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Chapter 13 Chem 341 Suroviec Fall 2013 I. Overview • Glycolysis converts to two C3 units. The free energy released in this process is harvested to synthesize ATP from ADP and Pi I. Overview A. Some pathways are irreversible B. Catabolic and anabolic pathways MUST differ C. Every metabolic pathway has a 1st committed step II. Glucose A. Glucose • 6 carbon sugar with aldehyde group • form: OH group of the anomeric C is on OPPOSITE side of ring from CH2OH • form: OH group of the anomeric C is on SAME side of ring from CH2OH II. Glucose C. Glycogenolysis – Only liver can make glucose available to the liver at large III. Glycolysis • • Stage I. Energy investment – Glucose is phosphorylated and cleaved – Uses 2 ATP Stage II. Energy recovery – 2 molecules of glyceraldehyde-3phosphate converted to pyruvate – Produces 4 ATP IV. Reactions of Glycolysis A. Hexokinase Metabolically irreversible reaction B. Phosphoglucose Isomerase • Conversion of G6P to F6P C. Phosphofrutokinase • • PFK phosphorylates FBP Operates similar to hexokinase • • • Tetrameric enzyme R and T states in equilibrium ATP is both a substrate and and allosteric inhibitor C. PFK • • • Each PFK has 2 binding site – Substrate site – Inhibitor site Inhibitor site binds ATP only in T state Shifts equilibrium in favor of T at high ATP concentrations D. Aldolase • Catalyzes cleavage of FBP to form GAP and DHAP E. Triose Phosphate Isomerase • • • GAP continues down the glycolytic pathway DHAP and GAP are ketose-aldose isomers Final reaction Stage I F. Glyceraldehyde-3-Phosphate Dehydrogenase • • Exergonic reaction Synthesis of high energy 1,3-BPG G. Phosphoglycerate Kinase • • Bilobal with Mg2+ 1,3-BPG common intermediate whose consumption pulls reaction forward H. Phosphoglycerate Mutase • • • 3PG is converted to 2PG Phosphorylated His is needed to complete reaction 2,3-BPG allosteric inhibitor of deoxyhemoglobin I. Enolase • • • 2PG dehydrated to PEP Needs Mg2+ F- inhibitor of reaction J. Pyruvate Kinase • • • • PEP is cleaved via PK to form pyruvate Forms ATP Step 1: ADP nucleophilically attacks the PEP, forms ATP Step 2: Enolpyruvate tautomerizes to pyruvate 3 products of glycolysis • • • ATP – Investment of 2 ATP per glucose – Generation of 4 ATP NADH – Glucose oxidized – 2 NAD+ reduced to NADH – Electron transport Pyruvate – 2 molecules are produced – Complete oxidation to CO2 done in citric acid cycle III. Fermentation • Pyruvate – Aerobic conditions • completely oxidized to CO2 and H2O – Anaerobic conditions • converted to reduced end product to reoxidize NADH A. Homolactic Fermentation • • Demand for ATP high Supply of oxygen is low B. Alcoholic Fermentation • • Forms CO2, ethanol and NAD+ TPP is essential cofactor of pyruvate decarboxylase IV. Control of Glycolysis • • • Glycolysis operates continuously in most tissues Flux must vary to meet needs How do we determine to flux control mechanisms? • One 3 reactions of glycolysis potentially control it: – Hexokinase – Phosphofrucokinase – Pyrivate kinase