Apentix/AP Biology/Unit 3: Cellular Energetics/Question
AP Biologyhardmcq1 pt

Protons rushing through ATP synthase are not incorporated into the ATP made there. What actually converts their passage into ATP formation?

A.Each proton is welded onto ADP, supplying the mass missing from the finished nucleotide
B.Frictional heating from proton flow melts the catalytic site open wide enough for bulky ATP to escape
C.Proton flow spins the enzyme's membrane ring and stalk, forcing cyclic conformational changes in the head that press ADP and inorganic phosphate together
D.The flowing protons carry electrons that chemically reduce ADP into the higher-energy ATP molecule

Explanation

Core Concept

ATP synthase behaves like a rotary motor. Protons bind the c ring in the membrane, drive its rotation, and turn the attached gamma stalk inside the F1 head. Each increment of turning rotates three beta subunits through open, loose, and tight states, and the tight state mechanically favors condensation of ADP with inorganic phosphate. The protons exit into the matrix unchanged, having paid for torque rather than for atoms.

Correct Answer

CProton flow spins the enzyme's membrane ring and stalk, forcing cyclic conformational changes in the head that press ADP and inorganic phosphate together

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