The free energy change (G) for an enzymatic reaction under cellular conditions m

Question

The free energy change (G) for an enzymatic reaction under cellular conditions must be negative for a reaction to occur in the direction as written. Thus, the concentrations of metabolites in cells need to be in favor of producing a negative G for a given enzymatic reaction. Answer the following questions for the reaction shown below.

acetyl CoA + H2O <==> CoASH + acetic acid   G°'= -32.0 kJ/mol

A) Calculate the free energy change at 25°C at pH 7.0 in a cell where the concentration of acetyl CoA, CoASH, and acetic acid are 1.2 mM, 85µM, and 15µM respectively. (Note: under standard conditions, [H2O]= 1.0M).

B) Is the reaction more favored under the given cellular conditions or at equilibrium conditions? Why or why not?

C) Based on your calculations can millimolar concentrations of acetyl CoA exist in a cell? Why or why not?

Explanation / Answer

(A): The given reaction is

acetyl CoA + H2O <==> CoASH + acetic acid   G°'= -32.0 kJ/mol

Now we need to find the Gibbs free energy for the following cncentration.

[acetyl CoA] = 1.2 mM = 1.2x10-3 M

[CoASH] = 85 microM = 85x10-6 M

[Acetic acid] = 15x10-6 M

Now the reaction quotient 'Q' for the above concentration can be calculated as

Q = [CoASH] x [Acetic acid] / [acetyl CoA] = (85x10-6 M x15x10-6 M) / 1.2x10-3 M

Now the Gibbs's free energy change can be calculated from the following formulae.

DeltaG = DeltaG0 + RTxlnQ

=> DeltaG = - 32.0 KJ/mol + 8.314JK-1mol-1x 298Kx ln [(85x10-6 M x15x10-6 M) / 1.2x10-3 M]

=> DeltaG = - 32.0 KJ/mol - 34079 J/mol =  - 32.0 KJ/mol - 34.079 KJ/mol = - 66.079 KJ/mol

(B) Since the negative value of DeltaG increased further, the reaction is more favored under the given cellular condition.

(C) Since the reaction is even more favorable when the concentration of acetyl CoA is in millimolar, hence millimolar concentrations of acetyl CoA can exist in a cell.

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.