Lecture 15 Chapt 16 Glycolysis Living organisms like machines conform to the law of conservation of energy and must pay for all their activities in the currency of catabolism Ernest Baldwin Dynamic Aspects of Biochemistry Louie Pasteur s scientific investigations into fermentation of grape sugar were pioneering studies of glycolysis 1 OUTLINE Glycolysis First phase Reactions 1 5 no ATP generated Second Phase Reactions 6 10 generation of ATP Feeder pathway to glycolysis other sugars can also enter the glycolytic pathway Regulation of glycolysis Glucose transporters Fate of pyruvate under anaerobic conditions In yeast Alcohol fermentation In other microorganisms and exercising muscle Lactic acid fermentation Hypoxia Inducible Factor 2 Metabolic pathways are compartmentalized within cells Glycolysis pathway common to both prokaryotes and eukaryotes In eukaryotes glycolysis takes place in cytoplasm Phase 1 Phase 2 25 ATP 3 1st Stage of Glycolysis Uses 2 molecules of ATP glucose but makes no ATP Traps and prepares glucose for following oxidation steps Glucose is converted to glyceraldehyde 3 phosphate GAP 5 steps 1 Phosphorylation of glucose 2 Isomerization 3 Second phosphorylation of Fructose 6P 4 Cleavage into two 3 carbon molecules 5 Isomerization of DHAP to GAP 4 Glycolysis Reaction 1 Phosphorylation Mg ATP H2O ADP Pi glucose Pi G 6 P H2O glucose ATP G 6 P ADP G reaction 1 30 5 kJ mol G reaction 2 14 kJ mol G overall 16 5 kJ mol 5 Glucose is kept in the cell by phosphorylation to glucose 6phosphate 6 Hexokinase 7 Glycolysis Reaction 2 Isomerization by phosphoglucose isomerase 8 Glycolysis Reaction 3 Second Phosphorylation Phosphofructokinase PFK PFK1 9 Glycolysis Reactions 4 Cleavage of one 6 carbon to two 3carbon molecules 10 Glycolysis Reactions 5 end of 1st phase of glycolysis 11 Second Stage of Glycolysis The three carbon units are oxidized to pyruvate generating 4 molecules of ATP glucose and 2 NADH glucose GAP is converted to pyruvate 5 steps 6 Oxidation of GAP to 1 3BPG 7 Phosphorylation of ADP 8 Mutase 9 Dehydration by Enolase 10 Phosphorylation of ADP giving pyruvate 12 Glycolysis Reaction 6 GAP is oxidized to 1 3 BPG 13 Uncoupled Oxidation and Phosphorylation Reactions G 50 kJ mol 1 G 56 kJ mol 1 14 Coupling of the two processes by one enzyme allows the conservation of energy released by oxidation G 6 3 kJ mol 15 Molecules with High Phosphoryl Group Transfer Potential 16 Glycolysis Reaction 7 ATP producing reaction 2X glucose 2X glucose 2 ATP consumed in the 1st phase of glycolysis Reactions 1 and 3 are paid off in the this step of the 2nd phase of glycolysis 17 Thermodynamically favorable Reactions 7 drives the less favorable Reaction 6 Preparative step for ATP production in the following step GAP Step 6 G 6 3 kJ mol 1 3 BPG Compound with High Phosphoryl Group Transfer Potential G 49 6 kJ mol Actual ATP production Step 7 ATP 18 9 kJ mol 30 5 kJ mol 3 PG The formation of the high phosphoryl group transfe rpotential compound 1 3 BPG in step 6 is essential as a preparation for the ATP production in step 7 18 Glycolysis Reaction 8 Phosphoglycerate Mutase Note The term Mutase is applied to those enzymes that catalyze migration of functional groups from one position to another on the same substrate molecule 19 Glycolysis Reaction 9 Dehydration of 2 PG G 1 8 kJ mol 20 Molecules with High Phosphoryl Group Transfer Potential 21 Glycolysis Reaction 10 ATP synthesizing reaction Regulated step Pyruvate kinase Ketone form G 31 7 kJ mol after removing the energy used to phosphorylate ADP 22 The free energies of the reactions of glycolysis under standard state conditions G 23 The free energies of the reactions of glycolysis under actual intracellular conditions in erythrocytes G 96 kJ mol 1 G 24 The net reaction for glycolysis is G 96 kJ mol 1 25 Entry points in glycolysis for galactose and fructose 26 Fructose enters the glycolytic pathway in the liver through the fructose 1 phosphate pathway 27 Fructose can be converted to F 6P by hexokinase hexokinase 28 Galactose enters the glycolytic pathway in the liver through the glucose 6 phosphate pathway 29 Glycosyltransferase Reaction phosphoglucomutase G 6P glycolysis 30 Regulation of Glycolysis is Cell Type Dependent Liver uses glucose to maintain blood sugar level Muscles use glucose for fuel ATP to power muscle contraction 31 Regulation of Glycolysis hexokinase phosphofructokinase pyruvate kinase Enzymes catalyzing irreversible reaction in metabolic pathways are potential control sites 32 Hexokinase versus Glucokinase Muscle contains Hexokinase I while liver contains Hexokinase IV Glucokinase This is to adapt to the different roles of muscle and liver Vmax 2 Km hexokinase 0 03 mM Km glucokinase 10 mM X normal blood sugar X 33 Regulation of Glycolysis Hexokinase Phosphofructokinase PFK PFK 1 Pyruvate kinase Enzymes catalyzing irreversible reaction in metabolic pathways are potential control sites 34 Glucose 6 P is common to several metabolic pathways Hexokinase PFK 35 Regulation of Allosteric Enzymes by feedback Mechanism Negative Feedback Inhibition e X 1 e2 e3 e4 e5 W X Y Z A B C D E F Positive FeedFeedback forward activation Committed step 36 Regulation of Phosphofructokinase In muscles PFK PFK1 37 Allosteric Regulation of Phosphofructokinase High AMP Low AMP ATP is an allosteric inhibitor of PFK AMP competes off ATP inhibition of PFK 38 Regulation of Phosphofructokinase PFK PFK1 In muscles PFK In liver 39 Fructose 2 6 bisphosphate Under hormonal I G regulation 40 The activation of phosphofructokinase by fructose 2 6 bisphosphate 41 PFK 42 Regulation of Glycolysis hexokinase phosphofructokinase pyruvate kinase Enzymes catalyzing irreversible reaction in metabolic pathways are potential control sites 43 Regulatory mechanisms of pyruvate kinase In muscles M form and liver L form ATP ATP In liver only L Protein Kinase A PKA AcetylCoA Alanine 44 The control of the catalytic activity of liver L form pyruvate kinase Covalent modification cAMP dependent protein kinase A PKA PEP 45 The regulation of glycolysis in the liver corresponds to the biochemical versatility of the liver Regulates blood sugar levels PFK and PK Uses glycolytic intermediates as substrates in other pathways PFK and PK In muscle glycolysis is regulated to meet the energy needs of contraction 46 In muscle glycolysis is regulated to meet the energy needs of contraction 47 2 1 48 1 2 49 Normal serum glucose concentration is 4 8 mM 50 Glycolysis helps pancreatic cells sense
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