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), you need to use the relationship between ΔG and ΔG'0, as well as the concentrations of the reactants and products.
The relationship between ΔG and ΔG'0 is given by the equation:
ΔG = ΔG'0 + RT * ln(Q)
where:
- ΔG is the actual free energy change.
- ΔG'0 is the standard free energy change.
- R is the gas constant (8.314 J/mol·K).
- T is the temperature in Kelvin.
- Q is the reaction quotient, which is the ratio of product concentrations to reactant concentrations.
First, convert the given temperatures to Kelvin, if necessary. Then, calculate the reaction quotient, Q, by taking the ratio of the product concentration ([PEP]) to the reactant concentration ([2-PG]):
Q = [PEP] / [2-PG]
Next, use the equation above to calculate the ΔG:
ΔG = ΔG'0 + RT * ln(Q)
Plug in the given values:
- ΔG'0 = +1.8 kJ/mol (Note: Convert this to J/mol by multiplying by 1000)
- R = 8.314 J/mol·K
- T = temperature in Kelvin (you didn't provide this information, assume a value, e.g., 298 K)
- Q = [PEP] / [2-PG]
Calculate the ln(Q) term by taking the natural logarithm (ln) of Q.
Finally, substitute the values into the equation to calculate ΔG. Remember to convert the units to kJ/mol, if desired.
Let's say the temperature is 298 K (room temperature). Here is how you can complete the calculations step by step:
1. Convert ΔG'0 from kJ/mol to J/mol:
ΔG'0 = 1.8 kJ/mol * 1000 = 1800 J/mol
2. Calculate Q:
Q = [PEP] / [2-PG] = 0.034 mM / 0.045 mM = 0.756
3. Calculate ln(Q):
ln(Q) = ln(0.756) ≈ -0.278
4. Substitute the values into the equation and calculate ΔG:
ΔG = ΔG'0 + RT * ln(Q)
ΔG = 1800 J/mol + (8.314 J/mol·K * 298 K) * -0.278
ΔG ≈ 1800 - 6272 ≈ -4472 J/mol
ΔG ≈ -4.472 kJ/mol
Therefore, the calculated actual free energy change (ΔG) for the conversion of 2-phosphoglycerate to phosphoenolpyruvate is approximately -4.472 kJ/mol.