 different classes of carbohydrates, polysaccharides first the contents definition of polysaccharides then the physical chemical properties of polysaccharides some common polysaccharides and the role of polysaccharides in the living organisms friends first we will define polysaccharides if we look at this first thing is that this is the third group of carbohydrates there are three classes of carbohydrates monosaccharide, disaccharide and the final or last class they are the polysaccharides poly means many and saccharide means sugars simply we will define it when many monosaccharides or simple subunit they combine together, they link together they form a large molecule which is called polysaccharides in polysaccharides there are many monosaccharides they form a large molecule which is called monosaccharides if we look at its limits monosaccharides have one subunit there are two subunit in disaccharides there are many polysaccharides in different books what is more appropriate is when there are more than 20 monosaccharides there is a link, we call it polysaccharide 20 and more than 20 monosaccharides have one subunit when they link to each other they form a polysaccharide molecule we call it oligosaccharide physical and chemical properties physical and chemical properties are polysaccharides physical for physical and chemical properties they are not sweet in taste the first properties are taste, if we have a plant it has a bark it has a dry shawl if we keep it in our mouth it will not taste it is called husk husk has grains if you wash it well it will not taste it means polysaccharides are not sweet in taste so it is not sweet solubility in water in solubility in water in solubility in water but if we take it more precisely if we make a better definition they are most of them they are insoluble in water but some of them have little solubility in water there are some polysaccharides which are soluble in water so we call it very little solubility in water all the polysaccharides they are non reducing sugars carbohydrates these are all all the polysaccharides all the polysaccharides are non reducing like starch cellulose, glycogen chitin all the polysaccharides are non reducing general formula of polysaccharides general formula of polysaccharides is C-H2O Y if we look in the summarized way it shows that monosaccharides have a link like in starch there are glucose so the formula of glucose is C6H12O6 so one glucose is thirdly it has a link with each other but when two glucose is linked then one water molecule will be removed so it means the glucose C6H12O6 will be removed from 12 and from O6 oxygen water will be removed so the rest in starch or glycogen the glucose will be basically C6H10O5 so we will implement it in another pattern C6H10O5 we will record C6H10O5 common polysaccharides most common type of polysaccharides are glycogen starch, cellulose and chitin if we look in the diagram first three are glycogen, starch and cellulose these three are the polysaccharides of glucose these are the polymers of glucose i.e. in the three there is a link between the glucose molecules in the glycogen and the starch the molecules of the glucose are called alpha-1-4 whereas the starch in the glycogen and the starch there is alpha-1-4 which is the link between the two glucose molecules whereas in the cellulose there is beta-1-4 in the chitin there is a modified form of glucose which is called n-acetyl-glucosamine this is a glucose molecule with which amino-acetyl group is present this n-acetyl n-4-aminogruple acetyl is present because of this n-acetyl group we will give it the full name n-acetyl-glucosamine this is the modification of the amine group in chitin, n-acetyl-glucosamine is present what is the role of polysaccharide in the living organisms the major role of polysaccharide is that we can divide it in two categories the first one their role as fuel storage and the second one is their role as the structure the structural component, the structural role of it fuel storage what is the fuel it is called as fuel which runs something like when we put a petal in a car what is the fuel of the living organism when we talk about the living organism our fuel is glucose mainly glucose is our fuel if we get glucose it will break down and provide our body with energy all the major polysaccharides in our body are glycogen or we take starch in food so starch and glycogen they store in simple monosaccharides and they provide the body like glycogen glycogen is stored in our body in the liver and muscles whenever the glucose in our blood will reduce it will break down and the glucose will come into the blood so this means that the glycogen is a fuel storage the fuel that the glucose is stored the starch is stored and we use the same stored glucose which is absorbed in our body in our body structural role of polysaccharides the structural role of polysaccharides is that it makes the polysaccharide or it provides only the energy it provides the fuel so in structural polysaccharides there are two famous examples which are chitin and cellulose chitin is the exoskeleton of arthropod there are two groups in which chitin is found one of them is insects and other is crustaceans insects and crustaceans exoskeleton is made up of chitin the structure is like the bones the bones are made up of the same is the case that the insect is made up of chitin and exoskeleton plant is such a big plant and it is in the air there is nothing to provide it its strength is cellulose fibres there are cellulose fibres but the main strength is the cellulose