Chemiosmosis and ATP synthase Transitional Reasoning Practice

Questions

1. 1.

   Researchers prepared artificial membrane vesicles containing functional ATP synthase complexes oriented with their catalytic $F_1$ subunits exposed to the surrounding buffer. The vesicles, initially equilibrated at pH 4.0, were rapidly transferred to an incubation medium maintained at pH 8.0 containing ADP and inorganic phosphate ($P_i$) in the absence of any electron transport chain proteins. Under these conditions, the vesicles synthesized ATP until the pH across the bilayer equalized. Which statement is best supported by this experimental observation?

   • A) Electron transport chain complexes must physically interact with ATP synthase to catalyze ADP phosphorylation.
   • B) ATP synthase hydrolyzes high-energy intermediates to actively pump protons across the artificial lipid bilayer.
   • C) The electrochemical proton gradient alone provides sufficient proton-motive force to power ATP synthesis through ATP synthase.
   • D) Protons must move against their concentration gradient into the vesicles to trigger catalytic conformational changes.

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