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BIO 330 Cell Biology Lecture Outline Spring 2011 Chapter 9: Glycolysis and Fermentation I. Metabolism A. Anabolic pathways Endergonic B. Catabolic pathways Exergonic Create metabolites II. ATP A. Phosphoanhydride bonds Hydrolysis splits 2nd bond Exergonic: G = -7.3 kcal/mol B. ATP/ADP Energy release / storage III. Chemotrophic Energy Metabolism A. Biological oxidation Removal of electrons (and protons, i.e., H atoms) Dehydrogenation / dehydrogenases B. Reduction Addition of electrons (and protons…) Hydrogenation / hydrogenases C. Redox reactions Oxidation and reduction happen simultaneously D. Electron acceptors Coenzymes NAD+ NADH E. Glucose oxidation Stepwise release of free energy G = -686 kcal/mol IV. Glycolysis and Fermentation A. Glycolytic pathway 10 reactions converting 1 glucose to two pyruvate molecules 3 phases Preparation and cleavage Add 2 phosphates to glucose via 2 ATP Hexokinase – 1st step; rate-limiting enzyme Phosphofructokinase-1 (PFK-1) (site of regulation) Aldolase – splits 1 6-C molecules into 2 3-C molecules Oxidation and ATP generation BIO 330 Cell Biology Lecture Outline Spring 2011 Substrate-level phosphorylation Phosphoglycerate kinase creates ATP NADH is produced Pyruvate formation and ATP generation Phosphoenolpyruvate hydrolysis by pyruvate kinase B. Pyruvate oxidation to Acetyl CoA In presence of oxygen Preparation for entry to Krebs cycle (citric acid cycle; tricarboxylic acid cycle) C. Fermentation In absence of oxygen Pyruvate is reduced by NADH to regenerate NAD+ Lactate fermentation Lactate dehydrogenase works in either direction depending on prevailing conditions in the cell Lactic acid produced in muscle is carried to liver and reincorporated into glucose via gluconeogenesis Lactic acid in bacteria can be used commercially for dairy products Alcoholic fermentation Pyruvate loses CO2 to become ethanol Pyruvate decarboxylase Alcohol dehydrogenase Alcoholic fermentation by yeast is used in baking and alcohol production No net oxidation occurs 2 ATP produced per glucose molecule V. Alternative Glycolysis Substrates A. Alternative substrates are converted to metabolic intermediates Proteins and lipids are converted to intermediates of the TCA cycle Carbohydrate substrates are converted to intermediates of glycolysis B. Other sugars and glycerol Fructose, galactose, mannose are common alternatives Polysaccharides and disaccharides are converted to monosaccharides Monosaccharides are converted to intermediates Pentoses must be converted to hexoses Phosphogluconate pathway (pentose phosphate pathway) Glycerol is converted to dihydroxyacetone phosphate C. Polysaccharides Phosphorolytic cleavage Similar to hydrolysis, using phosphate instead of water VI. Gluconeogenesis BIO 330 Cell Biology Lecture Outline Spring 2011 Synthesis of glucose from 3-C or 4-C precursors Similar to “reverse glycolysis” 3 very endergonic steps require different enzymes Bypass reactions G6Pase (glucose-6-phosphatase) FBPase (fructose-1,6-bisphosphatase) PEPCK (phosphoenolpyruvate) PC (pyruvate carboxylase) VII. Regulation of Glycolysis and Gluconeogenesis A. Spatial separation Glycolysis and gluconeogenesis occur in different cells / tissues B. Regulation Allosteric regulation of enzyme activity Glycolysis Hexokinase PFK-1 Pyruvat e kinase Gluconeogenesis FBPase Pyruvate carboxylase AMP and Acetyl CoA regulate both pathways C. Fructose-2,6-bisphosphate regulation of glycolysis and gluconeogenesis Phosphofructokinase (PFK) 2 is a bifunctional enzyme cAMP inhibits PFK 2 indirectly with regards to its kinase activity cAMP upregulates PKF 2 indirectly with regards to its phosphatase activity