Consider the remarkable structure of the F1Fo ATP synthase shown in the following schematic drawing. Answer the following question(s) based on the structure.

-As seen from the F? head in the matrix, the rotation of the c ring is counterclockwise in the ATP-synthesis mode of the motor and clockwise in the ATP-hydrolysis mode of the motor. As shown in the above drawing, the "a subunit" (labeled 2) is part of the stator embedded in the membrane, and it forms the entry and exit sites for the protons that are bound by the rotating c ring. How do you think the two half-channels of the a subunit are arranged as seen from the c ring? Write down A or B from the following schematic diagram as your answer.

Question

Consider the remarkable structure of the F1Fo ATP synthase shown in the following schematic drawing. Answer the following question(s) based on the structure.
 
-As seen from the F? head in the matrix, the rotation of the c ring is counterclockwise in the ATP-synthesis mode of the motor and clockwise in the ATP-hydrolysis mode of the motor. As shown in the above drawing, the "a subunit" (labeled 2) is part of the stator embedded in the membrane, and it forms the entry and exit sites for the protons that are bound by the rotating c ring. How do you think the two half-channels of the a subunit are arranged as seen from the c ring? Write down A or B from the following schematic diagram as your answer.

Quizplus · Accepted Answer

In the ATP-synthesis mode, protons move from the cristae space into the matrix (downward in the diagram), which rotates the c ring counterclockwise as seen from the F₁ head on the matrix side of the crista membrane. Thus, in part B of the diagram shown, protons will enter the right half-channel, bind to a c subunit, rotate along with the c ring, and only be able to exit from the left half-channel after a complete turn of the ring. If the channels were arranged as in part A, the protons could pass through the membrane after only a tiny rotation of the ring, so that many more protons would need to pass through the ATP synthase for every ATP molecule that is synthesized by the F? head.

Consider the Remarkable Structure of the F1Fo ATP Synthase Shown