Polysaccharides PDF

Carbohydrates Chemistry IV. Polysaccharides  Prof / Ayman El Baz Professor of Medical Biochemistry & Molecular Biology Dr/ Sara El Derbaly Assistant professor of Medical Biochemistry& Molecular Biology Course learning outcomes At the end of the lect...

Carbohydrates Chemistry IV. Polysaccharides  Prof / Ayman El Baz Professor of Medical Biochemistry & Molecular Biology Dr/ Sara El Derbaly Assistant professor of Medical Biochemistry& Molecular Biology Course learning outcomes At the end of the lecture, the students should be able to: Define Polysaccharides. Identify the different types of Polysaccharides Describe the structure of different types of Polysaccharides Recognize the functional significance of the different types of Polysaccharides Correlate the structure of different types of Polysaccharides to their functions. Polysaccharides Definition: Polysaccharides, also called glycans, consist of more than 10 monosaccharide units and/or their derivatives joined together by glycosidic linkage. Polysaccharides Homopolysaccharides (homoglycans): contain only one type of monosaccharide. e.g. starch, glycogen, dextran, dextrin, cellulose& inulin. Heteropolysaccharides (heteroglycans): contain more than one type of monosaccharides. e.g. glycosaminoglycans (GAGs, mucopolysacchrides), & agar. Polysaccharides Polysaccharides are classified according to their function into storage and structural polysaccharides. Storage polysaccharides: Starch, glycogen, dextran and inulin. Structural polysaccharides: cellulose and agar. Polysaccharides Homopolysaccharides  Homopolysaccharides 1. Starch: Complex Carbohydrately Structure: It is a glucosan (α-D glucose units) consists of 2 layers: complex  Inner linear non-branching layer called amylose. Glucose units are linked together by α 1- 4 glycosidic bonds. Iodine reacts with α- amylose to give blue colour.  Outer highly branched layer called amylopectin. The branch points occur about once every thirty linkages forming α 1-6 glycosidic bond. Iodine reacts with amylopectin to give a red- violet colour. starch End product of amaylase enzyme of is multose  ~ Ameeo Y Anylopectin layer Outer 90 % - S Linear unbranched are Both X-glucose 1 - 4 more complex (Branched  Homopolysaccharides Both amylose and amylopectin are rapidly hydrolyzed by salivary and pancreatic amylase to yield maltose and dextrins. Function:  It is the most common storage polysaccharide in plants.  Homopolysaccharides 2. α-Dextrin: & 1-4 / Cat branching points a 1-6 Structure: Starch is partially hydrolyzed by the action of acids or enzymes into dextrins (made of several glucose units) and is hydrolyzed by α-dextrinase. For infant feeding - Function:  Dextrin is used as mucilage. Clawazez)  Homopolysaccharides Dextrose rotations glucose, sucrose 3. Dextran: levs rotation : fructose Structure:  It is formed of α-glucose units (glucosan).  It is highly branched molecule with most links are α 1-6 glycosidic bonds but rarely α 1-4 glycosidic bonds. Function:  It is a storage polysaccharide produced by microorganisms as yeasts and bacteria It is used for intravenous infusion as plasma volume expander for treatment of hypovolemic shock. N.B. Dextrose is D- glucose, a term used in bedside medicine, e.g. dextrose drip. Dextrin is the partially digested product of starch. Dextran is high molecular weight carbohydrate, synthesized by bacteria. Homopolysaccharides 4.Glycogen (animal starch): Structure:  It is formed of α-glucose units (glucosan).  It is highly branched molecule (branches every 10 glucose units; more branched than amylopectin). It yields a red violet color with iodine. Function: The major form of storage polysaccharides in animals and human body. It is found mainly in liver (about 6% of liver mass) and skeletal muscle (about 1% of muscle mass). In fasting: Glycogen is hydrolyzed to glucose for maintenance of blood glucose level.  Homopolysaccharides 5. Inulin: Structure: It is formed of fructose (fructosan). Function:  It hydrolyzed by the enzyme inulinase in plants. It has no dietary importance in human beings as inulinase is absent in human.  It is used in inulin clearance test to determine the rate of glomerular or for kidney wrine) (If invlin will be excreted the the healthy in Reratin Kidney is the creatine If it doesn't get excreted it means it's not healthy) filtration. It can be used as a diet for diabetics..  Homopolysaccharides 6. Cellulose: Structure: It is formed of β-D-glucose units. Function:  It is the most abundant natural polymer found in the world. It is the structural component of the cell walls of nearly all plants.  Cellulose is extremely resistant to hydrolysis whether by acid or by the digestive tract amylases. So, it can stimulate peristaltic movement and prevent constipation.  The bacteria that live in the gut of ruminant animals secrete cellulase enzyme (β- glucosidase) which is effective in the hydrolysis of cellulose.  Heteropolysaccharides Mucopolysaccharides Glycosaminoglycans (GAGs) Proteoglycans · ·  Heteropolysaccharides Glycosaminoglycans (GAGs) are long linear unbranched chains composed of a Do repeating disaccharide units (sugar acid- amino sugar)n. The amino sugar may be either D-glucosamine or D-galactosamine and the amino group is usually acetylated (sometimes sulphated). The acid sugar may be either glucuronic or iduronic. Glycosaminoglycans (GAGs) - galactos glubse Proteoglycans All of the GAGs except hyaluronic acid are found covalently attached to protein, forming proteoglycan monomers.  1-Heparin 2-Heparan sulfate 3-Hyaluronic is not acid aggregated protegiyas to Pure Carbohydrate Sugar acid L-Iduronic acid CHE H - C - H H to - - TH D-Glucuronic D-Glucuronic acid -c H i - L = Leve (left) oi - 3 D right H - = C oh L-idron - H - c A D-glucuronic Amino-sugar Glucosamine Glucosamine Glucosamine (non acetylated) (acetylated) (acetylated) the only one that's not acetylated Sulfate group More Sulfated Less Sulfated Non sulfated the only one that's non-sulfated free Sulfated Site Mast cells lining the Extracellular receptors in cell Synovial fluid of arteries of the lungs, membranes, joints, loose connective liver and skin basement membranes, tissue, vitreous humor of components of cell surfaces eye, skin Main Anticoagulant Component of cell Shock absorbing and function (in the Must cells) surface lubricant in joint cavities. synorial fluid  4- Keratan sulphate 5-Chondrotin sulfate 6- Dermatan sulphate Sugar acid Galactose (not sugar acid) D-Glucuronic acid L-Iduronic acid the only one that does not contain (uronic) Amino-sugar Glucosamine Galactosamine Galactosamine (acetylated) (acetylated) (acetylated) Sulfate group Sulfated Sulfated Sulfated Site Type I is abundant in cornea Mucid connective tissue (Bone, Wide distribution, skin, blood Type II is found in mucid cartilage, tendons, ligaments and vessels and heart valves connective tissue (Bone, joints) cartilage, tendons, ligaments and joints) Main Corneal transparency Elasticity and compressibility of The main GAG in skin. function Support and protection cartilage in weight bearing. Blood coagulation, wound Support and protection repair and resistance to infection.  Heteropolysaccharides Agar A polysaccharide isolated from marine red algae. Composed of agarose and agaropectin. Agarose gel is used in gel chromatography and gel electrophoresis. Nutrient agar is used in preparation of culture media in microbiology. References Vasudevan’s Textbook of Biochemistry For Medical Students, 7th Edition. Chatterjea’s Textbook of Medical Biochemistry, 8th edition. BRS Biochemistry, Molecular Biology, and Genetics, 5th Edition.