Lecture 4 Carbohydrates PDF

Chemistry and Functions of Carbohydrates Dr. Abolanle A. A. KAYODE Senior Lecturer Department of Biochemistry School of Basic Medical Sciences Babcock University, Nigeria Types of Disaccharides  Reducing Disaccharides Lactose (Milk Sugar) Maltose (Malt...

Chemistry and Functions of Carbohydrates Dr. Abolanle A. A. KAYODE Senior Lecturer Department of Biochemistry School of Basic Medical Sciences Babcock University, Nigeria Types of Disaccharides  Reducing Disaccharides Lactose (Milk Sugar) Maltose (Malt Sugar, Product of Starch digestion)) Isomaltose (product of Starch digestion) Lactulose (Laxative) Cellobiose ( Product of Cellulose) Non Reducing Disaccharides Sucrose (Cane Sugar ) Trehalose  Lactose (Milk Sugar)  Components and Linkage of Lactose  Lactose is a Reducing Disaccharide β (1-4 ) glycosidic bond β D Galactose β D Glucose  Source / Occurrence Of Lactose Milk and Milk products. Lactating Mothers body.  Biomedical Importance Of Lactose Lactose has dietary and calorific value.  GIT enzyme Lactase digests Lactose by cleaving β (1-4) glycosidic bond and releases free Galactose and Glucose. Lactase deficiency in GIT leads to suffer from Lactose Intolerance. Certain bacteria can ferment lactose to lactic acid - souring of milk (Lactobacillus). Lactose may occur in urine during trimester of pregnancy.  Maltose  Maltose is a reducing Disaccharide Malt Sugar  Components and Linkage Of Maltose α D Glucose -α D Glucose α (1-4 ) glycosidic bond  Glucose to form Maltose + Condensation H2O Hydrolysis  Source / Occurrence Of Maltose Malt grain, Germinating seeds, Maltova. In human GIT, source of Maltose is through Starch and Glycogen digestion by α Amylase activity. Maltose is obtained in GIT as an end product of Starch and Glycogen digestion.  Biomedical Importance Of Maltose Maltose has dietary and calorific value. GIT enzyme Maltase digests Maltose by cleaving α (1-4) glycosidic bond and releases two Glucose units.  Isomaltose Isomaltose is a reducing Disaccharide. Isomaltose is a product of Starch and Glycogen digestion.  Components and Linkage Of Isomaltose α D Glucose -α D Glucose α (1-6 ) glycosidic bond Source /Occurrence Of Isomaltose In human GIT Isomaltose is obtained from Starch and Glycogen digestion by α-Amylase activity.  Biomedical Importance of Isomaltose Isomaltose has dietary and calorific value. Isomaltose is digested by GIT enzyme Isomaltase to release two Glucose units by cleaving α (1-6 ) glycosidic bond.  Cellobiose Cellobiose is a reducing Disaccharide. Disaccharide obtained from Cellulose Digestion.  Components and Linkage Of Cellobiose β D Glucose - β D Glucose β (1-4 ) glycosidic bond Source / Occurrence of Cellobiose Cellobiose obtained from Cellulose digestion In GIT of ruminants ( Cattle). Cellobiose is absent in human GIT, since enzyme Cellulase is absent which do not digest Cellulose.  Biomedical Importance of Cellobiose Cellobiose is absent in human beings. Not of biomedical Importance.  Lactulose Lactulose is a Reducing Disaccharide  Type, Components and Linkage of Lactulose β D Galactose -β D Fructose β (1-4 ) glycosidic bond Source / Occurrence Of Lactulose  In Plants Lactulose: Prepared by alkaline rearrangement of lactose  Biomedical Importance Of Lactulose Lactulose has therapeutic value; act as osmolar laxative. Relieves Chronic Constipation. Oral administration of Lactulose relieves hyper Ammonaemia in patients of Hepatic Encephalopathy.  Treatment of Systemic Encephalopathy By Lactulose.  Mechanism of action:  Lactulose is not digestible.  Bacterial flora convert it to Lactic and Acetic acids that irritate the intestinal wall.  Increases acidity of intestine ,this moves ammonia from blood to the intestine for neutralization.  Relieves Hyperammonaemia.  Sucrose  Sucrose is a Non Reducing Disaccharide  Cane sugar/ Common Table Sugar /Beet sugar  Components and Linkage Of Sucrose α D Glucose- β D Fructose  α 1- β 2 glycosidic bond. Why Sucrose is Non reducing? Glucose (C1) and Fructose(C2) anomeric carbon atoms are involved in formation of Glycosidic bond. No free anomeric carbon atoms. Hence Non reducing. Sucrose has no free aldehyde /ketone group hence non reducing Sucrose is dextrorotatory (d/+) with specific rotation 0 +66.5. Source /Occurrence Of Sucrose In Plants – Sugar cane, Beet root. Commercially prepared from sugar cane.  Invert Sugar Invert sugar is a product of Sucrose hydrolysis. Invert Sugar is a product of Inversion Process. Invert Sugar is a hydrolytic mixture of free Glucose and Fructose obtained from Sucrose hydrolysis.  Inversion process A non reducing and dextrorotatory Sucrose, on acid hydrolysis/by action of enzyme Invertase , Produces a hydrolytic mixture of 0 free, Glucose(+52.5 ) and Fructose(-930) which is reducing and laevorotatory(- 20.40). Invert Sugar is Reducing. Invert sugar is laevorotatory. (since Fructose has high magnitude of optical rotation -930) Invert Sugar is sweeter than Sucrose (since it contains free Fructose,a sweetest sugar)  Uses Of Invert Sugar Sweetening agent as it is more sweet than Sucrose. Used in adulteration of Honey. Biomedical Importance Of Sucrose Sucrose has dietary and calorific value. Sucrase or Invertase enzyme of GIT cleaves α 1- β 2 Glycosidic bond of Sucrose and release free Glucose and Fructose – i.e. Invert Sugar. Biomedically Important Oligosaccharides Oligosaccharides are composed of 3-10 Monosaccharide units linked by glycosidic bonds. Oligosaccharide may be branched or unbranched chain. Dietary Oligosaccharides are not digested by human hence has no calorific value. Oligosaccharides are components of Glycoproteins. Biomedically Important Polysaccharides/Glycans Polysaccharides are complex class of Carbohydrates, Chemically composed of more than ten, same or different Monosaccharide units or their derivatives Repeatedly linked by glycosidic linkages. General Formula of Polysaccharides (C6H10O5 )n Iodine test is a characteristic test for Polysaccharides Iodine test is based on Physical property of adsorption. Iodine get adsorbed on complex structure of Polysaccharides to give characteristic color.  Homopolysaccharides Homopolysaccharides are type of Polysaccharides composed of more than 10, same type of Monosaccharide units repeatedly linked by glycosidic bonds.  Glucosan Type of Homopolysaccharide Repeating unit,of Glucosan is Glucose Glucosan is a Polymer of Glucose.  Examples Of Glucosans Starch Glycogen Cellulose Dextrin Dextran  Fructosan Type of Homopolysaccharide Repeating unit in Fructosan is Fructose. Fructosan is a Polymer of Fructose. Example Of Fructosan Inulin  Starch Plant Homopolysaccharide  Chemistry Of Starch Starch is Glucosan Repeating Unit - α D Glucose (approx 7000)  Components of Starch- Amylose and Amylopectin  Amylose Amylose is 15-20% Linear structure α D Glucose linked by α (1-4) glycosidic bond.  CH2 OH CH2 OH CH2 OH CH2 OH H O H H O H H O H H O H H ( OH H H H O H OH H OH H OH H O O O O) H OH H OH H OH H OH amylose(-1,4 links)  Amylopectin  Amylopectin is 80-85 %  Branched structure  Branching point appears after every 25-30 Glucose units.  It has α (1-6) glycosidic bond at branching point.  α(1-4) glycosidic bonds in linear structure.  CH2 OH CH2 OH H O H H O H H ( OH H amylopectin O H OH H H OH O H OH O (-1,6 link) CH2 OH CH2 OH CH2 CH2 OH H O H H O H H O H H O H ( OHH H H H O H OH H OH H OH H O O O O) H OH H OH H OH H OH  Starch is white ,odourless, tasteless powder.  Starch is insoluble in cold water, but get solubilized on heating and form gel /paste.  Starch is a non reducing Carbohydrate. Starch -Negative Benedicts Test.  Starch on Iodine reaction gives blue color. Source/Occurrence Of Starch  Plants- Seeds, Tubers, Roots, Raw fruits.  Dietary Sources of Starch.  Grains- Rice ,Wheat, Jawar, Bajra  Potatoes  Beetroot.  Sago (Tapioca)  Vermicelli  Suji.  Raw Mangoes Biomedical Importance Of Starch Starch is a storage form of Glucose and serves as reservoir of energy in plants. To humans Starch is a predominant form of dietary Carbohydrate ingested through foods which has high dietary and calorific value.  Digestion of Starch  In mouth- by salivary α Amylase  In intestine -by pancreatic α Amylase  α Amylase cleaves, α (1-4) glycosidic bonds of Amylose and Amylopectin and releases Maltose and Isomaltose. Maltose and Isomaltose is then digested by Maltase and Isomaltase to release free Glucose units. Thus Starch on digestion gives thousands of free Glucose units which have high calorific value.