Carbohydrate Chemistry 1 PDF

CHEMISTRY OF CARBOHYDRATES Prepared by: Dr. Amany mohamed salah  OBJECTIVES By the end of the course, students should be able to: A1. Define the types, functions and isomerism of carbohydrates and importance of sugars and sugar derivatives. A2. Desc...

CHEMISTRY OF CARBOHYDRATES Prepared by: Dr. Amany mohamed salah  OBJECTIVES By the end of the course, students should be able to: A1. Define the types, functions and isomerism of carbohydrates and importance of sugars and sugar derivatives. A2. Describe general classification of carbohydrates A3. Point out polysaccharides and their location and functions  DEFINITION Carbohydrates (CHO) are aldehyde or ketone derivatives of polyhydric alcohols or any substances derived from them. SOURCES BIOMEDICAL IMPORTANCE  BIOMEDICAL IMPORTANCE 1. Most abundant dietary source of energy. 2. Also serve as storage form of energy –Glycogen. 3. Participate in the structure of cell membrane & cellular functions (cell growth, adhesion and fertilization). 4. Pentoses are important as part of DNA, RNA and several coenzymes. 5. Cellulose forms the cell walls of plants and is important in diet, preventing constipation. ‫إﻣﺳﺎك‬ 6. Mucopolysaccharides form the ground substance of mesenchymal tissues. 7. Certain carbohydrate derivatives are used as drugs, like cardiac glycosides / antibiotics.  ASSOCIATED DISORDERS ‫اﺿطراب‬ 1. Derangement in Glucose metabolism –Diabetes Mellitus. 2. Inherited deficiency of certain enzymes in metabolic pathways of different carbohydrates cause diseases. Glycogen storage disorders Galactosemia Hereditary fructose intolerence Lactose intolerance, etc.  CLASSIFICATION Carbohydrates are classified according to the hydrolytic products as follows: 􀁺 Based on number of sugar units present: Monosaccharides: Cannot be hydrolyzed further into simpler forms. Disaccharides: Yield 2 molecules of same or different monosaccharide units on hydrolysis e.g. sucrose, lactose and maltose. Oligosaccharides: Yield 3-10 molecules of monosaccharide units on hydrolysis. Polysaccharides: Yield more than 10 molecules of same or different monosaccharide units on hydrolysis.  Homo-& Heteropolysaccharides.  MONOSACCHARIDES 􀁺 Simplest group of carbohydrates, cannot be further hydrolyzed. 􀁺 Categorization of monosaccharides is based on: the Functional Group. (Aldehyde or keto). the Number of Carbon atoms.  MONOSACCHARIDES No of C-atoms Potentially active carbonyl group Trioses Tetroses Pentoses Aldoses Ketoses Hexoses Heptoses “These carbohydrates cannot Octoses be hydrolyzed into simpler compounds” Aldehyde CHO Ketone C O MONOSACCHARIDES BASED ON FUNCTIONAL GROUP  Trioses: These monosaccharides contain three carbon atoms. The smallest aldose in human body is glyceraldehyde and the smallest ketose in human body is dihydroxyacetone. glyceraldehyde dihydroxyacetone  Hexoses: These monosaccharides contain 6 carbon atoms. The physiologically important hexoses are glucose, galactose, fructose and mannose. pentose ‫اﻟﺗﺎﻟﺗﺔ ﺷﻣﺎااااااال‬ Glucose: It is the most important sugar of carbohydrates present in fruit juices and result from the hydrolysis of starch, cane sugar, maltose and lactose. Glucose is the sugar carried by the blood and is the principal sugar used by the tissues. It is the major source of energy. It is present in urine in cases of diabetes mellitus due to raised blood glucose. Fructose: It is present in fruit juices and honey. Fructose can be changed to glucose in the liver and intestine, so it can be used in the body. Fructose serves as the major energy source of spermatozoa. It provides the fuel for sperm while they are in seminal fluid. Fructose accumulation occurs in hereditary fructose intolerance. Galactose: It is formed during hydrolysis of lactose (milk sugar). Galactose can be changed to glucose and metabolized. It is synthesized in the mammary gland to make the lactose of milk. It is a constituent of glycolipids and glycoproteins. Galactosemia and cataract result from failure error of its metabolism. (4) Epimers: These are isomers differing in the configuration of the -OH and -H on carbon atoms 2, 3 and 4 of glucose. The most important epimers of glucose are mannose and galactose. Mannose is formed by epimerization at carbon 2 whereas, galactose by epimerization at carbon 4.  CARBON-2 EPIMERS H C O H C O H C OH HO C H HO C H HO C H H C OH H C OH H C OH H C OH CH2OH CH2OH D-GLUCOSE D-MANNOSE  CARBON-4 EPIMERS H C O H C O H C OH H C OH HO C H HO C H H C OH HO C H H C OH H C OH CH2OH CH2OH D-GLUCOSE D-GALACTOSE (5) Aldoses and Ketoses: Depending on the presence of aldehyde or keto group in the sugar. Fructose contains ketone group in position 2, whereas there is an aldehyde group in position 1 of glucose. Monosaccharides derivatives Sugar acids Sugar alcohols amino sugar Deoxy sugars  Sugar acids 1. Produced by oxidation of carbonyl carbon to carboxylic group. 2. Or by oxidation of last hydroxy carbon to carboxylic group. 3. Or by oxidation of both. 1.Aldonic CHO COOH H C OH H C OH HO C H bromine water, O2 HO C H H C OH H C OH H C OH H C OH CH2OH CH2OH D-Glucose D-Gluconic acid 2-Uronic CHO CHO H C OH H C OH HO C H H2O2 HO C H H C OH Dil. Nitric acid H C OH H C OH H C OH CH2OH 2 water exit COOH D-Glucose COOH remain D-Glucuronic acid Importance of Glucuronic acid It is a highly polar molecule which is incorporated into proteoglycans.( Hyaluronic acid, Heparin). Conjugated with bilirubin to form soluble conjugated bilirubin. An inability to conjugate bilirubin, as in hepatic disease , is a cause of jaundice. Conjugated with certain drugs in liver to increase their solubility. Glucuronate-conjugated drugs are more easily cleared from the blood by excretion in urine.  Sugar alcohols The sugar is reduced to the corresponding alcohol: 1. Glyceraldehydes give glycerol 2. Dihydroxyacetone give glycerol 3. Ribose → ribitol 4. Glucose → sorbitol 5. Galactose → galactitol 6. Mannose → mannitol 7. Fructose → a mixture of equal amounts of sorbitol & mannitol  CHO CH2OH H C OH H C OH H C OH H2 H C OH H C OH Na amalgum, H2SO4 H C OH CH2OH CH2OH Ribose Ribitol  CHO CH2OH H C OH H C OH HO C H H2 HO C H H C OH H C OH Na amalgum, H2SO4 H C OH H C OH CH2OH CH2OH Glucose Sorbitol  CH2OH CH2OH CH2OH C=O H C OH HO C H HO C H HO C H HO C H H2 H C OH OR H C OH H C OH Na amalgum, H2SO4 H C OH H C OH H C OH CH2OH CH2OH CH2OH Fructose Sorbitol Mannitol Importance of sugar alcohols They are used widely in the food industry as sweeteners. They are commonly used in place of table sugar (sucrose), often in combination with high intensity artificial sweeteners to counter low sweetness. Sugar alcohols are not metabolized by oral bacteria, and so they do not contribute to tooth decay. Ribitol is a part of the structure of vitamin B2 (Riboflavin),  amino sugar CH2OH CH2OH H O H H O H H H OH H OH H OH OH OH O OH H NH 2 H N C CH3 H -D-glucosamine -D-N-acetylglucosamine amino sugar - an amino group substitutes for a hydroxyl. An example is glucosamine. The amino group may be acetylated, as in N-acetylglucosamine.  Deoxy sugars D 2.deoxy ribose Is derived from D.Ribose by de-oxygenation at carbon–2. IT is found in DNA.  L-fucous Is derived from L-galactose by de-oxygenation at carbon–6.  DISACCHARIDES  These are sugars formed of 2 monosaccharide units linked by a glycosidic linkage.  The physiologically important disaccharides are maltose, sucrose and lactose. Reducing: Maltose, Lactose –with free aldehyde or keto group. Non-reducing: Sucrose, Trehalose –no free aldehyde or keto group. (1) Maltose: It is composed of 2 alpha D- glucose units united by alpha 1-4 glycosidic linkage. Maltose is found in germinating cereals and malt. It is produced during hydrolysis of starch by amylase. α-D-Glucose α-D-Glucose (2) Sucrose: It is called cane sugar or table sugar. Sucrose is formed by condensation of a molecule of alpha-D glucose with a molecule of beta-D fructose united by alpha 1-2 glycosidic linkage. It is dextrorotatory. On hydrolysis by the invertase (sucrase) enzyme, it yields a levorotatory mixture called invert sugar because the strong levorotatory of fructose inverts the previous dextrorotatory action of sucrose. ‫ علشان الفركتوز‬levoratatory ‫ بقت‬hydrolisis ‫ وبعد‬dextrorotatory ‫هي كانت‬ It is non-reducing sugar because the glycosidic linkage involves the carbonyl groups of fructose and glucose.  Sucrose α-D-Glucose β-D-fructose (3) Lactose (milk sugar): It is formed by condensation of a molecule of beta-D galactose with a molecule of beta D- glucose united by beta-1-4-galactosidic linkage. It is found in milk and may occur in urine during pregnancy. Lactose is hydrolyzed by the enzyme lactase. In lactase deficiency, malabsorption of lactose leads to diarrhea and flatulence. Least sweet sugar – 16% of sucrose. β-D-Galactose β-D-glucose  It is the most suitable sugar for baby feeding as a sweetener for milk because: 1. It is the least sweet sugar so that the baby can nurse a large amount of mother’s milk without getting his appetite lost. 2. It is non-fermentable sugar, so it does not form gases and not cause colic to the infant. 3. It has a laxative effect and prevents constipation and non-irritant to the stomach and does not induce vomiting. 4. It is the only natural source of galactose that enter in structure of galactolipids which are found in great amounts in brain and nerves  POLYSACCHARIDES Polysaccharides are formed by condensation of more than 10 monosaccharide units. They form colloidal solutions in water because they have high molecular weights. They are classified into 2 groups: (A) Simple or homopolysaccharides. (B) Mixed or heteropolysaccharides. (A) Homopolysaccharides: These are formed of only one type of sugar units. Homopolysaccharides include the following physiologically important carbohydrates: Starch Glycogen Cellulose Inulin Dextrans Chitin  Starch Main storage form of glucose in plants. It never exists in animals. Polysaccharide units Amylose (20—28%) and Amylopectin 72—80%) Polymer of α-D-glucose α-1 4 glycosidic linkage At branching points α-1 6 linkage No free aldehyde group Amylose Amylopectin Found in wheat, rice, corn, potatoes Starch granule Starch  B. Dextrins: Products of hydrolysis of starch and include amylodextrin, erythrodextrin, achrodextrin which form color with iodine. Used in IV infusions to increase blood volume in hypotension and circulatory failure.  Glycogen Glycogen is the chief storage form of carbohydrates in animals known as animal starch. Present in the liver and muscle. Both α-1 4 and α-1 6 linkages are found. More branched structure than starch. Gives red color with iodine. The glycogen tree is shorter and more branched (a branch point every 8-10 glucose units) than amylopectin. The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise. It is digestible because human amylases hydrolyze -glucosidic linkage.  Cellulose Cellulose is the chief constituent of the cell wall of plants. It is insoluble and consists of beta-D glucose units linked by beta (1-4) glycosidic bonds. It gives no color with iodine. Cellulose can not be digested by many mammals, including humans because of the absence of cellulase enzyme that attacks the beta- linkage, It increases the bulk of stool which increases the intestinal movement, preventing constipation. ‫االسهال‬ => (B) Heteropolysaccharides: These are polysaccharides formed of more than one type of simple sugar units. These include: glycosaminoglycans and glycoproteins. Mucopolysaccharides: Hyaluronic acid sulphate ‫الوحيد اللي مفهوش‬ Heparin Chondroitin sulphate Keratan sulphate Dermatan sulphate  B-Heteropolysaccharides They are polysaccharides that on hydrolysis produce several types of sugars. Mucopolysaccharides “Acid polysaccharides “ Glucoaminoglycans (GAG) Mucopolysaccharides are distributed in animal tissues either combined with proteins in the form of mucoproteins or in free form. They consist of chains of repeating disaccharide units of complex carbohydrates which are characterized by their content of aminosugars and uronic acids. glucose+NH2 in C.2 glucose but c.6 oxidated They enter in the structure of most tissues and are not oxidized to give energy. They give more than one kind of sugar on hydrolysis. The most important members are : mucopolysaccharides A-Sulfur-free mucopolysaccharides: Their sugar units are not sulfates, e.g., hyaluronic acid. B- Sulfur-containing mucopolysaccharides: Their sugar units are sulfated ,e.g.,chondroiten sulfate , Heparin Hyaluronic acid: - It is formed of beta Glucuronic acid + N- acetylglucosamine (without sulphate) Biochemical importance: It is present in connective tissue matrix, vitreous humor of the eye, in the skin, synovial fluid, around the ovum, and in the umbilical cord to preserve the full-form of these structures. – Function: Permitting migration during wound repair and morphogenesis, make cartilage compressible and acts as a lubricant in joints. B. Sulfur-containing mucopolysaccharides 1. Chondroitin sulfate: (Glucuronic acid + N-acetyl galactosamine sulphate). It occurs in the matrix of the connective tissues, cartilage, and bones. Function: in cartilage, it binds collagen and hold fibers in strong network, help to maintain the shape of skeletal muscles and have a role in compressibility of cartilage in weight bearing. 1. 1 2. Heparin: – (Glucuronic acid sulphate + glucosamine disulphate) – Heparin is anticoagulant (prevents blood clotting in vivo and in vitro. – It is produced by mast cells of connective tissues. (B) Glycoproteins: Glycoproteins are proteins containing carbohydrates in varying amounts ( 2-15 units which is usually branched). Carbohydrate content ≤ 10%. Proteoglycan References Course Notes: Lectures & labs Essential Book: Lippincott’s Illustrated Biochemistry Reviews (2017), 7th edition Recommended Book: Harper’s Illustrated Biochemistry (2018), 31st edition Periodicals, Web Sites: www.medscape.com, www.ekb.edu.eg