Biomolecules: Carbohydrates (Part-5) [Homopolysaccharides]

Biomolecules: Carbohydrates (Part-5) [Homopolysaccharides]



welcome to my youtube channel learn at ease in this video I will discuss a topic in biochemistry biomolecules carbohydrates part 5 Homo polysaccharides I will start this video by introducing polysaccharides polysaccharides consists of repeat units of monosaccharides or their derivatives which are held together by glycosidic bonds polysaccharides are also called glycans polysaccharides are classified in two different ways classification based on function and classification based on their composition now I will show you classification based on function of polysaccharide wear first type is structural polysaccharides their function is to provide mechanical stability to cells organs and organisms second type is water binding polysaccharides they are strongly hydrated and prevent cells and tissues from drying up and their type is reserve polysaccharides and their function is to serve as carbohydrate stores that release monosaccharides as required osmotic lea less active and they can therefore be stored in large quantities within the cell now I will describe classification based on composition of polysaccharide here polysaccharides are classified into groups that are homo polysaccharides and hetero polysaccharides where homo polysaccharides are polysaccharide made of same monosaccharide repeating unit and hetero polysaccharides are polysaccharide made of more than one type of monosaccharide repeating unit the image on the bottom left represents two types of homo polysaccharides and they are branched homo polysaccharides and unbranched homo polysaccharides in the image all the repeating units are represented using same color which suggests that all the repeating units are the same the other image appearing on the bottom-right represents two types of hetero polysaccharides and they are branched hetero polysaccharides and unbranched hetero polysaccharides in the image the repeating units are represented using different color which suggests that the polysaccharides is composed of more than one type of monosaccharide units in this video I will explain some examples of homo polysaccharides now I will explain some examples of homo polysaccharides where the first homo polysaccharide is starch starch is a homo polymer of glucose forming an alpha glucose it Akane called a glucose Anor glucan it is the most abundant dietary carbohydrate in cereals potatoes legumes and other vegetables the two main constituents are one amylose which constitutes 15 to 20 percent of starch has a none branching helical structure possessing alpha one four linkages and two amylopectin which constitutes 80 to 85% of starch consists of branched chains composed of 24 to 30 glucose residues united by alpha one four linkages in the chains and by alpha one six linkages at the branch points dextrans are intermediates in the hydrolysis of starch hydrolysis by alpha 1-4 amylase is yields maltose and glucose the image shows the unbranched polymer of amylose where the glucose residues are linked to each other by alpha one four linkages is shown the following image represents the structure of amylopectin where alpha one four linkages and alpha one six linkages is shown the image shows that the branching in amylopectin occurs by the presence of alpha one six linkages the image on the bottom right shows another representation of alpha one six linkages in amylopectin now I will represent another example of homo polysaccharide glycogen glycogen is the main storage polysaccharide of animal cells like amylopectin glycogen is a polymer of alpha 1-4 linked subunits of glucose with alpha one six linked branches but glycogen is more extensively branched on average branching occurs after every eight to twelve residues and more compact than starch and it is more branch than starch glycogen is stored in the liver cells known as hepatocytes glycogen molecule has as many non-reducing ends as it has branches but only one reducing end third example of Homo polysaccharide that I will represent is cellulose cellulose is the chief constituent of the framework of plants it is insoluble and consists of beta-d-glucose ireneaus units linked by beta 1-4 bonds to form long polymer consisting of 10,000 to 15,000 d glucose units straight chains strengthened by cross-linked hydrogen bonds cellulose cannot be digested by mammals because of the absence of an enzyme that hydrolyzes the beta linkage the image shows the structure of cellulose which possess beta 1-4 bonds and alternate arrangement of glucose residues dextran is the fourth example of homo polysaccharide that I will present dextrans are bacterial and yeast polysaccharides made up of alpha 1 6 linked poly D glucose all have alpha 1 3 branches and some also have alpha 1 2 or alpha 1-4 branches dental plaque formed by bacteria growing on the surface of teeth is rich in dextrins now I will show fifth type of homo polysaccharide is chitin chitin is a structural polysaccharide in the exoskeleton of crustaceans and insects and also in mushrooms it consists of n acetyl D glucosamine units joined by beta 1-4 glycosidic linkages the only chemical difference from cellulose is the replacement of the hydroxyl group at c2 with an ascent elated amino group the image represents the structure of chitin similar to cellulose chitin possess beta 1-4 bonds and alternate arrangement of n-acetyl glucosamine residues carefully see the image to understand the structure stay tuned for my next video on hetero polysaccharides which are the polysaccharides made up of more than one type of monosaccharides repeating unit in my upcoming video I will explain glycosaminoglycans and its subtypes glyco conjugates and it's subtypes and I will briefly introduce you with lectins references used to prepare this video are given here if you are new to my channel please subscribe below thank you for watching my video this video is prepared by dr. Dre PI and goes

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