Given the table of values for the hydrolysis of some phosphorylated compounds, which of the following best describes the DG0′ for the following reaction? phosphoenolpyruvate + ADP → pyruvate + ATP

A) −22.1 kcal/mol
B) −14.8 kcal/mol
C) −7.8 kcal/mol
D) −7.0 kcal/mol
E) −5.0 kcal/mol

Question

Given the table of values for the hydrolysis of some phosphorylated compounds, which of the following best describes the DG0′ for the following reaction? phosphoenolpyruvate + ADP → pyruvate + ATP

A) −22.1 kcal/mol 
B) −14.8 kcal/mol 
C) −7.8 kcal/mol 
D) −7.0 kcal/mol 
E) −5.0 kcal/mol

Quizplus · Accepted Answer

When 2 reactions are coupled, the resultant free-energy change is the arithmetic sum of the ΔG^0' values for the coupled reactions. In the case of the coupled reaction, ATP is not being hydrolyzed but instead is being formed. In this case the ΔG^0' value for a given reaction is its reciprocal value when the reaction is running in the opposite direction to that for which the ΔG^0' value is denoted. Thus, for ATP synthesis from ADP, the ΔG^0' value would be +7.0kcal/mol. When the 2 reactions are coupled, there is sufficient energy released from the hydrolysis of phosphoenolpyruvate to drive the synthesis of ATP from ADP. The ΔG^0' value for the coupled reactions is the simple arithmetic sum of the ΔG^0' values for the individual reactions.

Given the Table of Values for the Hydrolysis of Some