Question 23.3: The following overall reaction is a good example of the coup...

The following overall reaction is a good example of the coupling of endergonic and exergonic reactions:
UTP + Glucose 1-phosphate + H_2O  \longrightarrow   Glucose-UDP + 2  HOPO_3  ^{2-}
The coupled reactions are
UTP + Glucose 1-phosphate \longrightarrow  \\                   Glucose-UDP + OP_2O_6  ^{4-}         ΔG = 1.1 kcal/mol
OP_2O_6  ^{4-} + H_2O  \longrightarrow   2  HOPO_3  ^{2-}     ΔG = -8.0 kcal/mol
What is the common intermediate in these coupled reactions? What is ΔG for the coupled reactions? Based on these ΔG values, is the change favorable or unfavorable?
ANALYSIS To find the common intermediate, look for a moiety that appears on the left-hand side of one of the equations and on the right-hand side of the other. In this case OP_2O_6  ^{4-} appears in each equation, but on opposite sides. It must be the common intermediate. To determine the ΔG for the coupled reactions, simply add the ΔGs. If the sign of the sum is negative, the reaction is exergonic and favored; if the sign of the sum is positive, the reaction is endergonic and unfavored.