Question

What are the consequences of variations on the main themes (ie less protons pumped, less ATP made) and how are ETS’s, ATP production, PMF, and Redox potentials related?

Answer 1

Oxidative phosphorylation in eukaryotes is an essential mechanism for the production of ATP, which is the biological energy currency of the cell. This oxidative phosphorylation occurs in the mitochondrial inner membrane and is an endothermic process. In order to maintain the spontaneity, this reaction is coupled with an Electron Transport System (ETS), in the inner membrane of mitochondria that creates an electrochemical gradient or a proton motive force (PMF) across the mitochondrial membrane. This PMF is used to drive the synthesis of ATP through F0F1-ATP synthase. The ETS consists of complexes I-IV, that transfer electrons from electron donors to electron acceptors via redox (both reduction and oxidation occurring simultaneously) reactions, and couples this electron transfer with the transfer of protons (H⁺ ions) across a membrane. For electron transport to be possible,  the redox potential of the acceptor must be more positive than the redox potential of the donor. In eukaryotes, NADH is the most important electron donor. The associated electron transport chain is

NADH ? Complex I ? Q ? Complex III ? cytochrome c ? Complex IV ? O₂ where Complexes I, III and IV are proton pumps, while Q and cytochrome c are mobile electron carriers. The electron acceptor is molecular oxygen.

Any variation in the such as less protons pumped will lead to a disturbance in the PMF in the mitochondria which will lead to less ATP production in the cell. Any sort of disturbance or variation in the elctron trnasport chain will lead to it's effect on oxidative phosphorylation. Uncouplers such as UCP1 etc., which bypass the ATP synthase by carrying the protons themselves lead to dissipation of oxidative enrgy as heat and ATP is not produced consequently.