Two independent metabolic pathways (Pathway A and Pathway B) produce the same fatty…

CHEMISTRY · Multi-part · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

Two independent metabolic pathways (Pathway A and Pathway B) produce the same

C_{16}

fatty acid under standard-state conditions. The stoichiometric requirements for adenosine triphosphate are: • Pathway A: requires

7\,\text{mol}

of ATP hydrolyzed to ADP per mole of fatty acid formed. • Pathway B: requires

5\,\text{mol}

of ATP hydrolyzed to AMP per mole of fatty acid formed. The relevant standard free-energy changes are: ATP

\rightarrow

ADP + Pi

\Delta G^\circ = -30.5\,\text{kJ mol}^{-1}

ATP

\rightarrow

AMP + PPi

\Delta G^\circ = -45.6\,\text{kJ mol}^{-1}

A biotechnology company plans to produce

10.0\,\text{mmol}

of the

C_{16}

fatty acid and can choose either pathway. Assume all reactions occur under standard-state conditions and that coupling is

100\%

efficient. (a) Calculate the total

\Delta G^\circ

(in kJ) associated with ATP hydrolysis for producing

10.0\,\text{mmol}

of fatty acid via Pathway A. (b) Calculate the total

\Delta G^\circ

(in kJ) associated with ATP hydrolysis for producing the same amount via Pathway B. (c) Which pathway is energetically more efficient? Justify your answer quantitatively. (d) Suggest one physiological or evolutionary advantage, other than energetic efficiency, that might favor the less efficient pathway in certain organisms.

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