Given the information above complete the following questions: 1. What minimum co

Question

Given the information above complete the following questions:

1. What minimum concentration of glucose would have to be maintained in a yeast cell for the coupled reaction to be thermodynamically spontaneous? Is this physiologically reasonable?

2. Assuming ESL to have a glucose concentration of 5.0 mM, what is the deltaG' for the coupled phosphorylation reaction?

he direct phosphorylation of glucose by P, is a thermodynamically unfavorable reaction. In the cell, glucose phosphorylation is accomplished by coupling ther 2. T Rxn #1 glucose + Pi-) glucose-6-P + H2O G": +3.3 kcal/mol Rxn #2 ATP + H2O-) ADP + Pi G", #-7.3 kcal/mol Typical concentrations of the intermediates in yeast cells at 25°C are [glucose-6-P] 0.07 mM [ATP] : 1.9 mM [ADP] 0.13 mM [P] 1.1 mM

Explanation / Answer

1. ?G'=?Go' + RT ln [(Glucose-6-phosphate)(ADP) / (glucose)(ATP)

= -4000+(1.987)(298) ln [(.07x10-3)(.13 x10-3)/(glucose)(1.9x10-3)]

=-4000+592 ln (6.67x10-6)/glucose

= -4000 + 592 ln (6.67x10-6) - 592 ln glucose

= -4000 - 7055 - 592 ln glucose= 11055- 592 ln glucose

At equlibrium ?G' = 7.76 x 10-9 M, this means that glucose concentration of 7.76 x 10-9 M would bring the reaction to equilibrium. Any glucose concentration higher that will render the reaction spontaneous in the direction phosphorylation. This is physiologically very reasonable because glucose phosphorylation is thermodynamically feasible as long as the glucose concentration remains more than 0.01uM.

2. ?G'=?Go' + RT ln [(Glucose-6-phosphate)(ADP) / (glucose)(ATP)

= -4000+(1.987)(298) ln [(5x10-3)(.13 x10-3)/(glucose)(1.9x10-3)]

=-4000+592 ln (0.34 x 10-3)/glucose

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