Hydrolysis of ATP to ADP and Pi
1. The relationship of free-energy change to the concentrations of reactants and products is important be-
cause it predicts the direction of spontaneous chemical reactions. Consider, for example, the hydrolysis
of ATP to ADP and Pi:
ATP + H20 yields ADP + Pi
The free-energy change due to ATP hydrolysis is:
deltaG = deltaG standard + RT ln [ADP][Pi]/[ATP]
where the concentrations are expressed as molarities. Here,delta G = -7.3 kilocalories/mole
(a) Calculate deltaG for ATP hydrolysis when the concentrations of ATP, ADP and Pi are all equal to 1M. What is delta G when the same concentrations are equal to 1mM?
(b) What will delta G equal when the hydrolysis reaction reaches equilibrium? At [Pi] = 10mM, what will be the ratio of [ATP] to [ADP] at equilibrium?
(c) Show that, at constant [Pi],delta G decreases by 1.4 kcal/mole for every 10-fold increase in the ratio of [ATP] to [ADP],independent of delta G.Add to favorites