Part 1 The G°’ for the fumarase reaction is -0.81 kcal/mol, but the actual G val

Question

Part 1

The G°’ for the fumarase reaction is -0.81 kcal/mol, but the actual G value in cells is close to zero. What is the approximate ratio of malate to fumarate under cellular conditions at 37 °C. Report your answer to the nearest tenth.

Part 2

Consider the information presented in the previous question that discussed fumarase (i.e., G°’ = -0.81 kcal/mol; G = 0). Given those conditions, what fraction (expressed as a percentage to the nearest ones) of the molecules are fumarate molecules under cellular conditions? (Thought question given your answer to this and the previous question: is the fumarase reaction likely to be a point of regulation in the TCA cycle?)

Explanation / Answer

malate < => fumarate

The relation between G°, G and C product and C reactant as follows:

G = G0 + RT ln C product /C reactant

Here G = 0 but G0= -0.81 kcal/mol or - 3389.04 J / mol nad T = 37 °C = 310K

0 = - 3389.04 J / mol + 8.314 JK1mol1 *310 ln C product /C reactant

3389.04 J / mol   / 2577.495J / mol = ln C fumarate /C malate

ln C fumarate /C malate= 1.315

C fumarate /C malate= 3.7

the approximate ratio of malate to fumarate under cellular conditions at 37 °C is 3.7

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