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Lecture 12

BLG 151 Lecture 12: Chapter 12 notes

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Ryerson University
BLG 151
Martina Hausner

Microbiology Chapter 12: The Use of Energy in Biosynthesis 12.1 Principles Governing Biosynthesis Anabolism  Construction of cellular components from inorganic molecules and carbon source with the expenditure of stored energy – biosynthetic reactions – increasing order  Small molecules to large molecule  Energy from catabolism is used for biosynthetic pathways  Using carbon source and inorganic molecules, organisms synthesize new organelles and cells  Antibiotics inhibit anabolic pathways  A great deal of energy is needed for anabolism Anabolism – How Many Molecules Need To Be Made?  Turnover  Continual degradation/resynthesis of cellular constituents by nongrowing cells  Metabolism is carefully regulated  For rate of turnover to be balanced by rate of biosynthesis  In response to organism’s environment Principles Governing Biosynthesis  Macromolecules are synthesized from limited number of simple structural units (monomers)  Saves genetic storage capacity, biosynthetic raw material, and energy  Many enzymes do double duty  Many enzymes used for both catabolic and anabolic processes  Saves materials and energy  Catabolic and anabolic pathways are not identical as some enzymes function in only one direction Pathway Directions and Separations  To synthesize molecules efficiently, anabolic pathways must operate irreversibly in the direction of biosynthesis  Done by coupling breakdown of ATP to certain reactions in biosynthetic pathways  Drives the biosynthetic reaction to completion  Anabolic and catabolic reactions are physically separated  Located in separate compartments  Allows pathways to operate simultaneously but independently  Catabolic and anabolic pathways use different cofactors  Catabolism produces NADH (a substrate for electron transport)  NADPH used as electron donor for anabolism  Large assemblies (e.g. ribosomes) form spontaneously from macromolecules by self assembly 12.1 Precursor Metabolites: Starting Molecules for Biosynthesis Precursors Metabolites  Generation of precursor metabolites is critical step in anabolism  Carbon skeletons are used as starting substrates for biosynthetic pathways  Provide carbon skeletons as starting molecules for synthesis of monomers  Examples are intermediates of the central metabolic pathways  Most are used for the biosynthesis of amino acids  12 precursors: in chemoorgano-hetertrophs, these are produced by the central metabolic pathways. Autotrophs use CO2-fixation pathways and other pathways (e.g. gluconeogenesis) to make precursor metabolites  Carbon skeletons are used as starting substrates for biosynthetic pathways  Examples are intermediates of the central metabolic pathways  Most are used for the biosynthesis of amino acids 12.3 CO 2Fixation: Reduction and Assimilation of CO2Organic Carbon Calvin Cycle  Used by most autotrophs to fix 2O  Also called the reductive pentose phosphate cycle – reverse of pentose phosphate pathway  In eucaryotes, occurs in stroma of chloroplasts  In cyanobacteria, some nitrifying bacteria, and thiobacilli, may occur in carboxysomes  Must first convert CO t2 organic carbon before precursor metabolites can be formed  6 different CO 2fixing pathways known in microorganisms  The calvin cycle consists of 3 phases 1. The carboxylation phase 2. The reduction phase 3. The regeneration phase  During the carboxylation phase, enzyme ribulose 1,5=phosphate carboxylase/oxygenase (rubisco) adds CO t2 ribulose 1,5diphosphate, resulting in the formation of 2 molecules of 3 phosphoglycerate, which is reduced in the reduction phase to glyceraldehyde 3 phosphate  During the regeneration phase ribulose 5-phosphate is reformed so that the cycle can repeat  Three ATPs and two NADPHs are used during the incorporation of one CO 2 Summary 6CO +218ATP + 12NADPH + 12H + 12 H O + 2 + Glucose + 18ADP + 18Pi + 12NADP 12.4 Synthesis of Carbohydrates Synthesis of Sugars and Polysaccharides  Gluconeogenesis  Monosaccharides  Polysaccharides  Peptidoglycan Gluconeogenesis  Synthesis of glucose and related sugars from other precursors  Glucose, fructose, and mannose are gluconeogenic intermediates or made directly from them  Galactose synthesized with nucleoside diphosphate derivatives  Bacteria and algae synthesize glycogen and starch from adenosine diphosphate glucose  Functional reversal of glycolysis, but the two pathways are not identical  7 enzymes shared  4 enzymes are unique to gluconeogenesis Synthesis of Sugars  Gluconeogenesis is the production of glucose and related sugars from nonsugar precursors  Gluconeogenesis synthesizes fructose 6-phosphate, glucose 6 phosphate, and glucose. Once these sugars have been formed, other common sugars can be manufactured  Shares 7 of its steps with the Embden-Meyerhoff pathway – just the reverse  Four reactions are unique to this pathways 1. glucose 6-phosphatase 2. fructose bisphosphatase 3. phosphoenolpyruvate carboxykinase 4. pyruvate carboxylase Synthesis of Monosaccharides  several sugars are synthesized while attached to a nucleoside diphosphate such as uridine diphosphate glucose (UDPG) Synthesis of Polysaccharides  Polysaccharides are important structural components of cells (cell walls, storage compounds) and are biosynthesized from activated forms of their monomers (six-carbon sugars – hexoses, five-carbon sugars – pentoses – ribose, deoxyribose – RNA, DNA)  Synthesis of polysaccharides often involves nucleoside diphosphate  Example: during glycogen and starch synthesis in bacteria and protists, adenosine diphosphate glucose (ADP-glucose) is formed from glucose 1-phosphate and ATP. ATP + glucose 1-P  ADP-glucose + PPi It then donates glucose to the end of growing glycogen and starch chains (glucose)n+ ADP-glucose  (glucose) n+1 ADP Synthesis of Peptidoglycan Occurs in the Cytoplasm, at the Plasma Membrane, and in the Periplasmic Space  Large molecule made of chains of alternating
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