You have reconstituted into the same membrane vesicles purified bacteriorhodopsi

Question

You have reconstituted into the same membrane vesicles purified bacteriorhodopsin, which is a light-drive H+ pump from a photosynthetic bacterium, and purified ATP synthase from ox heart mitochondria. Assume that all molecules of bacteriorhodopsin and ATP synthase are oriented as shown in the figure below, so that protons are pumped into the vesicle and ATP synthesis occurs on the outer surface.

a. If you add ADP and phosphate to the external medium and shine light into the suspension of vesicles, would you expect ATP to be synthesized? Why?

b. If you prepared the vesicles without being careful to remove all the detergent, which makes the bilayer leaky to protons, would you expect ATP to be synthesized? Why?

c. You tell a friend over dinner about your new experiments. He questions the validity of the approach that utilizes components from so widely divergent, unrelated organisms. As he puts it, “Why would anybody want to mix vanilla pudding with brake fluid?” Defend your approach against his criticism.

Explanation / Answer

a. Membrane proteins function as large complexes. They can function in isolation if they are given the right conditions. So in this case ATP would be synthesized as the right conditions are present for proton pumping and production of ATP by ATP synthase.

b. If the bilayer is leaky to protons, no ATP would be synthesized. This would happen because the leaky bilayer would fail to establish a proton gradient across the plasma membrane which is a prerequisite for ATP synthesis by ATP synthase enzyme.

c. The organisms may be widely divergent but the function of such crucial protein complexes are evolutionarily conserved and serves as a good example that life diverged from single form. Hence the experiment is totally valid and is a good funcitonal example of unrelated protein complexes.

"A malaria biologist"

Related Questions

Navigate

• Browse (All)
• Browse Y
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.