L8 Chemistry of Carbohydrates PDF

L8 Chemistry of Carbohydrates Biochemistry Dr. Salah Omar December 11, 2024 www.gmu.ac.ae College of Health At the end of the lecture, you should be able to Define a carbohydrate. Explai...

L8 Chemistry of Carbohydrates Biochemistry Dr. Salah Omar December 11, 2024 www.gmu.ac.ae College of Health At the end of the lecture, you should be able to Define a carbohydrate. Explain the basis for the nomenclature and classification of carbohydrates into Mono, Di and Polysaccharides. Apply the system of classification and naming of Monosaccharides to identify and name a monosaccharide. Explain the isomers of monosaccharides i.e. the D and L isomers, Aldose - ketoses.  Definition  Carbohydrates (CHO) are single largest component of diet besides water, providing 48% of caloric need (i.e, Energy). In most CHO, the ratio of hydrogen to oxygen is 1:2:1. They are a group of organic compounds.  Functions of Carbohydrates 1. Supply the energy needs of the body. Glucose is the most important fuel for the cells 2. Serve as storage forms of energy. Eg: Starch and Glycogen. 3. Glycolipids and glycoproteins are important part of membrane structure and participate in functions like cell growth, adhesion and fertilization. 4. Carbohydrates also have special functions For eg: Ribose sugar is found in RNA, 5. Needed to oxidize fats completely and for synthesis of fatty acids and amino acids.  Carbohydrate Classification Carbohydrates are classified according to the number of sugar units. Monosaccharides: They contain one molecule of sugar and cannot be hydrolyzed into simpler carbohydrates. Disaccharides : They contain two monosaccharides linked together. Bonds linking carbohydrates are called glycosidic linkages. Oligosaccharides: Contain three to ten monosaccharide units linked together. Polysaccharides: Polymers of monosaccharides  Carbohydrate Classification 1. Monosaccharides: simple sugars; they can not be hydrolysed into simpler form and are further classified according to nomber of carbon atoms per molecule. a. Trioses: have 3 carbon atoms. Glyceraldehyde and dihydroxyacetone. b. Pentoses: have 5 carbon atoms. Ribose and ribulose. c. Hexoses: Have 6 carbon atoms. Glucose and fructose Dr. Zeinab Misbah 6  2 types of monosaccharide structures: Aldoses and ketoses. Monosaccharides CH OH 2 O │ ║ C=O ketose C─H aldose │ │ H─ C─OH H─ C─OH │ Mrs.Hanadi Filmban │ H─ C─OH H─ C─OH │ │ H─C─OH │ CH2OH CH2OH Erythose, an aldotetrose Fructose, a ketohexose 7 with a ketone group with an aldehyde group HEXOSES: 1. They all contain 6 carbon, 12 hydrogen and 6 oxygen (C6H12O6) 2. They may exist either in aldo or keto form. 3. Nutritionally important hexoses are glucose, galactose, mannose and fructose. Dr. Zeinab Misbah 8 Examples of the most important & common Monosaccharaides Dr. Zeinab Misbah 9 D-Glucose D-glucose is Found in fruits, corn syrup, and honey. An aldohexose with the formula C6H12O6. Mrs.Hanadi Filmban Known as blood sugar in the body. In blood, conc. Is 70-120 mg/dl Major building block of di- and poly saccharide and is transported by blood to all cells where its oxidized for energy. The monosaccharide in 10 polymers of starch, cellulose, and glycogen.  CH2OH D-Fructose C O HO C H D-Fructose is H C OH Is a ketohexose C6H12O6. Is the sweetest carbohydrate. H C OH Is found in fruit juices and CH2OH honey. It is also a component of D-Fructose sucrose. Galactose: Not found in nature as monosaccharide, but as a part of a disaccharide, lactose. Milk is the prime source of galactose. Mammary glands convert glucose to galactose then synthesize lactose.  Infants with Galactosemia lack the enzyme that convert the galactose to glucose which results in toxicity of galactose leading to mental retardation, liver damage. Treatment: All forms of milk and lactose be removed from the body. Dr. Zeinab Misbah 12  2- DISACCHARIDES: They are composed of 2 monosaccharide units, with same or different. Hydrolysis/ digestion C6H12O6 + C6H12O6 C12H22C11 + H2O Synthesis They account for 35% of dietary carbohydrates. Nutritionally important disaccharides are lactose, sucrose and Maltose. The 2 sugars are joined by an O-glycosidic bond. Dr. Zeinab Misbah 13 Important Disaccharides A disaccharide consists of two monosaccharides. Monosaccharaides Disaccharide glucose + glucose maltose + H2O Mrs.Hanadi Filmban glucose + galactose lactose + H2O glucose + fructose sucrose + H2O 14 Maltose Maltose is A disaccharide also known as malt sugar. Composed of two D-glucose molecules. Mrs.Hanadi Filmban Produced in the body by digestion of starch.. 15 LACTOSE: (milk sugar)  Major dietary CHO for infants.  It is found exclusively in the milk of mammals  10% of total CHOs consumed. Lactose is the only natural source of galactose.  Lactose is hydrolysed to its monosaccharides by lactase in humans and by β- galactosidase in bacteria.  Synthesized also during lactation.  Malabsorption (Lactose intolerance) leads to diarrhea, flatulence. Galactose is joined to glucose by a β-1,4-glycosidic linkage. Dr. Zeinab Misbah 16  Sucrose: Obtained from cane and beet commercially. Made of 2 monosaccharides glucose and fructose which are linked by a glycosidic linkage; α for glucose and β for fructose. It can be cleaved to its 2 components by enzyme sucrase. Sucrase/invertase Sucrose ----------------------> Glucose + Fructose Provides 20-30% of the total calories (i.e one of the energy source). Dr. Zeinab Misbah 17 Oligosaccharides:  represent carbohydrates that contain between 3 and 10 single sugar.  Common oligosaccharides include raffinose, stachyose and formed from: a tetrasaccharide consisting of two galactose units, glucose unit, and one fructose unit Some important Pentoses Ribose and Structural elements of nucleic acids and Deoxyribose Coenzymes(ATP, NAD etc)