Biology Forums - Study Force

In the photosynthetic archaean Halobacterium halobium, a membrane transport protein called bacteriorhodopsin captures energy from sunlight and uses it to pump protons out of the cell.
 
  The resulting proton gradient serves as an energy store that can later be tapped to generate ATP. Which statement best describes how bacteriorhodopsin operates?
  (a) The absorption of sunlight triggers a contraction of the  barrel that acts as the protein's central channel, squeezing a proton out of the cell.
  (b) The absorption of sunlight triggers a shift in the conformation of the protein's seven, membrane spanning  helices, allowing a proton to leave the cell.
  (c) The absorption of sunlight triggers a restructuring of bacteriorhodopsin's otherwise unstructured core to form the channel through which a proton can exit the cell.
  (d) The absorption of sunlight triggers the activation of an enzyme that generates ATP.

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