Carbohydrates Lecture Notes PDF

 Definition Carbohydrates literally mean hydrates of carbon. carbon and hydrates ( water). Because it was thought to have the molecular formula (CH2O)n, the ratio of H to O as in water (H2O) hence the name. Now known that not all carbohydrates obey this rule. (e.g,derivative) ...

 Definition Carbohydrates literally mean hydrates of carbon. carbon and hydrates ( water). Because it was thought to have the molecular formula (CH2O)n, the ratio of H to O as in water (H2O) hence the name. Now known that not all carbohydrates obey this rule. (e.g,derivative)  Biochemical Definition Carbohydrates are poly-hydroxy carbonyl compounds (aldehyde or ketone) and their derivative and the polymer that give them on hydrolysis Example:  BIOMEDICAL IMPORTANCE  Carbohydrates have important structural and metabolic roles.  Glucose is the most important carbohydrate most dietary carbohydrate is absorbed into the blood stream as glucose.  Glucose is the major metabolic fuel of mammals a universal fuel of the fetus Biomedical Importance of Carbohydrates 1- Energy source for plants and animals (glucose). One of the major source of energy in cell. 75% of energy in cell comes from CHO. 25% from others (fats) 1 g CHO =4 K.calories 1 g protein =4 K.calories. 1 g lipid =9K.calories. Why body not use lipid as major energy source instead of CHO? 2- Cell membrane components: eg. Glycolipid and glycoprotein 3- Form structural tissues in plants and in microorganisms eg. (cellulose, chitin, murein) 4- Glucose is the precursor for synthesis of all other carbohydrates in the body, including Galactose in lactose of milk. Glycogen for storage;. Store as glycogen in animals, and starch In plants. (storage form of energy). Why the cell store excess glucose as glycogen? Ribose and Deoxyribose in nucleic acids; DNA –deoxy ribonucleic acid (deoxy sugar) RNA –ribonucleic acid (ribose sugar).. 5-To describe the mechanism of some diseases related to CHO. eg.Diabetes Mellitus. lactose intolerance, Glycogen storage diseases glactosemia. ,  Classification of Carbohydrates Carbohydrates are classified into four groups: 1.Monosaccharides: (saccharides means sugars)that cannot be hydrolyzed into simpler carbohydrates, (Exp. Glucose). 2.Disaccharides: condensation products of two monosaccharide units (Exp. Lactose). Note, all mono and disaccharides have the ending ose (glucose, galactose, ribose, lactose, etc…) Classification of Carbohydrates 3.Oligosaccharides are condensation products of three to ten monosaccharides; Maltotriose is an example. 4.Polysaccharides are condensation products of more than ten monosaccharide units (Exp. Glycogen & Starch). Monosaccharides are classified by: 1- the number of carbon atoms: 3C-Triose , 4C -tetroses , 5C-pentoses , 6C- hexoses and 7C – heptoses. 2-the position or type of carbonyl group: Aldehyde, aldose (terminal) Ketone, ketose (middle ). 3- Both number of carbon atom and type of carbonyl E,g Aldotriose and Ketotriose Monosaccharides are classified by: 1- the number of carbon atoms:  Aldose sugars H H H H H C O C O C O C O C O (H C OH)n H C OH H C OH H C OH H C OH CH2OH CH2OH H C OH H C OH H C OH Aldose Aldotriose CH2OH H C OH H C OH n=1 Aldotetrose CH2OH n=2 H C OH Aldopentose CH2OH n=3 Aldohexose n=4 Ketose sugars CH2OH CH2OH CH2OH CH2OH C O C O CH2OH C O C O (H C OH)n H C OH C O H C OH CH2OH CH2OH H C OH H C OH CH2OH CH2OH H OH Ketose Ketotriose Ketotetrose n=1 Ketopentose H C OH n=0 n=2 CH2OH Ketohexose n=3  Monosaccharides Glucose Structure The structure of Glucose can be represented in three ways: Straight Chain Form Haworth Projection Chair Form  Cyclic Fischer Haworth Projection Projection of a-D- of a-D-Glucose Glucose Almost all monosaccharides (except  dihydroxy acetone DHA )contain at least  one asymmetrical carbon atom (chiral centre) and are, therefore,have optical activitity (ability to rotate plane polarized light) and optical isomers. The number of isomers is obtained by the  formula 2n n=No of asymmetric carbons atom.  Monosaccharides Forms of Isomerism Monosaccharides exhibit various forms of isomerism: Because it have asymmetric carbon atom D and L Enantiomers. Pyranose and Furanose ring structures. Alpha and Beta anomers. Epimers. Aldose and Ketose isomerism. Optical activity  1- D & L isomers (enantiomers) Those monosaccharides that are of physiological  significance exist in the D-configuration, where the hydroxyl group is on the right side. The mirror-image, called enantiomers, are in the L- configuration. They are related to glyceraldehyde which exists in  two isomers D and L  Monosaccharides L and D Enantiomers It also called mirror images or Optical Isomers: Monosaccharides can exist in  either of two configurations, as determined by the orientation of the hydroxyl group about the asymmetric carbon farthest from the carbonyl group. e,g D & L form of glucose is  determine by carbon 5.  Monosaccharides L and D Enantiomers 2-pyranose and furanose ring (isomer) Monosaccharide with 5 or 6 carbon atoms tend to cyclyze in solution. This terminology indicate that the ring structure of monosaccharide is similar to either pyran or furan  Monosaccharides 2-Pyranose and Furanose  3 - α- and β anomers.(isomers) Isomers that differ on the position of OH group around anomeric carbon (which was carbonyl carbon) when the ring is formed.  Monosaccharides 3-Alpha and Beta Anomers  3-EPIMERS (ISOMERS) Two monosaccharide that differ from each other by position of OH group on one carbon. ( eg carbon 2,3 and 4 of glucose). glucose and glactose ar epimers at carbon 4 While glucose and mannose are carbon 2 epimers.  Monosaccharides Epimers Mannose Glucose Galactose  Monosaccharides 5-Aldose and Ketose Isomerism Optical activity The ability to rotate plane-polarized light to the right (dextrorotatory) +sign Or to the left (levorotatory) - sign Glucose is dexrtoratotry hence the name dextrose in clinical practice eg IV fluid Fructose is levorotatory hence the name levulose  Monosaccharides Physiological Importance  Pentoses of Physiologic importance Ribose inter the structure of Nucleic Acids Ribose Deoxyribose  Monosaccharides Physiological Importance Hexoses of Physiologic importance:  Glucose.  Fructose  Galactose.  D-glucose Common names: glucose, grape sugar, dextrose Natural Source: Fruits,,cereal starch hydrolysis, sugar hydrolysis, corn syrup and honey. Importance: the sugar of the body, the principal one used by the tissue. Building block for: disaccharides (such as sucrose, lactose and maltose) and polysaccharides (starch, cellulose and glycogen) converted to ribose and deoxyribose for DNA and RNA synthesis.  D-galactose Natural Source: None for free form Formed by hydrolysis of lactose (milk sugar). Importance: converted to glucose, and used for the synthesis of Milk. enter in cellular membranes of brain & nervous system. Deficiency diseases: Galactosemia: Enzyme to metabolize galactose missing and levels build in blood cause mental retardation, cataracts and cirrhosis.  D-fructose Common names: Levulose and fruit sugar Natural Source: Fruit juice and honey Hydrolysis of cane and beat sugar Importance: converted to glucose in liver, source of energy for spermatozoa Due to sweetness, used as sweetener.  Monosaccharides derivative 1-Amino sugar (replacement of one hydroxyl group by amino group e.g, glucose amine (in glycoprotein and glycolipid and glycosaminoglycan a heteropolysaccharide erythromicine(antibiotic) 2- Phosphate ester in metabolism. 3- Oxidation of glucose at carbon one give (aldonic) gluconic acid this is the bases of Benedict and Fehling ,reaction in detection of glucose in urine the sugars are called reducing sugar. When the anomeric cabon form bond with another molecule the sugar is non reducing. while oxidation at carbon 6 give (uronic) glucuronic important in detoxification reaction and in glycosaminoglycan a heterpolysaccharide 4- Reduction of glucose at carbon one give sugar alcohol sorbitol (which in high level as in diabetic leads to cataract formation)  Glycosides Glycoside is two substances connected by glycosidic bond. Importance: 1- formation of disaccharide and other derivative. 2- cardiac glycoside (is a drug used in treatment of some heart disease)by inhibiting Na-K ATPase pump. e.g Digitalis &.Auobain (contain sugar and steroid) 3-Certain antibiotic like streptomycin.  Disaccharides The physiologically important disaccharides are Maltose , Sucrose, and Lactose: Disaccharides Formation  Disaccharides Maltose Maltose : Malt sugar, composed exclusively of glucose, found in germinating cereals and malts The major degradation product of starch, is composed of 2 glucose monomers in an α-(1,4) glycosidic bond.. Give Glucose + glucose by maltase enzyme.. Disaccharides Maltose  Disaccharides Sucrose Sucrose: table sugar, found in cane and beat sugar composed of glucose and fructose through an α-(1,2)b-glycosidic bond. give Glucose + fructose by sucrase enzyme(invertase) because the product of its hydrolysis (known as invert sugar) invert optical activity from dextro to levorotatory. Disaccharides Sucrose  Disaccharides Lactose Lactose: Milk sugar , is found exclusively in the milk of mammals and consists of galactose and glucose in a β-(1,4) glycosidic bond give Glucose + galactose by lactase enzyme Disaccharides Lactose Lactose Intolerance Symptoms Bloating, abdominal discomfort, and diarrhea Causes Lactase deficiency Oligosacchrides Usually not found free but in the form of glycoprotein and glycolipid.few e,g maltotriose and raffinose. Sucrose: prevalent in Lactose: is found sugar cane and exclusively in the sugar beets, is milk of mammals and composed of consists of galactose glucose and fructose through an α-(1,2)b- and glucose in a β- glycosidic bond. (1,4) glycosidic bond Maltose: the major degradation product of starch, is composed of 2 glucose monomers in an α- (1,4) glycosidic bond.  Classification of polysaccharide When polysaccharides are composed of a single monosaccharide building block, they are termed homopolysaccharides. They are Branched or unbranched Storage or structural Polysaccharides composed of more than one type of monosaccharide are termed heteropolysaccharides Polysaccharides Types  Polysaccharides Starch  Is a homopolymer of Glucose. (storage form of CHO in plant)  It is the most abundant carbohydrate in cereals, potatoes, and other vegetables.  The two main constituents are amylose (15–20%), which has a non-branching helical structure.  and amylopectin (80–85%), which consists of branched chains composed of 24–30 glucose residues united by 1 → 4 linkages in the chains and by 1 → 6 linkages at the branch points.  Polysaccharides Starch (Amylopectin)  Polysaccharides Glycogen  Is the storage polysaccharide in human.  Is a highly branched than amylopectin Glycogen is the major form of stored carbohydrate in animals. It is a homopolymer of glucose in α-(1,4) linkage; it is highly branched, with α-(1,6) branch linkages occurring every 8-11 residues. Glycogen is a very compact structure. This compactness allows large amounts of carbon energy to be stored in a small volume, with little effect on cellular osmolarity. Glycogen is primarily stored in liver and muscles. Liver glycogen contributes to maintenance of blood glucose level Muscle glycogen is used as readily available source of energy within muscles during exercise  Polysaccharides Glycogen (General Structure)  Polysaccharides Glycogen (Branch Point)  Polysaccharides Others Inulin is a homopolysaccharide of fructose, linked by β(1-2) glycosidic bond.  found in tubers and roots of artichoke ( used for assessment of glomerular filtration rates.  Cellulose: is the chief insoluble constituent of plants framework.  It consists of β-D-glucopyranose units linked by β(1 → 4) bonds to form long, straight chains.  Cellulose cannot be digested by human because of the absence of an enzyme that hydrolyzes the β linkage.  There is limited bacterial metabolism of cellulose in the human colon  It is an important source of “bulk” and Fibers in the diet (which attract water and soften stool hence prevent constipation) Heteropolysaccharide Polysaccharides composed of more than one type of monosaccharide are termed heteropolysaccharides E.g,Heparin (anticoogulant) Hyluronic acid Keratan and Dermatan sulfate in extracellular matrix of connective tissue and synovial fluid