PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Glucose-6-P is common to several metabolic pathwaysSlide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43• 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 fermentationIn other microorganisms and exercising muscle: Lactic acid fermentation• Hypoxia-Inducible Factor1Lecture 15 (Ch. 16) – Glycolysis2Phase 1Phase 2~25 ATPGlycolysis in prokaryotes, archaea & eukaryotesEukaryotic glycolysis occurs in the cytoplasmMetabolic pathways are compartmentalized in cellsGlucose is converted to glyceraldehyde 3-phosphate (GAP)5 steps: 1. Phosphorylation of glucose2. Isomerization 3. Second phosphorylation of Fructose-6P4. Cleavage into two 3-carbon molecules5. Isomerization of DHAP to GAPUses 2 molecules of ATP/glucose but makes no ATP. Traps and prepares glucose for following oxidation steps31st Stage of GlycolysisMg2+4ATP + H2O ADP + Pi∆G°’reaction 1 = -30.5 kJ/molglucose + Pi G-6-P + H2O ∆G°’reaction 2 = +14 kJ/molglucose + ATP G-6-P + ADP ∆G°’overall = -16.5 kJ/molGlycolysis Step 1: Phosphorylation5HexokinaseGlucose is kept in the cell by phosphorylation to glucose-6-phosphate67Glycolysis Step 2: Phosphoglucose IsomeraseGlucose-6-phosphate (G-6P)Fructose-6-phosphate (F-6P)G6P is difficult to split into 3-carbon products. F6P is easier to convert.8Phosphoglucose Isomerase: MechanismGlycolysis: Reaction 3- Second Phosphorylation9Glycolysis: Reactions 4 – Cleavage of one 6-carbon to two 3-carbon molecules10Fructose 1,6-bisphosphateALDOLASE•Readily reversible by Aldolase•Both products need to be G3P for next stepGlycolysis: Reactions 5 - end of 1st phase of glycolysis11•90% at equilibrium•G3P is taken up by next stepGlyceraldehyde 3-Phosphaate (G3P) is converted to pyruvate:5 steps: 6. Oxidation of G3P to 1,3BPG7. Phosphorylation of ADP8. Mutase9. Dehydration by Enolase10. Phosphorylation of ADP, giving pyruvateGlyceraldehyde 3-Phosphaate (G3P) is converted to pyruvate:5 steps: 6. Oxidation of G3P to 1,3BPG7. Phosphorylation of ADP8. Mutase9. Dehydration by Enolase10. Phosphorylation of ADP, giving pyruvateSecond Stage of GlycolysisThe three carbon units are oxidized to pyruvate, generating 4 molecules of ATP/glucose and 2 NADH/glucose12Glycolysis Reaction 6 – G3P is oxidized to 1,3-BPG13(GAPDH)•Transfer Hydride from donor to NAD+ or from NADH to acceptor molecule•Conversion of aldehyde to carboxylic acid before phosphorylation (2 step process)∆G°’ = -50 kJ mol-1∆G°’ = ~ +56 kJ mol-1Uncoupled Oxidation and Phosphorylation Reactions14aldehyde Carboxylic acid•Transfer Hydride from donor to NAD+ or from NADH to acceptor molecule•Conversion of aldehyde to carboxylic acid before phosphorylation (2 step process)Requires Thioester intermediate15Oxidizing reagentG3P Dehydrogenase MechanismNicotinamide adenine dinucletideThioesterThiohemiacetalPi attacks + carbonyl•Thioester is higher energy than carboxylic acid.Cannot resonateLess stable (easier cleavage)Coupling of the two processes (by one enzyme) allows the conservation of energy released by oxidation∆G°’ = +6.3 kJ/mol16Glycolysis: Reaction 7 (ATP producing reaction)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.2 per glucose17•Substrate level phosphorylation = phosphate donor is kinase substrate•Not a phosphatase because Pi is not generated as free molecule18Phosphoglycerate Kinase MechanismThe formation of the high-phosphoryl group transfer potential compound 1,3-BPG (in step 6) is essential as a preparation for the ATP production (in step 7).Preparative step for ATP production in the following stepATPStep 6Step 7Actual ATP productionThermodynamically favorable Reaction 7 drives the less favorable Reaction 6∆G°’ = +6.3 kJ/mol∆G°’ = -49.6 kJ/mol30.5 kJ/mol19Compound with High-Phosphoryl Group Transfer PotentialGAP1,3-BPG3 PG-18.9 kJ/molGlycolysis: 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)20Glycolysis: Reaction 9 - Dehydration of 2-PG2122Ketone form ΔG°′ = -31.7 kJ/mol after removing the energy used to phosphorylate ADP ΔG°′ = -31.7 kJ/mol after removing the energy used to phosphorylate ADPPyruvate kinaseThe net reaction for glycolysis∆G°’= - 96 kJ/mol23Glucose + 2Pi + 2ADP + 2NAD+ 2 pyruvate + 2ATP + 2NADH + 2H+ + 2H2OEntry points in glycolysis for galactose and fructose.24hexokinaseFrom Lactose ->From Sucrose ->•There are no dedicated pathways for other monosaccharides•Other sugars must be converted to glycolysis intermediates2 pathwaysFructose enters the glycolytic pathway in the liver through the fructose 1-phosphate pathway.25Galactose enters the glycolytic pathway in the liver through the glucose 6-phosphate pathway.26GlucoseGlycosyltransferase ReactionG-6Pphosphoglucomutaseglycolysis27UDP-glucoseRegulation of GlycolysisEnzymes catalyzing irreversible reaction in metabolic pathways are potential control sites1. hexokinase2. phosphofructokinase3. pyruvate kinase28Muscle contains Hexokinase I while liver contains Hexokinase IV (Glucokinase). This is to adapt to the different roles of muscle and liver. 1 – Hexokinase versus GlucokinaseVmax 2Km (hexokinase)= 0.03 mMKm (glucokinase) = 10 mMX= normal blood sugarX29•Liver uses glucose “left over” from brain and muscle Hexokinase•Liver uses glucose for glycogen storage•G6P does NOT feed back to inhibit GlucokinaseGlucose-6-P is common to several metabolic pathwaysPFKHexokinase3031Glucose G6P F6PGlycogenF1,6BP ATPHKPFKCommitmentStep•If G6P feeds into PFK, then PFK activity can affect HK -> Eliminates repressor•If PFK is off, then G6P and F6P are at equilibrium -> G6P fed to Glycogen pathway•>> Inhibition of PFK can inhibit
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