Free energy changes in glycolysisGlucosePyruvateOtherstepshaveG~0Near-equilibriumreactionsCanaccommodatefluxineitherdirectionDirection controlledbyconcentrationsof substratesandproducts
Other steps have ΔG ≈ 0 Near-equilibrium reactions Can accommodate flux in either direction Direction controlled by concentrations of substrates and products (mass action ratio) Free energy changes in glycolysis
First Phase of glycolysisFinal product C=0CH3CH,OHPyruvateGlucose4ATP1hexokinaseADP10,POCHGlucose-6-phosphateAdd@2phosphoglucoseisomerase HoAGOHFructose-6-phosphate2O,POCHCH,OHEnergyATPInvestmentChangeOH3phosphofructokinasePhaseADPformFructose-1,6-bisphosphate-30,POCHCH,OPO}Add@OH4aldolaseHOGlyceraldehyde-Dihydroxyacetone.H+CH,OPO,3-phosphatephosphatecoOHHSplit5triosephosphateisomeraseCH,OPO)CH,OH
First Phase of glycolysis ΔG
FirstPhaseofGlycolysisInthefirstphaseofglycolysis,glucose will be phosphorylated at C-1 and C-6.The six-carbon skeleton of glucose will be cleaved toyield two three-carbonmolecules ofglyceraldehyde-3-phosphate.Phosphorylation and cleavage reorganize the glucose molecule andtheATPwillbeused
First Phase of Glycolysis In the first phase of glycolysis, glucose will be phosphorylated at C-1 and C-6. The six-carbon skeleton of glucose will be cleaved to yield two threecarbon molecules of glyceraldehyde-3-phosphate. Phosphorylation and cleavage reorganize the glucose molecule and the ATP will be used
EnergyinvestmentphaseCH,OHCH,OPO?ADPhexokinaseOHOHAOHGlucoseGlucose-6-phosphateStep 1AkinaseaddsphosphateIrreversible1ststep commitsmetabolitetopathway (one-wayarrow)4G2=-16.7kJ/molBlocksglucosefromtransportoutofcellAdds 1 of 2@neededforStep4
Energy investment phase Step 1 A kinase adds phosphate Irreversible 1st step commits metabolite to pathway (one-way arrow) ΔG’ = -16.7 kJ/mol Blocks glucose from transport out of cell Adds 1 of 2 needed for Step4
Step1-phosphorylation ofglucoseGlucose is phosphorylated by hexokinase or glucokinaseThis is a priming reaction.ATPisconsumedhereATP makes the phosphorylation of glucose spontaneousα-D-Glucose +ATP4-→α-D-glucose-6-phosphate2-+ADp3-+H+4G=-16.7kl/mol
Step 1- phosphorylation of glucose Glucose is phosphorylated by hexokinase or glucokinase. This is a priming reaction. ATP is consumed here. ATP makes the phosphorylation of glucose spontaneous