Lecture 4 Carbohydrates PDF
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Babcock University
Dr. Abolanle A. A. KAYODE
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Summary
This lecture covers the chemistry and functions of carbohydrates, specifically focusing on disaccharides such as lactose, maltose, isomaltose, cellobiose, and sucrose. It also discusses invert sugar and the biomedical importance of each type.
Full Transcript
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.