Summary of Carbohydrate Structures

Summary of Carbohydrate Structures See original handout pages for the following: 1. Open chain and cyclic forms of monosaccharides 2. Disaccharide structures: maltose, sucrose, lactose 3. Shorthand structures of amylose, amylopectin (glycogen), and cellulose 4. Cyclization of aldoses and ketoses and rules for writing Hayworth projection formulas (“LURD”, “BUAD”) Chair Conformation of Pyranoses Fig 9-8 1 Reducing Sugars: Aldoses 6 HO Fig 9-10 O 5 OH 4 1 2 HO OH 3 OH α-D-glucopyranose 2 Cu+2 OHCu2O(s) OH- HO 6 5 4 O OH 1 O 2 HO Alkaline reagent with copper(II) chelator: Tartarate: Fehlings’s solution Citrate: Benedict’s solution 3 OH α-D-glucuronic acid lactone Reducing Sugars: Open Chain Ketoses! CH2OH C O HO C H OHH C OH H C OH CH2OH 1 2 3 4 5 6 O O CH H C OH HO C H H C OH H C OH CH2OH CH HO C H HO C H H C OH H C OH CH2OH 1 2 3 4 5 6 OPEN CHAIN FORM 1 2 + 2 Cu+2 Cu2O(s) 3 4 5 6 Ketose rearrances to mixture of aldoses which can be oxidized by Cu2+ reagents either as the open chain form or as the cyclic form 2 Functions of Monosaccharides Glyceraldehyde and dihydroxyacetone (C3): -Intermediates in glycolysis -Precursors for glycerol used for triglyceride and phosphoglyceride biosynthesis Ribose (C5): (CH2O)n partly oxidized, readily available energy source -Source of energy for plants and animals -Monomer unit for vitamin-derived coenzymes (NAD , FAD, etc) -Monomer unit for RNA + Ribofuranose in RNA and coenzymes NICOTINAMIDE ADENINE DINUCLEOTIDE ( B3 niacin(amide)) O H C O NH2 N - O P O O OH O OH NH2 N N N N - O P O O O OH OH **NAD (oxidized form) 3 Functions of Monosaccharides (CH2O)n partly oxidized, readily available energy source Glucose (C6): -Source of energy for plants and animals in glycolysis -Monomer unit for cellulose in plants Fructose (C6): -Source of energy for plants and animals in glycolysis HO HO HO DISACCHARIDES: Maltose Provides energy for maltose HO germinating seeds O O (breakdown product of HO OH O amylopectin and amylose OH OH in germinating seeds) O-α-D-glucopyranosyl-(1 -> 4)-α (or β)-D-glucopyranose (ending = "ose" since anomeric OH is free) Hydrolyzed into glucose by an enzyme called α-glucosidase 4 DISACCHARIDES: Sucrose sucrose HO Storage saccharide in… O HO glucose = α HO OH O HO …sugar beets O fructose = β HO …sugar cane OH OH Hydrolyzed into glucose and fructose by an enzyme called invertase O-α-D-glucopyranosyl-(1 -> 2)-β-D-fructofuranoside (ending = "oside" since anomeric O is derivatized) DISACCHARIDES: Lactose lactose HO O OH HO HO HO O O OH HO OH O-β-D-galactopyranosyl-(1 -> 4)-β -D-glucopyranose Found in milk, lactose provides energy to nursing infant Hydrolyzed by laccase = β-galactosidase 5 WRITING AMYLOSE POLYMER HO HO O O HO HO O HO O OH O OH OH Linear α-(1 ->4) linked polymer of glucose The reducing end of the polymer The nonreducing end (hemiacetal) of the polymer Fig 09-16.GIF THREE-DIMENSIONAL AMYLOSE ~ 20 D ~ 20 D 6 BIOLOGICAL FUNCTION OF AMYLOSE Amylose is a storage polymer for glucose in plants Q: How is the structure of amylose related to its biological function? A: The amylose polymer is a storage polymer for glucose. It has a helical structure which allows for more glucose to be packed into a given volume. HYDROLYSIS OF AMYLOSE: α-Amylase (in saliva and pancreatic juices of animals) (in plants and all other living organisms) α-Amylase is an endoglycosylase: It randomly hydrolyzes within the linear polymer (> 3) giving a mixture of maltose and glucose HO HO O O HO HO O O O OH OH Linear α-(1 ->4) linked polymer of glucose 7 HYDROLYSIS OF AMYLOSE: β-Amylase (in germinating seeds, sweet potatoes) β-Amylase is an exoglycosylase: It removes maltose units from the nonreducing ends of the amylose (> 4) HO HO O O HO HO HO O O O OH OH Linear α-(1 ->4) linked polymer of glucose The nonreducing end of the polymer How are Glycogen and Amylopectin Different? Polymer Glycogen 4-10 glucose/linear segments Amylopectin Occurance Function Liver, muscle Storage polymer for glucose Plants "" > 12 glucose/linear segments How are the structures of glycogen and amylopectin related to their biological function? 8 Periodate oxidation (lab) and methylation can determine degree of brancing METHYLATION OF GLYCOGEN VERSUS AMYLOPECTIN HO O OH O O branch point α (1 - 6) OH HO HO HO O O O OH OH O HO O OH O O O OH α (1 - 4) OH nonreducing end OH O OH linkages CH3I OH OH reducing end O OR CH3OSOCH3 O H+ Polymer I: Polymer II: 8.5 % 2,3 dimethyl glucose 2.1 % 2, 3 dimethyl glucose + what other products? (draw structural formulas for all products) Which polymer is glycogen and which is amylopectin and why? Enzyme that hydrolyze glycogen Polymer Glycogen Hydrolytic Enzymes Glycogen Phosphorylase gluc-(gluc)n + Pi
(gluc)n + gluc-1-Pi HO O OH O O branch point α (1 - 6) OH HO HO HO O O O OH OH O HO O OH O nonreducing end - O P OH O OH O OH α (1 - 4) linkages O OH OH OH O OH O reducing end - O 9 Enzyme that hydrolyze amylopectin Polymer Amylopectin Hydrolytic Enzymes Starch Phosphorylase gluc-(gluc)n + Pi
(gluc)n + gluc-1-Pi HO O OH O O branch point α (1 - 6) OH HO HO HO O O O OH OH O HO O OH O nonreducing end - O P OH O OH O OH α (1 - 4) linkages O OH OH OH O OH O reducing end - O What happens next with these branched polymer? 10 WRITING CELLULOSE STRUCTURE HO O O HO HO O OH HO Actual orientation of adjacent glucose residues: O O OH Linear β-(1 ->4) linked polymer of glucose Fig 9-17.GIF Linear fibers aggregate into sheets… Sheets aggregate into microfibrils… Microfibrils aggregate into stiff, rigid structures 11 What is the biological function of cellulose? Cellulose provides… 1. Structural ridigity to plants 2. Another polymer for glucose storage How is the structures of cellulose related to its biological function? What enzyme can hydrolyze cellulose? HO O O HO HO HO O HO HO O O O OH HO O OH O OH HO O OH 12