Question

Oxidative Phosphorylation

Consider a reconstituted membrane system that mimics the structure of intact mitochondria in that the matrix and intermembrane space are completely intact. These membranes are formed with only Complex IV and Complex V (ATP synthase) and these components are in their normal orientation within the membrane. Electrons are provided into the system via soluble reduced Cytochrome C and O2 is used as an electron acceptor

a. Would ATP Synthesis Occur? Explain.

b. If only ATP synthase is inhibited, would the spectral data of the cytochomes in this system indicate that they were all reduced, all oxidized, or somewhere in between? Assume the protein pumping is done somehow by Cyt a3 - the last cytochrome in the complex. Explain

Answer 1

Answer 1:

Oxidative phosphorylation is the process of ATP formation resulting from the transfer of electrons from NADH or FADH₂ to O₂ by a series of electron carriers present in the inner mitochondrial membrane. Generation of ATP in mitochondria depends on the transfer of electrons through a set of carrier proteins (Complexes) which result in the release of H⁺ from mitochondrial matrix to inter membrane space. Due to higher H⁺ concentration outside the membrane a gradient is developed called as Proton Motif Force (PMF). These H⁺ comes back tomitochondrial matrix via Complex V (ATP Synthase). This H⁺ flow provide sufficient rotational energy to Complex V. As ATP synthase turns, it catalyses the addition of a phosphate to ADP, capturing energy from the proton gradient as ATP.

Since Complexes I, III, and IV of the electron transport chain are proton pumps, there won’t be sufficient proton motif force for Complex V to produce ATP.

Answer 2:

If only ATP synthase is inhibited the spectral data of Cytochrome would be somewhere in between as the movement of H⁺ will start happening through uncoupling reaction.