Question

Calculate the DG for ATP hydrolysis in a cell in which the [ATP]/[ADP] ratio had climbed to 100:1, while the Pi concentration remained at 10 mM. How does this compare to the ratio of [ATP]/[ADP] when the reaction is at equiLiBrium and the Pi concentration remains at 10 mM? What would be the value for DG when the reactants and products were all at standard conditions (1 M)?

Answer 1

The standard calculated free energy change (ΔG) for ATP hydrolysis is -7.3 kcal/mol (-30.5 kJ/mol), but it is double that under cellular conditions, -14 kcal/mol (-57 kJ/mol). To calculate ΔG for ATP hydrolysis, you need to convert the ATP/ADP ratio to concentrations, then use the equation ΔG = ΔG° + RTln([ADP][P₁]/[ATP]). The value for ΔG under standard conditions is -57 kJ/mol.

Step-by-step explanation:

The standard calculated free energy change (ΔG) for the hydrolysis of one ATP molecule into ADP and P₁ is -7.3 kcal/mol (-30.5 kJ/mol). However, under cellular conditions, the ΔG for ATP hydrolysis in a living cell is almost double the value at standard conditions, -14 kcal/mol (-57 kJ/mol).

In the given scenario, where the [ATP]/[ADP] ratio is 100:1 and the Pi concentration remains at 10 mM, we can calculate the ΔG for ATP hydrolysis. The equation to calculate ΔG is: ΔG = ΔG° + RTln([ADP][P₁]/[ATP]), where ΔG° is the standard calculated ΔG, R is the gas constant, T is the temperature in Kelvin, [ADP] is the concentration of ADP, [P₁] is the concentration of Pi, and [ATP] is the concentration of ATP.

1. Convert the [ATP]/[ADP] ratio to concentrations by assuming a total concentration of 100 mM. So, [ATP] = 99 mM and [ADP] = 1 mM.
2. Calculate the ΔG using the equation: ΔG = -14 kcal/mol + (1.987 cal/mol*K * 310 K) * ln(1 mM * 10 mM / 99 mM).
3. Convert the ΔG to joules by multiplying by 4.18 J/cal.

The ΔG value when the reactants and products are at standard conditions (1 M) is -57 kJ/mol or -57,000 J/mol.