QUANTITATIVE Glucose Phosphorylation. The direct phosphorylation of glucose by inorganic phosphate is a thermodynamically unfavorable reaction:
In the cell, glucose phosphorylation is accomplished by coupling the reaction to the hydrolysis of ATP, a highly exergonic reaction:
Typical concentrations of these intermediates in yeast cells are
Assume a temperature of 25°C for all calculations.
- (a) What minimum concentration of glucose would have to be maintained in a yeast cell for direct phosphorylation (Reaction 9-21) to be thermodynamically spontaneous? Is this physiologically reasonable? Explain your reasoning.
- (b) What is the overall equation for the coupled (ATP-driven) phosphorylation of glucose? What is its ΔG°′ value?
- (c) 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?
- (d) By about how many orders of magnitude is the minimum required glucose concentration reduced when the phosphorylation of glucose is coupled to the hydrolysis of ATP?
- (e) Assuming a yeast cell to have a glucose concentration of 5.0 mM, what is ΔG′ for the coupled phosphorylation reaction?
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Becker's World of the Cell (9th Edition)
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- BiochemistryBiochemistryISBN:9781305577206Author:Reginald H. Garrett, Charles M. GrishamPublisher:Cengage Learning