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Biochemistry 3(Dr.Kawa) Polysaccharide (Complex Carbohydrates) These are polymerized products of many monosaccharide units. They may be:A- Homoglycans: - homopolysaccharides contains only one type of monosaccharide. Starch A polymer of the monosaccharide glucose, the storage polysaccharide of higher plants consists of two components, amylose and amylopectin forming α-glucosidic chain. The amylose component consists of glucose units linked in a linear fraction by α-1 4 linkages which is a non branching helical chain and comprise of (15-20%) of starch. Amylopectin is a branched chain polysaccharide and comprise of (8085%) composed of 24 - 30 glucose residues united by 1 4 linkage in the chain and by 1 6 linkage at the branch point. Glycogen Glycogen is the analogue of starch, a glucose polymer in plants, and is sometimes referred to as animal starch, having a similar structure to amylopectin but more extensively branched and compact than starch. Glycogen is a polymer of α (1→4) glycosidic bonds linked, with α (1→6)-linked branches. Cellulose polysaccharide consisting of a linear chain of several hundred to over ten thousand β(1→4) linked D-glucose units .Cellulose is derived from D-glucose units, which condense through β(1→4)-glycosidic bonds. This linkage design contrasts with that for α(1→4)-glycosidic bonds present in starch, glycogen, and other carbohydrates. Cellulose, also known as plant fiber, cannot be digested by the human; therefore cellulose passes through the digestive tract without being absorbed 1 into the body. cows and sheep contain certain symbiotic anaerobic bacteria (like Cellulomonas) in the flora of the rumen, and these bacteria produce enzymes called cellulases that help the microorganism to break down cellulose; the breakdown products are then used by the bacteria for increasing the number. Hemicellulose A polysaccharide related to cellulose that comprises ca. 20% of the biomass of most plants. In contrast to cellulose, hemicellulose is derived from several sugars in addition to glucose, especially xylose but also including mannose, galactose, rhamnose, and arabinose. Hemicellulose consists of shorter chains – around 200 sugar units. Furthermore, hemicellulose is branched, whereas cellulose is unbranched. Inulin Inulins are polymers composed mainly of fructose units, and typically have a terminal glucose. The fructose units in inulins are joined by β (2→1) glycosidic bond. In general, plant inulins contain between 20 and several thousand fructose units. Smaller compounds are called fructooligosaccharides, the simplest being 1-kestose, which has 2 fructose units and 1 glucose unit. B- Heteroglycans: heteropolysaccharides containing residues of more than one type of monosaccharide: Agar It is prepared from sea weeds. It contains galactose, glucose and other sugars. It dissolved in water at 100 C° which upon cooling sets into a gel. Agar cannot be digested by bacteria and hence used widely as supporting agent to culture bacterial colonies. Mucopolysaccharides Mucopolysaccharides or glycosamino glycans (GAG) are heteropolysaccharides containing uronic acid and amino sugars. Acetylated amino groups sulfate and carboxyl groups are also generally present. Because of the presence of these charged groups, they attract water molecules and so they produce viscous solutions. 2 Examples: 1.Hyaluronic acid , 2.Heparin, 3.Chondroitin sulfate, 4.Dermatin sulfate and 5.Keratin sulfate. Digest Carbohydrate In simple terms, our digestion system - from the mouth to the small intestine - is designed to break down disaccharides and polysaccharides into monosaccharides, the monosaccharide (glucose) are absorbed into the blood stream and taken to the liver, where it is stored or distributed to cells throughout the body for producing the energy. The liver regulates blood glucose levels to provide sufficient energy for the body. For example, excess glucose (a cause of hyperglycemia) is converted in the liver to glycogen (glycogenosis) in response to the hormone insulin and stored. Likewise, if blood sugar levels fall, (e.g. between meals), the glycogen is re-converted to glucose (glycogenolysis) in response to messages conveyed by the hormone glucagon ,to prevent hypoglycemia. Metabolism of glucose:Polysaccharide disaccharide Monosaccharide glucose which absorbed and converted to:a – Glycogen and stored in liver cells. b- Metabolized to CO2 + H2O to provide energy. c- Keto acids + amino acids + proteins. d- Fats and stored in adipose tissues. There are 4 processes regulate the metabolism of carbohydrates in the body: 1-Glycogenesis: The process that convert glucose to glycogen in liver cells. 2- Glycogenolysis: The process of breakdown of glycogen to glucose and other intermediate products in liver cells. 3-Gluconeogenesis: The process of glucose formation from noncarbohydrates such as amino acids and fatty acids. 4- Glycolysis: The process that convert glucose to Lactate or pyruvate. 3 Hyperglycemia: high level of glucose in the blood. Hypoglycemia: low level of glucose in the blood. Blood sugar The blood sugar level is the amount of glucose (sugar) in the blood . Normally blood glucose levels stay within narrow limits throughout the day: 80 to 120mg/dl. But they are higher after meals and usually lowest in the morning Diabetes mellitus: - Disease characterized by insufficient blood levels of active insulin and this deficiency leads to inability of glucose to enter muscle and liver cells with abnormal metabolism of proteins and fats leading to ketosis and possible diabetic coma. Types of Diabetes mellitus (DM) The classical symptoms of diabetes is polyuria, polydipsia and polyphagia Type 1 diabetes (Insulin dependent diabetes mellitus) (IDDM): is characterized by loss of the insulin-producing beta cells of the islets of Langerhans in the pancreas leading to a deficiency of insulin Type 2 diabetes Insulin independent diabetes mellitus (IIDM): is characterized differently and is due to insulin resistance or reduced insulin sensitivity Gestational diabetes (GDM): It occurs in about 2%–5% of all pregnancies and may improve or disappear after delivery. Estimation of blood glucose Several different types of blood glucose tests are used. 1- Fasting blood sugar (FBS) measures blood glucose after you have not eaten for at least 8 hours.Normal value : 80-100mg/dl 2- 2-hour postprandial blood sugar measures blood glucose exactly 2 hours after you eat a meal. Normal value : <140mg/dl 3- Random blood sugar (RBS) measures blood glucose regardless of when you last ate. Normal value : 100-120mg/dl 4- Oral glucose tolerance test (OGTT) is used to diagnose prediabetes and diabetes. 4