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Dr. Tarek El Sewedy

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By the end of this lecture, students will learn: 1.Biological function of carbohydrates. 2.Characteristics of carbohydrates Intended Learning Outcomes

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Lecture content Biological function of carbohydrates. Monosacharides Disacharides Polysacharides Physical Properties of Carbohydrates Chemical Properties of carbohydrates

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Biomolecules of life 1. Carbohydrates 2. Proteins. 3. Lipids 4. Nucleic acids

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Carbohydrate Function Sources of Immediate energy (ATP) as produced by glucose catabolism(Glycolysis and Krebs cycle). Source of stored energy (Glycogen stored in liver). Intermediates in the biosynthesis of other basic biomolecules (fats and proteins). Associated with other molecules such as vitamins and antibiotics.

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Cont, Carbohydrate function Structural function: ex. Ribose, deoxyribose and cellulose and starch in plants. Involved in many cell functions such cell-cell recognition and protein folding.

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Digestion of carbohydrates a) -amylase (in saliva) randomly hydrolyzes all the glycosidic bonds of starch. b) Digestion continues in the small intestines with pancreatic amylase. This degrades the starch to maltose. c) Further digestion occurs down the digestive tract in the small intestine. The resulting monosaccharides are absorbed by the small intestine and transported into the blood stream.

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In living organisms, most carbohydrates are found bound to other compounds rather than as simple sugars Glycoproteins (hormones, antibodies) Glycolipids Nucleic acid.

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Monosaccharaides Monosaccharaides are also known as simple sugars They are classified by: 1. Number of carbons. 2. Whether they are aldoses or ketoses. D-glyceraldehyde is the simplest of the aldoses. Glucose is the most widely known

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Glucose Glucose is a monosaccharide with formula C 6 H 12 O 6 It is absorbed directly into the bloodstream during digestion. Bread, rice, pasta are rich in glucose. Glucose is a common medical analyte measured in blood samples.analyte measured in blood samples The hormone insulin, regulates the concentration of glucose in the blood. A high fasting blood sugar level is an indication of diabetic conditionsblood sugar

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Organisms use glucose as a precursor for the synthesis of several important substances. Starch, cellulose, and glycogen ("animal starch").Starchcelluloseglycogen Some of these polymers like starch or glycogen serve as energy stores while others like cellulose have structural roles. In animals, glucose results from the breakdown of glycogen, a process known as Glycogenolysis.glycogen Glucose can also be synthesized in the liver and kidneys from non- carbohydrate intermediates, such as pyruvate and glycerol, by a process known as Gluconeogenesis.liverkidneyspyruvateglycerol Glucose is produced commercially via the enzymatic hydrolysis of starch. Many crops can be used as the source of starch. Maize, rice, wheatenzymatic hydrolysisMaizericewheat

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Glucose is classified as a monosaccharide, an aldose, a hexose, and is a reducing sugar.

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Fructose

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Fructose is found naturally in fruits and vegetables. Fructose is metabolized differently than glucose and other sugars, doesnt stimulate insulin and is characteristically low glycemic. For these reasons, its often used in low-glycemic food applications 15 to 80% sweeter than sucrose, and tastes particularly sweet when cold or in solution

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Disaccharides

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Disaccharides are formed when two monosaccharaides are joined together and a molecule of water is removed. Milk sugar (lactose) is made from glucose and galactoselactoseglucosegalactose sugar cane sugar (sucrose) is made from glucose and fructose.sucroseglucosefructose Maltose is made up of two glucose molecules.Maltose The two monosaccharides are bonded via a glycosidic bondmonosaccharidesglycosidic bond Can be degraded to monosaccharides by hydrolysis producing water.

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Sucrose

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Formed of Glucose and fructose monomers joined together. known as table sugar Commercially obtained from sugar cane or sugar beet Used pharmaceutically to make syrups

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Lactose Lactose is a famous disaccharide, resulting from a galactose joining to glucose. Milk is the most famous source of Lactose. Used in infant formulations, and as a diluent in pharmaceuticals

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Maltose Made up of two glucose molecules. Produced when amylase breaks down starch.amylasestarch Obtained from malt sugar and when glucose is caramelized.

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Polysaccharides

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Starch Starch or Amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds.carbohydrateglucoseglycosidic bonds produced by all green plants as an energy storeplants It is the most common carbohydrate in the human diet like potatoes, wheat, maize (corn), rice. potatoeswheatmaizerice

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Cont, Starch consists of two types of molecules: the linear and helical amylose and the branched amylopectin.helicalamylose amylopectin Glycogen, the glucose store of animals, is a more branched version of amylopectin. Used as an additive for food processing, typically used as thickeners and stabilizers in foods such as puddings, custards, soups, and salad dressings, and to make noodles and pastas.food processing Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.

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Glycogen Glycogen is also known as animal starch. It is stored in muscle and liver tissue Complete hydrolysis yields glucose Glycogen

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Glycogen is the glucose storage polymer in animals, is similar in structure to amylopectin, but glycogen has more branches The highly branched structure permits rapid release of glucose from glycogen stores, i.e. in muscle during exercise. The ability to rapidly mobilize glucose is more essential to animals than to plants

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A. Physical properties of carbohydrates

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D and L forms of sugars Asymmetric carbon atom: It is a carbon atom attached to four different atoms or groups. Any compound has asymmetric carbon posses the following properties: 1-Formation of isomers. 2-Having optical activity Isomers exist in two forms: 1-D-form (when the hydroxyl group lies on right side to the asymmetric carbon atom) 2-L-form (when the hydroxyl group lies on left side to the asymmetric carbon atom). In nature, glucose is found in the D form only. Asymmetric carbon atom

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Cyclic and linear forms Monosaccharides of five or more carbon atoms are present in ring forms. In solutions, cyclic forms are in equilibrium with minute amounts of the linear forms.

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-D-Glucose-D-Glucose Enantiomers (Anomers) and differ only in configuration of OH of the anomeric carbon compared to C #6 The anomeric carbon atom (C#1) can exist as two different isomers called and . Though almost exactly the same, they operate differently in our bodies. For example: Humans have the -amylase enzyme for the digestion of starch, but not the -amylase enzyme for the digestion of cellulose. We can digest starch products such as pasta (-Form) and not paper or wood (- form).

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B. Chemical properties of carbohydrates

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Reduction of monosaccharides producing sugar alcohol: The aldehyde and keto group of monosaccharides can be reduced by H2 + catalyst(non enzymatically) or by enzymes producing the corresponding alcohol. Ester formation: The most common esters of monosaccharidesa are phosphate esters. Ex; Adenosine triphosphate (ATP), glyceraldehydes-3-phosphate. Acid Alcohol Ester

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Reaction with acids: Concentrated acid remove three water molecules from sugar forming furfural from pentose and hydroxyl furfural from hexose. The furfurals further react with phenols (naphthol) present in to produce a purple ring interface. Reaction with bases: Strong alkali as concentrated NaOH on heating leads to condensation of monosaccharides forming yellow and brown resin and caramel formation.

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Deoxygenation of Hydroxyl Groups The hydroxyl groups on Carbon atom#2 of Monosaccharides can be replaced with hydrogen atoms to form deoxy-sugars. Deoxygenation of ribose within a ribonucleotide to form the 2- deoxyribonucleotide is a critical reaction in DNA biosynthesis.

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Biomolecules Interconversion (Acetyl CoA)

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Please Remember

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Students selected for assignment

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ASSIGNMENTS The students are requested to prepare slides about the following topics and delivered before next lecture: 1.Importance of cellulose in plants.() 2.Hypoglycemia.() 3.Hyperglycemia.() 4.Carbohydrates and immunity.() 5.Carbohydrates and cell signaling.() 6.Carbohydrates and as building blocks.() 7.Carbohydrate as fuel()

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Study Questions Mention 3 different functions of carbohydrates Complete: Monosaccharaides can be aldoses or . The starch of human body is called---------. The major carbohydrates in plants is called... Mention 4 functions of carbohydrates.

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Harpers Biochemistry 26 th edition Suggested readings: