Enolase catalyzes the conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP). The deltaG’o for this reaction is +1.8 kJ/mol. If [2-PG] = 0.045 mM and [PEP] = 0.034 mM, what is the actual free energy, deltaG?

To calculate the actual free energy change (ΔG) for the conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP), we can use the equation:

ΔG = ΔG° + RT * ln(Q)

Where:
- ΔG is the actual free energy change
- ΔG° is the standard free energy change
- R is the gas constant (8.314 J/(mol·K) or 0.008314 kJ/(mol·K))
- T is the temperature in Kelvin
- Q is the reaction quotient

Given:
- ΔG° = +1.8 kJ/mol (standard free energy change)
- [2-PG] = 0.045 mM (concentration of 2-phosphoglycerate)
- [PEP] = 0.034 mM (concentration of phosphoenolpyruvate)

We need the concentrations in moles per liter (M), so we divide the given concentrations by 1000:

[2-PG] = 0.045 mM = 0.045 / 1000 = 0.000045 M
[PEP] = 0.034 mM = 0.034 / 1000 = 0.000034 M

The reaction quotient (Q) can be calculated using the concentrations of reactants and products:

Q = [PEP] / [2-PG]

Substituting the given concentrations:

Q = 0.000034 M / 0.000045 M = 0.7556

Now we can calculate the actual free energy change (ΔG) using the equation:

ΔG = ΔG° + RT * ln(Q)

Since the temperature (T) is not specified, we'll assume it to be 298 Kelvin (room temperature):

ΔG = 1.8 + (0.008314 * 298) * ln(0.7556)
ΔG = 1.8 + 2.470962 * ln(0.7556)
ΔG ≈ 1.8 - 0.589
ΔG ≈ 1.211 kJ/mol

Therefore, the actual free energy change (ΔG) for this reaction is approximately 1.211 kJ/mol.