Biochemistry Lecture 2

Biochemistry Disaccharides & Sugar Derivatives LECTURE (2) DR. El-Sawy 0  Biochemistry...

Biochemistry Disaccharides & Sugar Derivatives LECTURE (2) DR. El-Sawy 0  Biochemistry Disaccharides & Sugar Derivatives Sugar acids Sugar alcohols Deoxy sugars Amino sugars Amino sugars acids A) Sugar Acids The oxidation products of monosaccharides Oxidation of Example  First aldehyde group  Gluconic acid is formed from glucose Aldonic acids to carboxylic group. by glucose oxidase enzyme.  Last hydroxyl carbon Uronic acids  D-glucuronic acid from glucose. to carboxylic group. Aldaric acids  Both carbonyl & last (Dicarboxylic  D-glucaric acid from D-glucose. hydroxyl carbon. acids)  6 carbon sugar acid.  It is water soluble & Optically active. L-ascorbic acid (vitamin C)  Must be supplied in the diet (essential vitamin).  Humans are unable to synthesize it. DR. El-Sawy 1  Biochemistry Disaccharides & Sugar Derivatives D) Amino-sugar B) Deoxy-sugars C) Amino-sugars acids  Monosaccharides  Hydroxyl group is  Condensation with one oxygen replaced by amino products of Formation missed (one OH group at C2 amino sugars & group replaced position. some acids. by H).  2Deoxy-D-ribose  D-glucosamine and  Neuraminic acid Example is a constituent of D-galactosamine. = mannosamine DNA. + pyruvic acid.  Glycosaminoglycans  Neural tissues Found in  Glycoproteins. DR. El-Sawy 2  Biochemistry Disaccharides & Sugar Derivatives E) sugar alcohols (Alditols) Def  They are the products of reduction of monosaccharides. 1. D-glucose → D-glucitol or D-sorbitol. 2. D-mannose → D-mannitol. 3. D-fructose → D-sorbitol or D-mannitol. 4. D-galactose → D-galactitol or D-dulcitol. 5. D-ribose → D-ribitol. 6. D-xylose → D-xylitol Examples DR. El-Sawy 3  Biochemistry Disaccharides & Sugar Derivatives Def :  2 monosaccharide units joined by O-glycosidic bond.  According to reduction : Non-Reducing Reducing  Both aldehyde/or  Either aldehyde or Def ketone groups are ketone group is free. involved in linkage Anomeric  Not free  Free carbon Example  Sucrose.  ‫الباقي‬ Types :  type of mono-saccharide: Homodisaccharides Heterodisaccharides  Same  Different Formed of monosaccharide monosaccharide MIC SULA  Maltose.  Sucrose. Example  Isomaltose.  Lactose.  Cellobiose  The most abundant disaccharides are : 1. Sucrose. 2. Lactose. SLM 3. Maltose. NB : DR. El-Sawy 4  Biochemistry Disaccharides & Sugar Derivatives Maltose Isomaltose Cellobiose Malt sugar Other name - - Maltose syrup Structure 2 α-glucose. 2 α-glucose. 2 β-glucose. Bond α 1-4 glycosidic. α 1-6 glycosidic. β 1-4 glycosidic. Reduction Reducing sugar By Hydrolysis Starch by Amylase. Dextran. Cellulose. of Maltose is hydrolyzed by maltase to give 2 glucose units Sucrose Lactose  Cane sugar  Table Milk sugar Other name  Beet sugar sugar [principal CHO in milk] Structure α-D-glucose & β–D-fructose β-D-galactose & β-D-glucose Bond α -1-β-2 glycosidic β 1-4 glycosidic Reduction Non-Reducing sugar Reducing sugar C carbon Not free Free  Hydrolyzed by sucrase  Hydrolyzed by intestinal lactase enzyme into glucose and into galactose & glucose. Hydrolysis fructose.  May appear in urine in late pregnancy & during lactation. DR. El-Sawy 5  Biochemistry Disaccharides & Sugar Derivatives Def :  Painful digestive upsets.  Low levels of lactase enzyme  Leads to undigested lactose  Lactose undergoes bacterial fermentation in colon  Etiology : Generation of large amounts of CO2, H2 and irritating organic acids. DR. El-Sawy 6  Biochemistry Disaccharides & Sugar Derivatives Hamed, a twenty six years old patient had been experiencing occasional discomfort after meals especially an hour after eating cheese and milk. He had abdominal cramps and diarrhea. His doctor advised him not to eat diary products. Q : What is the diagnosis ?  The case represents symptoms of lactose intolerance: 1. Abdominal discomfort after meals containing dairy products 2. Abdominal cramps. 3. Diarrhea.  Low levels of lactase leads to bacterial fermentation of the undigested lactose in the colon with the generation of large amounts of CO2 , H2 and irritating organic acids. DR. El-Sawy 7