Question

Calculate the physiological free energy, ∆G, for the reaction: phosphocreatine + ADP → creatine + ATP.

a) Depends on temperature
b) -7.7 kJ/mol
c) +7.7 kJ/mol
d) 0 kJ/mol

Answer 1

The correct answer is 'b) -7.7 kJ/mol' for the ΔG of the reaction phosphocreatine + ADP → creatine + ATP, as this describes an exergonic reaction that releases energy.

Step-by-step explanation:

To calculate the physiological free energy, ΔG, for the reaction: phosphocreatine + ADP → creatine + ATP, we can consider information regarding ATP hydrolysis. ATP hydrolysis is an exergonic reaction that normally releases about -7.3 kcal/mol (-30.5 kJ/mol) of energy under standard conditions. However, the ΔG for ATP hydrolysis inside a living cell is higher, around double the standard condition value, equating to -14 kcal/mol (-57 kJ/mol). Applying this understanding to the phosphocreatine + ADP → creatine + ATP reaction, which involves the conversion of phosphocreatine to ATP, we can infer that this reaction is also exergonic, and therefore the ΔG would be negative.

The reaction is spontaneous, which implies that energy is released, so the correct answer is 'b) -7.7 kJ/mol'. Note that ΔG can indeed depend on temperature and conditions within the cell, but with the giving values -7.7 kJ/mol is a likely approximation under physiological conditions.