ATP yield and efficiency Transitional Reasoning Download PDF

Questions

1. 1.

   A researcher determines that the complete aerobic respiration of one mole of glucose ($\Delta G^\circ = -686\text{ kcal/mol}$) yields an average of 32 moles of ATP in isolated animal cells. Under standard conditions, the hydrolysis of one mole of ATP to ADP and inorganic phosphate yields $7.3\text{ kcal/mol}$. When a chemical uncoupler of oxidative phosphorylation is added to the cell suspension, oxygen consumption continues at a high rate, but ATP yield declines sharply. Based on thermodynamic principles and respiration mechanisms, which statement accurately evaluates this cellular system?

   • A) The standard thermodynamic efficiency drops from roughly 68% to zero because the uncoupler completely halts both oxidative and substrate-level phosphorylation.
   • B) The basal energy conversion efficiency exceeds 50%, and uncoupling eliminates oxygen consumption by permanently inhibiting Complex IV of the electron transport chain.
   • C) The energetic efficiency of the cell increases during uncoupling because the excess thermal energy released is directly converted into usable chemical work.
   • D) The standard energy conversion efficiency is approximately 34% under basal conditions, and uncoupling causes the proton motive force to dissipate primarily as thermal energy instead of synthesizing ATP.