Question

Please help answer the following questions in detail. Please do not answer if you are not sure. I will give a thumbs up to the correct, detailed answer.

Question 39

Peter Mitchell developed the Chemiosmotic Theory (also known as the proton motive force) in the 1960's. Two key observations were critical in the development of this theory.

Part 39A

Mitchell noted that the pH of the intermembrane space is lower than the pH of the mitochondrial matrix. How is this achieved?

Part 39B

In a laboratory preparation of mitochondria, Mitchell observed that oxidative phosphorylation does not occur in the presence of detergents that were used to extract mitochondria from cells. He concluded that these detergents disrupted the inner mitochondrial membrane. Briefly explain why oxidative phosphorylation cannot occur under these conditions.

Answer 1

Peter Mitchell proposed the chemiosmotic theory to explain ATP formation.
According to this theory, ATP formation requires the development of proton gradient across a biological membrane. The following components are required for that process.
1. A membrane
2. Electron/proton carriers
3. Electron/proton donors
4. Electron/proton acceptors
5. ATP synthase complex

A. During oxidative phosphorylation,
1. A membrane = Inner mitochondrial membrane
2. Electron/proton carriers = Complexes I, II, III, and IV
3. Electron/proton donors = NADH and FADH2
4. Electron/proton acceptors = Molecular oxygen
5. ATP synthase complex

NADH/FADH2 donate electrons to the electron carriers which pump protons from the mitochondrial matrix to the perimitochondrial space. This leads to high H+ ion concentration in the perimitochondrial space i.e. low pH.

B. The membrane used for electron transport must be impermeable to the movement protons such that protons are pushed through ATP synthase for ATP production.
The use of a detergent destabilizes the membrane integrity and protons can easily diffuse through leading to the dissipation of proton gradient. Hence, ATP synthesis cannot occur.