Transcript Lecture 19
Metabolism and Sugars 4/2/03 Carbohydrate and sugar structure Carbohydrates or saccharides are essential components of living organisms. (C•H2O)n Where n=3 or greater. A single saccharide is called a monosaccharide. Oligosaccharide is a few linked monosaccharides and are at time associated with proteins (glycoproteins) or lipids (glycolipids) Polysaccharides consist of many monosaccharides i.e. cellulose or glycogen Monosaccharides (D-aldoses) The Fischer convention, the basis for the Dconfiguration in sugars comes from D-glyceraldhyde’s configuration around its asymmetric carbon. 1 CHO H HO H H 2 3 4 5 1 CHO OH H H HO 2 3 OH H 4 OH H OH HO OH 5 H 6 CH 2OH 6 D-glucose L-glucose CH 2OH Epimers differ in configuration around one carbon atom i.e. Dglucose and D-mannose but D-glactose and D-glucose are not epimers because they very around two carbon atoms. There are 2n-2 stereoisomers Carbohydrates are classified as to the nature of the carbonyl group : ketone = ketose aldehyde = aldose Triose 2(n-3) stereoisomers of ketoses Tetrose Pentose Hexose Monosaccharides can form ring structures O Furan O Pyran Glycosidic binds are between two sugars They can either be in the a or b configuration and can be linked through the 1-2, 1-4 or 1-6 linkage Sugar Polymers The Polysacchrides • Energy Storage – Starch a-amylose and amypectin • Structural – Cellulose and Chitin • Glycosaminoglycans • Proteoglycans a-amylose Cellulose (polyglucose) Glycosaminoglycans & Proteoglycans Bacteria Cell Walls Peptidoglycan Metabolism Metabolism is the overall process through which living systems acquire and utilize free energy to carry out their functions The coupling of exergonic reactions of nutrient breakdown to the endergonic processes is required to maintain the living state How do living things acquire the energy needed for these functions? Phototrophs- acquire free energy from sunlight Chemotrophs - oxidize organic compounds to make ATP ATP is the energy carrier for most biological reactions A road map of metabolic pathways. Metabolic pathways A series of consecutive biochemical reactions catalyzed by enzymes that produce a specific end product. Catabolism- the breakdown of food stuffs to simple organic chemicals. Anabolism- the synthesis of biomolecules from simple organic chemicals. The breakdown of foods converge to a few simple compounds. Very Few metabolites are used to synthesize a large variety of biomolecules •Acetyl-Coenzyme A (acetyl-CoA) •Pyruvate •Citrate acid cycle intermediates Three main pathways for energy production •Glycolysis •Citric acid cycle •Oxidative-Phosphorylation Certain pathways are involved in both breakdown and buildup of molecules these pathways are called amphibolic. The citric acid cycle is an example of this. Metabolic pathways are irreversible They have large negative free energy changes to prevent them running at equilibrium. If two pathways are interconvertible (from 1 to 2 or 2 to 1), the two pathways must be different! Independent routes means independent control of A rates. 2 1 Y X The need to control the amounts of either 1 or 2 independent of each other.