Step1-phosphorylation ofglucoseHexokinase(andglucokinase)acttophosphorylate glucose and keep it in the cellExtracellularCytoplasmfluidGlucosGlucose Hexokinase (K.glucose = 0.1 mM)nCell has 4 mm glucoseADPSo hexokinase is normally active!Glucose-Glucoseiskeptinthecellby phosphorylationto G6P,6-phosphatewhich cannot easily crosstheplasmamembrane Glucokinase (K.glucose = 10 mM) only turns onwhen cell is rich inglucose!
Step 1- phosphorylation of glucose Hexokinase (and glucokinase) act to phosphorylate glucose and keep it in the cell Hexokinase (Km glucose = 0.1 mM) Cell has 4 mm glucose So hexokinase is normally active! Glucokinase (Km glucose = 10 mM) only turns on when cell is rich in glucose!
G-6-P is the branch point for several metabolic pathwaysGlucoseEnergystorageinGlycogenliverandmusclesPentoseGlucose-6-phosphateGlucose-l-phosphatephosphate[glu'kjuraneit]pathwayGlucuronateCarbohydratesynthesis葡糖醛酸盐Fructose-6-phosphate-→Glucosamine-Synthesis of6-phosphateNADPHand4-C,5-C,and7-CsugarsGlycolysis continues
G-6-P is the branch point for several metabolic pathways. 葡糖醛酸盐 [ɡlu'kjurəneit]
Energyinvestmentphase2O,POCH20,POCHCH,OHOHphosphoglucoseHOOHIsomeraseHOOHGlucose-6-phosphateFructose-6-phosphateStep2:isomerizationtofructose4G02=+2.2kJ/mol4G=-1.4kJ/molDuetoreactantconcentrationsFreelyreversible(two-wayarrow
Step 2: isomerization to fructose ΔG0’ = + 2.2 kJ/mol ΔG = - 1.4 kJ/mol Due to reactant concentrations Freely reversible (two-way arrow) Energy investment phase
Step2:Glucose-6-PtoFructose-6-P['ka:banil]炭基的The carbonyl oxygen of glucose-6-phosphate is shiftedfrom C-1 to C-2.6-phosphate (G6P)Theenzymeresponsibleforthisisomerizationis-0-1ophosphoglucoisomerase,alsoknown asphosphoglucoseisomeraseandglucosephosphateisomerase.CHOHThevalueofG undercellularconditions is-2.92kJ/mol.ei(FEPThissmall value meansthatthereactionoperatesnear-POFequilibrium in thecell and is readily reversible
Step 2: Glucose-6-P to Fructose-6-P The carbonyl oxygen of glucose-6-phosphate is shifted from C-1 to C-2. The enzyme responsible for this isomerization is phosphoglucoisomerase, also known as phosphoglucose isomerase and glucose phosphate isomerase. The value of ΔG under cellular conditions is -2.92 kJ/mol. This small value means that the reaction operates near equilibrium in the cell and is readily reversible. [ˈkɑːbəˌnɪl] 羰基的
Energyinvestmentphase20,POCHCH,OPO2O,POCCH,OHADPATPphosphofructokinaseOHHOHOFructose-6-phosphateFructose-1,6-bisphosphateStep3:adde4Go=-17.2kJ/mol (irreversiblestep,one-wayarrow)Thisistheflux-controlpoint orratedeterminingreactionEnergy supplied by destabilizes the molecule-more apt to splitMust convert to ketose before 2nd @ added - or ring unable to open
Step3：add ΔG0’ = -17.2 kJ/mol (irreversible step, one-way arrow) This is the flux-control point or rate determining reaction. Energy supplied by destabilizes the molecule – more apt to split Must convert to ketose before 2nd added – or ring unable to open. Energy investment phase