 So, we finish the first lecture. So, today we will be starting with the second lecture. So, the first two lectures are about the introduction to physiology of cells and general physiology. So, in the first class, so let me just like this. So, this is how we have divided it, section one introduction to physiology and under that we are dealing with cell and general physiology. And there are two dedicated lectures on this. So, this is the second lecture. So, in the first lecture, we talked about the chemical organization and the way the chemical level of organization has taken place. And in the second lecture today like this, we talked about the chemical level of organization. And in the chemical level of organizations, we talked about the elements, atoms, the compounds followed by some of the inorganic molecules. The major inorganic molecules including water, methane, methane and H 2 S, CO 2 and likewise and so forth. So, today what we will do? We will talk about some of the organic molecules in this lecture. This is the one aspect we will be dealing about the organic molecules. And then we will be dealing about some of the factors like pH and buffers. Then we will be talking about the feedback mechanisms. And we will revisit the structure of the cell at the end. These are the four aspects which we are going to deal about. So, what I will do? I will give you some practical example of feedback mechanisms. What really feedback mechanisms are? So, let us think of a situation. It is a hot weather outside and we go out. Once we go out, we really feel very hot. And when we feel very hot, what we see the next thing is that we have a lot of sweat coming into from our skin and everything. And after some time, we started feeling comfortable. It is ok. You know, we kind of adjust to it. What exactly has happened? You go out. So, here is a situation. Here is a person inside a room. Here, the temperature is fine. And here, there is bright sun. And now, this person goes out. As soon as this person goes out, you see lot of sweating from the body. It is hot, bright sun. So, what exactly happened? At the biological level or at the physiological level, there are two, three things which happened. The very moment, for example, here is a bright sun and this person has gone out. So, the first thing what happens, our body has lot of heat sensors all over its body and which are represented by this green dots. These heat sensors immediately sense that it is hot. And what these heat sensors did? They send a signal to the brain. So, let me put it. This represents the heat sensors. This blue line is neural signal to the brain. So, brain is being told that we are exposed to a very hot weather. And what brain does? At this point, brain does this. It sends back a signal to all these different organs which are exposed to heat, which is brain sending signal to different parts of bodies. The output is the blood vessels. Once the brain signal comes like this, these signals and this is the blood vessel. And here is the signal coming from brain. So, for example, this is the brain from where the signal is coming. These blood vessels dilates or in other words, they start losing bit of a water. They become much more fluidic. And end result is that from the body, the water starts coming out in the form of sweating. And the sweating makes you feel comfortable. In other word, in the form of sweating, there is a heat loss in the form of sweating. So, what exactly happened in terms of engineering? So, a body has a specific temperature to maintain. Say for example, a body maintains, say 37 degree centigrade. It is imagine a room. Inside a room, we decided that room temperature should remain at, say 37 degree. The very moment, the temperature of the room goes up. Say for example, it becomes 40 or say 45 degree centigrade. Automatically, there will be a thermostat switch which will ask the AC to get on. And AC will bring back the temperature to 35 degree centigrade. Vice versa, if from 37, it fulfills down to say 30 degree centigrade. There will be a heater which will get on and which will bring it back to 37 degree centigrade. So, this is how it works. Exactly the same analogy, the body follows. So, body has to maintain an optimal temperature of the body. So, it does so by having something called a negative feedback loop. Negative feedback loop means, so let me put it like this, optimal temperature regulation by negative feedback loop. What exactly happened? So, here is the skin surface. The temperature goes up. Signal is sent to the brain. And a specific area of the brain which is regulating is called hypothalamus. Hypothalamus sends a signal back to this thing and ask the blood vessels to dilate and thereby maintaining the temperature. So, bring it back. Say for example, if this has to maintain a temperature of 37 degree centigrade and this goes up to say 39 degree centigrade, then the hypothalamus tells these muscles or another part of the body to bring it back to 37 degree centigrade. So, what will happen? Because of this signal, this 39 will come back to 37. This kind of feedback loop system is called negative feedback loop. This is one of the control mechanism by which body controls the temperature. There is another feedback loop. This is one such example of feedback loop. There is another feedback loop which is called positive feedback loop. What is positive feedback loop? In the last class or in our first class, I give you an example of blood vessel. Say for example, this is the blood vessel and I told you in this blood vessel, blood is flowing. So, you see these are the blood which is flowing across this vessel. Say for example, there is a small rupture. There is some kind of a rupture. As soon as there is a rupture, what will happen? Blood will start coming out from here. So, as soon as blood will start coming out from here, I told you that there are some specific cells in the blood which are called platelets. These platelets will immediately come at the side and will try to create a kind of adhesive or something which could stop a pipe from where water is coming out. In this situation, the blood is coming out from the blood vessel. So, what is that reaction exactly happening in this situation? What exactly is happening is this whenever there is this kind of say for example, let me take another page to show you what is exactly happening. This is normal situation. There is no reaction stage one. Now, there is a rupture in blood vessel which is this situation when there is this rupture. Because of this rupture, blood starts coming out. The blood starts coming out. This is the stage two. The next reaction what happens is this. These surrounding cells which are present out here, these cells which are present which are lining, they secrete certain chemicals, chemical secretion following the rupture of the vessel. These chemicals recruit the platelets from the blood and these platelets start forming a kind of, you should say a kind of a plug-in in order to close that leakage. So, this process is further enhanced by the platelets because platelets further recruits more platelets to do this job. This kind of system is called positive feedback loop. All across this course will come across several positive and negative feedback loops. These positive and negative feedback loops are the positive feedback loop and negative feedback loop are the lifeline of our survival. They are the one which helps us to maintain something called homeostasis. This word is extremely important. Homeostasis means maintaining the balance or maintaining the normal functioning of the system. That is called homeostasis. So, this homeostasis is dealt at several level. One of the level is the level where we talked about pH and buffering. So, from here from the feedback loop, we will talk about little bit about the pH and buffer systems which regulates our body. Regarding the pH and the buffer systems, so let us put it like this. So, these are the next two topics we are going to talk about. Let us take a practical example. Whenever we all suffer from this problem, whenever we eat something outside or we always say, come on I am feeling very acidic. Whenever we feel acidic, doctor or mother or somebody recommend us, why do not you take an antacid? What exactly does that mean and what does this antacid means? Whenever we talk about acidic, what is acid? What is base? So, these are some of the basic terms which we need to understand in order to understand how these different antacids or any other molecule exactly works in the system. So, let us introduce the concept of pH here, which will help us to understand little bit more about our own body and how it works. Those of you who have forgotten the definition of pH, it is basically negative log of H plus ion concentration in moles per liter. What exactly this means? So, in order to understand this, you have to realize the major component of our body is water. This is water molecule from hydrogen bonding and which you can find in the power plant presentation. There are lot of very nice examples out there and I will keep on citing examples as we will move through. A huge part of our body or the most part of our body is bathed in water. What really water does and from where this concept of pH really arises? So, if you look at this formula of water. So, this could dissociate into H plus and OH minus H minus H minus H minus ionic species. There is a positive ionic species, there is a negative ionic species. Under normal conditions, a very small fraction of water is in ionized state and if I have to give you the value of exactly how much water is in ionized state in a pure 1 liter of water. If I say 1 liter of water, go to the next page so that it will be useful for you guys to understand. So, 1 liter of pure water. So, H 2 O let me redo the reaction H plus OH minus in 1 liter of pure water, your ionic species of this is around 0.000001. Mole of H plus and equal amount of OH 0.000001 moles of OH minus. Now, if you translate this, what does that mean? Let me again write it down 0.000001. There are 1, 2, 3, 4, 5, 6 moles of H plus ions and that means molar concentration wise H plus ions equals to 1 into 10 to the power minus 7 moles per liter and this we consider normal water at this point is called pH is equal to 7. So, this is the basic concept of pH is equal to 7. Now, if I draw the scale like this, now let us draw the pH scale and this is I call this as pH 7. So, pH 7 H plus ion concentration will be equal to 0.000001. Now, in that scale let us see how the other who all lies at different zone. So, this is the left side of the scale and this is extreme right side of the scale. If I come to the extreme left of the scale, this is where lies hydrogen HCl which is around is the pH is almost equal to 0 which is in other word H plus concentration is 10 to the power 0 moles per liter. Same way you have out here you have alcohols. So, that is why whenever you consume alcohol or beer or these kind of things you feel acidic or you know tomato juice or fruit juice. They are all acidic tomato juice or fruit juice. So, whenever you consume this you are increasing the acid of your system and this is pure water and on the basic side of it is the blood your blood body blood is slightly alkaline. This is blood slightly slightly alkaline there is and slightly more alkaline is the egg and then you have the bleach. This is very alkaline and which helps you to clean your clothes. Then you have ammonia and at the further end you have NaOH which is exceptionally basic. So, on this side you have all the acidic component and on this side you have all the basic component. If you look at carefully in this you will see your blood is slightly basic. Pure water is absolutely a dot 7 alcohol pickles and all these things are on the acidic side. Egg which is on a slightly alkaline side and this is what determines where how your body is doing. So, most of the time body tries to maintain the pH somewhere around here except in the stomach where the pH is very low where you have lot of hydrochloric acid. So, this is the overall concept of pH. Now, what is buffer? Buffer is something which helps you to maintain the pH of the body. Now, if I ask you this question what an antacid does? So, basically what an antacid does is some of these antacids which you will see in the market is like you know you use once again. So, say for example, you went for a party and you feel very acidic. You come back and then your parents or somebody ask you know you take some antacid. Some of the antacids in the market are like alka cells and all this kind of thing. These are the brand name of some of the what they are basically. They are basically nothing but sodium bicarbonate what exactly it does. So, say for example, your body has become very acidic and this sodium bicarbonate brings it back and maintains helps to maintain the pH by neutralizing the excess acid which is formed in your system. So, whenever next time onward you take any kind of drug like that you should understand it is basically what you are trying to do is that you are trying to balance the pH of the body and that is how all these small antacids and all this kind of molecule works. So, these are different kind of mechanism. There is another control system which while talking about the negative and positive feedback I did not mention. Let me mention that there it. So, one we have already discussed is negative feedback positive feedback. The other is auto regulation extrinsic regulation what this does this mean. So, extrinsic regulation is say for example, within your body somewhere there is lack of oxygen. So, what exactly happens whenever there is a lack of oxygen or something there is a scarcity of oxygen. The cells which needs oxygen secrete certain chemicals in which dilates the blood vessel and draw more and more oxygen. So, if I have to diagrammatically show it it looks like say for example, this cell in the body this particular cell needs more oxygen. It is deficient in oxygen under this situation what we will do is that. So, for example, there is a blood vessel traveling along in the close proximity of this like this is the red one is the blood vessel. Now, what this cell will do this cell will secrete certain compounds like this and that compound will dilate it will make this vessel more perforated and thereby this cell will draw more oxygen into it. This is a classic example of auto regulation which is taken care by the cell itself. This is one mode of regulation there is another mode of regulation that is called extrinsic regulation. So, extrinsic regulation is the one which I discussed in the first class. I told you which is taken care by the nervous system where the cell or the individual system is depending on nervous system or the endocrine system or the immune system. These are the three systems which takes care of the extrinsic regulation. So, from here we will move on to some of the organic molecules what we discuss which we have in because we talked about the inorganic molecules. We talked about the pH we talked about buffering we talked about negative feedback negative and positive feedback loops. We talked about auto regulation and extrinsic regulation. Now, we will talk about some of the organic molecules which in our next section while we will be entering into the membrane physiology of nerve and muscle that will be very very important. We have to have some basic idea about the organic molecules. The major class for organic molecules which are present in our body let me enumerate them for you guys that will help you to understand. Organic molecules falls under carbohydrate, lipids, proteins, nucleic acid and energy molecules. As we will go through this whole course on innumerable occasions we will be touching upon these. So, at this stage I will give you an overall idea about the structure and where they are present. As we will proceed through the course we will kind of go in depth with these different structures and how they look like and where the changes are taking place and all so on and so forth. So, coming to the first structure which I will be talking about is carbohydrate. So, to start with carbohydrates. So, all of you know whenever you feel tired or something or we take glucose because we say those are that will help you to regain the energy or we take some fruits you know they say they are. So, what exactly we meant by these what are carbohydrates or every time we use it to eat your lunch or dinner you take chapathis you take rice and we say they have lot of carbohydrates. Carbohydrates are simple sugar molecules and how they really look like a general structure of carbohydrate is something like this carbon, carbon, carbon. These are molecules of carbon and hydrogen like this hydrogen, OH group, hydrogen, hydrogen 3, 4, 5 and actually hold on hydrogen, hydrogen here you have the OH group, hydrogen, hydrogen, OH and you have OH here and you have hydrogen here. This is the basic structure of a glucose molecule in the extended ring like structure and the same structure when it kind of you know form in the ring like a it looks like this. Hydrogen, hydroxyl group then you have oxygen here. Hydrogen you have OH here, OH here, OH moiety you have OH here, OH here, you have OH here. So, this is the basic structure of glucose which is the most simplest sugar which is known to us. Now, you have they could be you know monosaccharide, they could be disaccharide I will come to that what does this mean disaccharide, they could be polysaccharide what does this mean. So, monosaccharides are basically glucose and fructose, these are the monosaccharide they are single unit very similar to the one which I drew here this is the monosaccharide. Then you have disaccharide, dye means two where two monosaccharides joints and form a molecule that is called disaccharide. The smallest simple example is sucrose which use a table sugar and lactose which is your milk sugar, sugar present in the milk and you have the maltose. These are dry saccharides and yet there are polysaccharides where there are many such unit which are formed. These are called polysaccharide, polysaccharides are energy molecule like glycogen. So, these molecules are the major source of energy for a body to survive and they could be classified further and another way where you have they could be 3 carbon, they could be 4 carbon, they could be 5 carbon, they could be 6 carbon, they could be 7 carbon based on that they could be triose, they could be tetrose, they could be pentose sugar, they could be hexose sugar, they could be heptose sugar likewise and glucose is an hexose sugar. So, these are the glucose is the hexose. So, this is another way how you can classify them and these molecules form complex with different kind of lipids and they form glycolipids and several other glycoproteins likewise and now from here we will move on to the very simple basic structure of lipids. I will talk about water lipids because this part this is very very essential because as we will be talking about the brain structure which is nothing but bilayer or 2 layers of lipid arranged together which is our next class we will be starting that. So, before we enter in the next class we need to understand what lipids are and how the basic structure of lipid looks like. So, we talked about the carbohydrate in very simplistic manner now we will talk about the lipids. So, lipids are something like this you have a carboxyl end here and there is an hydrophobic tail like this of carbon, carbon tail and this what constitutes something called a fatty acid. This is the basic basic basic structure of fatty acids and within this structure there are several variations which can come up. This chain could be all single bond or this chain could have double bonds based on that they have different kind of nomenclatures. Second way of classification is this chain length that is another way of classifying it. So, if we have to classify them they will look like they could be C 12, 12 carbon, they could be 14, they could be 16, they could be 18, they could be 20 and this is assuming all single bonds on the chain like on this chain all are single bond there are no double bonds. Yet there could be a situation where 16 is to 1 you will see this thing 18 is to 1 or something like you know 18 is to 2 or you will see you know 18 is to 3 or 20 is to 4. So, that means at those different position there are double bonds and based on that. So, I have to classify it is something like this. So, there are double bonds based on that there is another series of classification which called the next page based on the double and single bond of the chain you have saturated and unsaturated fatty acid. I will just give you a small assignment you please look upon what is PUFA and what is the important of it just for your basic knowledge PUFA is a short form it is called polyunsaturated fatty acid. And if you go to a grocery shop you will find different oils mention the PUFA concentration how much PUFA and based on that the housewives prefer which want to buy what is the role of it. This is what I wish you people to look upon on the web or any other book or wherever what really PUFA means what where it is important anyway we will be touching this as we will go further, but I wish you people to look into it. So, this is another set of classification. So, if I go back to the previous slide you see we could have. So, this is how it looks like now single bond double bonds chain length. So, this is the basic fundamental structure of a fatty acid this is the basic structure on that based on the chain length and from there we move on to this could be 12 member 14 member 16 member 18 member 20 member all single bonds. And we have the different double bonds at different places and from there we move on to saturated and unsaturated fatty acids. So, this is the basic structure of the fatty acids, but these fatty acids has further modifications. Those are called another set of lipids which are called triacyl glycerol. We will talk more in our next section about lipid because this is very important for the membrane. So, glycerol. So, you could see this word out here glycerol. So, let us draw the structure of glycerol and now we will talk about what does that triacyl glycerol means. So, the structure of glycerol is something like this there is hydroxyl group is a C H 2 there is a C H here there is a C H there is a C H 2 here there is a OH group here there is another OH group here and this is how it looks like. So, if you look at this structure carefully this is one functional group attached here there is a second functional group attached here there is a third functional group attached here this is the basic structure of a glycerol molecule. Now, on this structure if I represent this structure in a box like this with a OH dangling out OH dangling out OH dangling out and if I modify this OH with say for example, with different fatty acids like this different kind of fatty acids this green ones are the fatty acids fatty acid 1 F A 2 fatty acid 2 F A 3 they could be same same kind of fatty acids they could be different kind of fatty acids based on that. So, basically what will happen when the fatty acid will join this one will get out this one will move out this one will move out and what we will get is a structure like this here is a glycerol here you have 3 fatty acids like this and this structure is called tri because there are 3 acyl glycerol. So, where the fatty acids are becoming part of the main glycerol structure these most of these structures what you see are used for the storage lipids. So, lipids could be classified talked about fatty acids then we talk about tri acyl glycerol where you saw the where you see the modification of F A F A F A and you have the glycerol out here. So, these most of this tri acyl glycerol are called falls under the storage lipids they help in storing energy current. And then there is third one which are part of the called membrane lipids these are even more interesting they have lot more modifications and if I had to draw the second. So, membrane lipids have much more complex structures say for example, this is the glycerol moiety out here and you have fatty acid here you have fatty acid here and you have p o 4 and you have alcohol attached here these are called glycerol phospholipid. These are called membrane lipids and there are many other classes of membrane lipids which will be coming once we will start about the membrane. So, broadly speaking they could be classified as lipids lipids could be classified in terms of their position as storage lipids membrane lipids. This is broadly a classification of the lipids from here we will move on to the third set of molecules which are the proteins. So, we talked about the carbohydrates we talked give you a basic idea of the lipids lipids will be coming back very soon in our third lecture while you will be initiating the membrane physiology of nerve and muscle. And now we will talk about the proteins what proteins are those are the simple language they are the structural block of our body most of the structure starting from your hair your nails your whole body they are nothing but area of proteins. And these are the molecules which are made up of carbon, hydrogen, nitrogen, sulfur, oxygen and with few other metals like you know iron, effe manganese and molybdenum likewise. So, what is the basic unit how we should study? So, basic unit of proteins protein is just like you have seen all of you have seen the necklace. So, necklace is like you know you have a small small beads attached to each other along a thread which forms a necklace or some kind of a mala. So, protein is exactly something like that where you have a small amino acids and these amino acids are attached to each other and form a long sequence something like this. So, for example, this circle represent an amino acid A A amino acid 1, amino acid 2, amino acid 3, amino acid 4, amino acid 5, amino acid 6. These amino acids are attached to each other and form a long chain and that is what makes a protein. And when this chain is a small, this is also called peptide and the chain is very fairly small. And we will talk about different bioactive peptide which plays a critical role in our system. So, how an amino acid looks like? So, an amino acid looks like this C alpha is a C O O carbon oxyl group is a hydrogen here, there is an plus out here and you have a R group. This R group varies R could be starting from hydrogen to several other things and we will talk about it. So, this is the most fundamental structure of an amino acid. This is what an amino acid look like. So, acid because we have the acetic group and it almost look like a zwitter ion because we have a negative and positive charge on both sides. Now, how one amino acid? So, I drew that diagram for you that there is one amino acid here, there is another amino acid here and they are forming a bond with each other. So, this is amino acid, amino acid, amino acid, amino acid 1, amino acid 2. So, what that bond looks like? So, how about we draw the structure C alpha putting the R group here, convenience you have C O O minus you have NH 3 plus. Let me draw another amino acid on the side by side C alpha C O O minus NH 3 plus and H group. So, this bond takes place between these two. These two are involving forming a very unusual kind of bond which is called a which is unusual because of for several reasons. It forms like this again let me draw it that will C alpha C sorry C alpha R group here H here C O O minus NH 3 plus let us draw the other molecule on the other side C alpha NH 3 plus C O O minus R group H. So, what is happening here is the bond. So, this is how it works C O O N H and the output is C alpha N H plus minus water minus water because you have from here H 2 and you get a oxygen from here and that leads to minus water and this bond this whole thing this is called a peptide bond. And there are some unique feature about this bond because here what happens is electron delocalize along the along this and because that is why it is it is a very stable kind of bond it does not really move or it cannot move it is a planar bond. And on this side there are there are it is like it is something like if this is the bond if you look at it if this is the planar bond you have one side you have this carbon and C C alpha and the other side you have another side you have the N C alpha sorry one side you have the C C alpha the other side you have N C alpha. So, and these two are termed as the this bond let me yeah it forms C alpha. So, on two ends one is called the phi the other one is called the psi and this bond is fairly stable it is kind of a planar bond. So, this is it is kind of a planar bond. So, this is what you see out here that amino acid one amino acid one amino acid two and you have a planar bond which is this bond out here. So, this is how they form a long chain and one second yeah. So, they form a long chain. So, talking about the classification of amino acids amino acids can be classified in a in several ways but I will only show one classification of amino acids. So, they could be. So, the classification is based on the R group showed you that R group varies. So, based on that they could be non polar one way they could be polar this R group is equal to R group is equal to polar they could be they could have R group equal to aromatic aromatic residue. This has the significance in terms of estimation of protein they could be positively charged they could be negatively charged. So, among the polar polar R groups what we have is serine therionine, cysteine, aspergine and glutamine and among the non polar you have glycine which is the most simplest amino acids where R is equal to H. Glycine, alanine, proline, valine, leucine, isoleucine and methionine. Among the aromatic amino acids you have which was aromatic group which includes phenylalanine, tyrosine and tryptophan phenylalanine, tyrosine and tryptophan and among the positively charged residues we are having lysine, arginine and histidine and among negatively charged amino acids you have aspartate and glutamate. So, this is the broad classification of amino acids and what I expect that please go through these structures that will be fairly helpful. Now, the last thing what I am going to cover in this topic is the energy rich molecules and the nucleic acids. So, we will not talk in depth about the nucleic acids there are two kinds of nucleic acids. We will come back to them as we will proceed in the course and they are present in a cell inside the cell they are mostly present inside the nucleus of course. So, they may present outside for some reasons. So, these nucleic acids are could be RNA, ribonucleic acid or a DNA. We will not going to in depth at this stage of it, but eventually we will come back to this and then you have the energy rich molecules which are the energy currency, which is energy currency of the cell, which includes ATP molecules adenosine triphosphate. How they look like? Something like that you have adenine base which is attached to a ribo sugar and that is attached to P O 4 phosphate group another phosphate group P O 4 third phosphate group and these bonds these bonds are the most critical ones this one this one these are high energy bonds and body uses these kind of bonds break bond breaking energy for all the purpose. So, this is triphosphate when there is 1, 2 and 3 this is adenosine diphosphate ADP when there is this this third one is removed then it will become AMP when both these are removed you are left with only one that is called AMP adenosine monophosphate adenosine diphosphate adenosine triphosphate ADP. So, with this I will come to the last slide for you people again recapitulating the structure of the cell this is the membrane of the cell we will because next we will be talking about this membrane within the membrane there is another organelle called nucleus which has the nucleic acid which we have not discussed but we will be talking about it and this part this whole part is called cytoplasm which has all the different cell organelles which includes cytoplasm contain mitochondria, endoplasmic reticulum, sarcoplasmic reticulum ribosomes and so many so and so forth and the next class what we will be starting the next section we will be talking about this membrane structure which is the beginning of all the phenomena membranes of different cells and their features. So, with this our first part of introduction to physiology cell and general physiology we are concluding we believe to give you an overall idea this is how the cell looks like and this is how we kind of study the different physiological phenomena. So, basically what happens that these different cells come together and form organize a structure called tissues and these organized tissue like structure eventually form organs these organs eventually form systems and this different systems interact with each other to form an integrative unit by virtue of which and there are different control mechanisms like negative feedback positive feedback auto regulation extrinsic regulations pH control homeostasis buffering and all these things which regulates our body and helps us to you know interact with the system all the time with this brief introduction of these two lectures we will move on to our next topic which will be the third lecture in the series which will be membrane physiology of nerve and muscle. Thank you.