the timing just accept this with respect to inside, outside is more positive. The next feature is I talked to you about, now I will come on to the features. How the, so this is the membrane, how the lipid molecules are oriented into it. So, the way lipid molecules are oriented in order to draw this, I have to recollect or take you back to my last lecture, where I showed you how the lipid molecules look like. You guys remember that when I showed you that this is like C O O and O minus and you have the hydrophobic tail. In other word, this part, the one which I am now drawing in red, this part correspond to this part. This is the part which I drew in red is water loving part. This is the one which loves water and the one now I am shading in green, sorry blue, sorry blue. This is the one. This is the water hitting part or in other word, this part is the hydrophobic part and the water loving part is the hydrophilic part. The way the membrane is arranged and we will come to that how it is arranged. Just I will draw it for your understanding sake is like this. The circle what I am drawing you see pointing on both sides. So, basically your polar head groups, these are called polar head groups now which I am shading and here is a polar head group, polar head group, polar head group, polar head group, polar head group. These polar head groups what you see here, here, here, here, here, here. These polar head groups kind of arrange in a very specific fashion, the way I am drawing it you see. They are arranged like this in a membrane, something like this and we will come to that why they are arranged like that and what are the reasons why they form that particular geometry. We will come back to this, but what I wanted to highlight here is this. Then this membrane, these polar head groups, these lipids can move like this along the membrane likewise. These ones which are facing inside, if this is inside and this is outside, the one which are facing outside they could move like this whereas, the one which is facing inside could move like this. What cannot happen is that the one which is facing inside cannot flip to outside. There cannot be a flip-flop movement. Let me draw it for you that will make sense. So, for example, this is part of the membrane I am drawing. The red ones are showing or facing outside and say for example, the green ones are facing inside and these are the hydrophobic tail what they are having likewise. And as we mentioned, so this is say outside the cell, this part is outside the cell, outside and this is inside the cell. This is just part of the membrane I have drawn. So, now let me give them some numbers. So, this polar head group I number C 1, C 2, C 3, C 4 and I name this as H 1, H 2, H 3, H 4. So, H 1 can now be careful. So, H 2, H 3, H 1 can move where H 5 is or H 4 is. Same way, H 4 can move here. There will be lateral movement like this. They could move like this, but same way C 1 can move here, C 4 can come here, C 2 can go there likewise. They could move like this, but what they cannot do is that it is very rare situation when you see a red facing inside and a green facing outside. This is really tough and this kind of movement of flip-flop, this is called a flip-flop. Flip-flop is very, very rare phenomena. It does not really happen. It is really, really tough, but there will be a lateral movement and because of this lateral movement sometime a membrane is called also called a two dimensional solution of oriented proteins and lipids, two dimensional solution of oriented lipids and proteins, because they could only move in the two in the two dimensionally laterally. So, this is a very, very interesting feature about the membranes. So, these are some of the common features of the membranes and there is one more, which is very, very interesting for you guys to really realize here whenever again let me draw the membrane to tell you. So, let me draw it like this showing all the head groups in red outside and the head groups and showing the hydrophobic tail like this. So, another interesting feature about this kind of thing is that this is asymmetric in nature. What does that mean? This means the chemical feature of this, if there is some kind of say for example, carbohydrate modification or some kind of you know other molecule modification. The properties of this surface, the inside surface is entirely different from the properties of the outside surface, because of the modification on their chemical moieties and this feature is called asymmetric nature of the membrane. This is very, very critical. The properties here are different from the properties outside and there is one more feature, which is very critical in this structure is if I again redraw the membrane and if these are the polar head groups outside and these are the polar head groups of the lipids inside likewise. And here you have the, just for the simplicity sake, I am not drawing the full thing. So, what is very important here is that these lipids and the proteins, which are attached say for example, there are different kind of proteins say. Let me use another color, which will make it more easy like the proteins, which are attached likewise. This all these arrangements are basically a non-covalent interaction between lipids and proteins. This is very, very important non-covalent interaction between lipids and proteins. So, if I had to summarize what all the features we talked about. We talked about the asymmetric nature of the membrane. We talked about the fluid structure. You could see the lateral shift among the lipid moieties, but you will rarely or most unlikely you will see a flip-flop movement. We talked about the electrically polarized nature of the membrane. We talked about the different proteins, which are present. They offer different kind of features, which you could see here. They offer different kind of features. And apart from it, we talked about the ratio of the lipids and proteins is 1 is to 4 to 4 is to 1. And we talked about the thickness of the membrane, which is approximately 6 nanometer to 10 nanometer or another 60 angstrom to 100 angstrom in nature. And all these lipids are amphipathic in nature. In other word, most of these lipids have something like this. They have a polar head group, which is water loving and they have a hydrophobic tail. Let me choose another color that will make more sense. So, if this is the polar head group sitting there and these are the these are the hydrophobic tail, which is there. So, this is the one. These are the ones where you see the C carboxyl group sitting there and you have the hydrophobic tail out there. And this is called the polar head group and this is the hydrophobic tail. So, these are the common features of different membranes, what we talked about. From here, I will move on to the part 3 of the membrane structure and dynamics that constitute the classification of the membrane lipids. In the last class, we talked about the lipids. We introduced the lipids and I told you there are two kinds of lipids, the storage lipids and the membrane lipids. And I promise that membrane lipids needs a very separate treatment because it is a very broad class of lipids. And what I will do now, we will classify them so that people understand exactly where which kind of lipids are being used. So, we will go for a generic classification. From there, we will go for the specific lipids, which are present in the membrane. So, our next topic, we are moving into classification of lipids. We started the classification yesterday. Classification in the last class, sorry, classification of lipids. So, the broad classification of lipids are storage lipids and membrane lipids. These are the most broadest of the broadest classification. Among the storage lipids, in the last class, we talked about glycerol moiety. Those of you remember it, glycerol. And on glycerol, I told you there are fatty acids, which are attached to it, fatty acid, fatty acid, fatty acid. So, F A stands for fatty acids. So, these are called glycerol moiety these are the basic storage lipids, what we have already discussed. So, today we will start with the membrane lipids and all the classification of the membrane lipids. So, let us get into the classification of the membrane lipids. So, membrane lipids could be broadly classified into three groups. One is called phospholipids. The very moment you hear phospho, it means there is a phosphorous phosphate group out there. One second, let me get the spellings right. Phospholipids, then you have glycolipids and then you have some very special kind of lipids, which are only found in archaebacteria. We are not going to talk about this just for your knowledge. I am just putting it archaebacteria. They are not found in very many organisms and these are called ether lipids ETHM. They have ether groups in them. So, this is the group, which we are not going to really talk in this course, because this is not really our major interest. Our interest lies with these two groups, glycolipids and phospholipids, because these are the lipids, which constitute a big or the major chunk of the membrane. So, the phospholipids could be further classified into two groups. They are called glycerophospholipids. This is one classification. The other one is sphingolipids. We will come to that. What does that mean? Sphingolipids. Similarly, the glycolipids are classified into two groups. One is called same with the same name as sphingolipids and the other one is called galactolipids or sulfolipids. Galactolipids or sulfolipids. This is another class. Now, what we will do? We will talk about. Now, we will take up first the phospholipids. Within phospholipids, we will talk about the two phospholipids, which includes sphingolipids and glycerophospholipids. Sphingolipids and glycerophospholipids. Whenever you go through the books, you will find these structures to be very complex, but they are actually not very complex. They are very straight forward structure. Glycerophospholipids is very similar to the original lipids. Let us talk about glycerophospholipids and how they look like. So, glycerophospholipids looks like this. You have the glycerol moiety out here, which I was drawing yesterday. You can go back to my previous lecture and you will see the structure of it. Glycerol, which you have fatty acid attached, fatty acid. You have the second fatty acid, which is attached. Then, you have some modification. You have this bond and you have p o 4 or a phosphate group sitting there and an attached to the phosphate group is an alcohol or a OH group sitting there. These are called glycerophospholipids and this phospho is coming from glycerophospho. So, here is that phospho group. Glycerophospholipids. Next we will go talk about the sphingolipids in that class. Under the class of phospholipids, we talked about glycerophospholipids, GPL. Now, we will talk about sphingolipids. What are sphingolipids? Sphingolipids have a very similar structure. I will draw the structure of sphingosynmoiety that will help you to understand. So, this is the sphingosynmoiety, which I have drawn now. I will draw the chemical exactly the chemical nature of it, how that looks like. On that, you have a fatty acid attached here and under the underneath it, you have this phosphate group sitting there and it is attached to a choline. What so? There are two new things, which I have introduced now, which I have to highlight. One is what is this group? This group is called sphingosyn. Sphingosyn group and I introduce another thing, which is called a choline group. Phosphate, of course, I have in care. So, what is this choline group and what is this sphingosyn group, which constitute this? So, what I will do now? I will draw the sphingosyn group and the choline group for you people. Now, let me draw what is the sphingosyn group? Sphingosyn group. So, this is like ch, ch double bonded with ch, ch2. You have 12 molecules of it and then you have this thing and on this side you have the OH, alcohol group ch, NH, C double bonded with O and you have the whole fatty acid attached. So, this is the part of the fatty acids. Fine and then you have underneath it you come back. This is the CH2O and then you have this X, which is which could be anything and everything. We will come to that. So, sphingosyn is basically, this is the basic structure of sphingosyn. So, if you look at it, this is how it looks like. This and this and if we go back into the structure, it is very similar structure if you look at it from here to here and look at it. So, this is the sphingosyn moiety along with the fatty acid come back. Now, what is this X and where I was telling you that this X matters. So, this X was attached to the phosphorous and there is a choline group. So, now, I will draw the choline group, how the choline group looks like. So, that choline group X is equal to will be ch2, ch2 plus ch3 plus ch2 plus ch3 plus ch3 plus ch3. So, this is the choline group. Now, if you go back to the structure of sphingolipids under phospholipids, you have sphingolipids and within the sphingolipids you have, this is the sphingosyn moiety. Here is the sphingosyn moiety. Here you have the fatty acid moiety and then here you have the p4 moiety and attached to the choline moiety. So, this is the structure of sphingolipids, the generic structure of sphingolipids and there are many other modification into it. From here, we will move on to the second class under the broad heading, there is a second class called glycolipids. So, I told you there are two classes. One is the phospholipids and another is the glycolipids. Within the glycolipids you have again two classifications we talk about. One is the sphingolipids. The very moment you hear this term is sphingolipids. So, you can pretty much blindly accept that there will be a sphingo moiety and then you have this galactolipids or sulfolipids and the broad heading of it. So, now what we will do, we will draw the sphingolipids under the glycolipids. So, that you do not lose track, I am repeatedly writing it sphingolipids and then on top of that you have glycolipids. Within that is the sphingolipids. So, what you can do, you can draw a sphingosyn moiety likewise and you can attach the fatty acid group. This is the sphingosyn moiety, this is the sphingosyn moiety which I am shedding in green now, sphingosyn and on top of this you have the x here and this x is replaced by a carbohydrate. It could be a monosaccharide, it could be a oligosaccharide, oligosaccharide or disaccharide. This carbohydrate could be a mono, you remember in the previous class we talked about monosaccharide, disaccharide or oligosaccharide likewise. It could be anything that x is equal to and these are called sphingolipids under the category of glycolipids and apart from it, there is another class within that within the glycolipids. Glycolipids is written for G L and within that we talked about the sphingolipids. Now, we will be talking about another one which is called galacto or sulfolipids. How these looks like, galacto or sulfolipids? So, this is how it looks like. So, again you have a sphingosyn moiety, sorry you do not have a sphingosyn moiety here, you have glycerol moiety, you have a glycerol out here, you have a fatty acid attached here, you have another fatty acid attached here, F A, F A, you have the two fatty acids attached there, then there is a modification here. You have disaccharide or a oligosaccharide attached here, disaccharide or let me put it as carbohydrate here and to that you have a deorite, you have a sulfate moiety SO 4 attached there. So, these falls under, so because of this, this sulfo here is the sulfo group, here is the galacto group or mostly the disaccharide because the galactose which is a disaccharide. So, you have the disaccharide here. So, that is why it got the name galactosulfolipids, in the words something like. So, you saw the galactosulfolipids. So, this is the broad classification of the lipids which is exceptionally essential for you people to understand. Whenever we talk about membranes, you have to have a fairly good idea about the different lipids which actually constitute the membrane and the membrane constitute of the two broad classes of lipids, what we talked about the phospholipids and the glycolipids. These are the two major classes and they have some very, very interesting features which play a key role in the whole evolutionary process and what we are today. So, now what we will do, we will talk about couple of very simple experiments which had been done to figure out what exactly is the structure of these membranes in terms of self assembling and why I was drawing. If you remember, I was repeatedly drawing something like this, whenever I have drawn the membrane, I drew it like this and I told you that I will answer this question once we finish the lipid classification something like this. So, these are the polar head groups which are I showed, these are the polar head groups of the lipids which are facing inside the cell and I am showing inside and outside by this is I inside the cell and this is outside, outside the cell and you have this fatty acid chains or hydrophobic tails which are facing inside in order to minimize the energy. So, why I drew it like this? So, in order to understand this, I have to take you to a very, very old experiment I think remember correctly it was done by Benjamin Franklin what I figured out. So, all of you must have seen this to explain this whenever you go to a bathroom or something and the oil spills out you see a oil forms a layer on top of the water or say for example, you have a beaker of water and you put some drop of oil, how much over you try to mix it it would not, it will form a layer on top of it or say for example, if there is oil spill in any kind of water or in a water body, you will see the oil is floating on top of it because it is a very low density. So, it floats on top of it, but exactly how the interface looks like because now I have mentioned that most of these lipids and everything they have a hydrophilic group and a hydrophobic group. So, let me redraw just to answer this question. So, whenever you talk about this is the polar head group and this is the or this is the hydrophobic tail and when you draw it chemically it looks like this C double on it O minus and you have this polar tail curve. So, this part has the ability to interact with water that is why it is called the polar head group polar head group and this one is the hydrophobic tail. So, most of the lipids are like this. So, what exactly happens when oil falls on the surface of water? So, there are two it is the interfacial phenomena there are two situations one part of the oil is facing the air and part of the oil is facing the water. So, at the air water interface. So, for example, let me draw it this is water. So, this is water and this is air and you have a drop of oil which is falling the way it works is that drop of oil which is falling all the polar head group which could interact with water they orient themselves like this draw like this. So, that you know they orient themselves like this and. So, these moieties can interact with water and their hydrophobic tail faces towards water this is how it works and not only that if they could form some of these could even form something called micelle in water micelle is a structure like this. So, say for example, there is lot of lipids like that and the hydrophobic tail something like this this is called a micelle and this is inside water. So, this is the micelle formation then why I was while I was drawing the cell why I drew it like this if you remember I was drawing it like this and I showed you like here I draw a by I draw a double layer why I drew it like this in other word drawing I made was like this why this was not similar to a micelle why it is like this the reason lies as I told you the membranes are formed from two major lipids which are phospholipids and glycolipids. So, these phospholipids and by glycolipids whenever you add them in water say I designate as p l and g l in water they have a tendency to form bilayer in other word the one which I was drawing let me go to the next page since they form a structure like this these are again the polar head groups this is their innate tendency and this tendency comes because of certain energetic reason where I will I will tell I will give an example of another lipids which does not have a tendency to form like that and which exactly form a micelle. So, you have to understand the difference between micelle and a bilayer structure. So, these are the hydrophobic tail so this is a tendency of this phospholipids and glycolipids to form like that because these phospholipids and glycolipids these hydrophobic chains are very very very bulky and they prefer they prefer to form a bilayer structure instead of forming a single layer micellar structure like this which I was showing you just before couple of minutes back I was showing you the micellar like structure this structure is only shown by some of the lipids like sodium palmitate and these kind of lipid they have a single chain. So, the reason is I told you that you know most of them have this kind of structure they have two tails or in other word the moiety has a structure like this is glycerol glycerol and they have this these bulky chains these are the fatty acids these ones prefer these kind of structures prefer to have bilayer kind of a structure. Whereas, if you have a fatty acids which is something like a single fatty acid chain like this these one prefer to form micelle and one such example which is used in soap in the soap is sodium palmitate sodium palmitate invariably will form micelle as compared to phospholipids and the glycolipids. So, this is what I expect for you people to understand like these are some of the very very basics of the lipid structures which are very very essential in understanding the how the membrane is formed and how it interact to in order to summarize. So, I will say there are five different features which is very essential one the feature one which is very essential is this bilayer formation which is directly linked to the energetic feature of phospho and phospholipid. Plus glycolipids this is extremely essential for you people to understand there is a major hydrophobic interaction between the limits between the lipids in order to form the membrane hydrophobic interaction between lipids is the driving force is the driving force is in membrane formation this is extremely essential. Next thing is that there is a van der Waal interaction between hydrophobic tails this is also very critical feature then you have electrostatic and hydrogen bonding attraction between polar head groups and water and water this is another critical feature and last but not least if I have to summarize it I will put it like this lipid bilayer are non covalent non covalent co-operative. Structure this much I expect all of you to understand this is what is this basic understanding is essential in order to understand the membrane physiology and the membrane processes which are key to our survival growth and evolution. Thank you.