Chemistry

Problem

Carboxylation of pyruvate to oxaloacetate is endergonic with

\Delta G^{\circ}=+32\,\text{kJ}\,\text{mol}^{-1}

and proceeds in cells by coupling to the hydrolysis of one ATP per reaction. If a cell has

5.0\,\text{mmol}

of ATP available, what is the maximum amount of oxaloacetate (in mmol) that can be produced under standard conditions? a)

4.8

5.0

2.5

7.9

Intuitive explanation

This problem is about thermodynamic coupling—using a favorable reaction (ATP hydrolysis) to drive an unfavorable one. The key insight is that ATP hydrolysis releases enough free energy to overcome the positive $\Delta G°$ of carboxylation, but only if you have enough ATP molecules. Calculate the total free energy available from your ATP supply, compare it to the energy cost per oxaloacetate molecule, and that ratio tells you the maximum yield.

Intuitive explanation

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