How is the electron transport chain regulated?

One main process is the amount and quality of substrate which is able to provide electrons to the ETC. For example, the presence of the electron carriers NADH and FADH2 are regulated by glycolysis and TCA cycle. These processes are dependent on the energy requirements of the cell and the oxidation of nutrients gives electrons to the ETC by means of NADH and FADH2 molecules. The speed of the ETC is also regulated by the levels of ATP and ADP. When the cell requires more energy, meaning there are low levels of ATP and high levels of ADP present, the ETC must function at a higher speed to generate more ATP. In contrast, when the cell requires less energy, meaning there are high levels of ATP and low levels of ADP present, the ETC functions at a slower speed to conserve energy. The ETC is also regulated by the proton gradient between the inner membrane and the mitochondrial matrix. Electron transfer via the ETC is coupled to proton transfer from the matrix. Thus, an increase of the proton gradient causes an unfavorable reaction in ETC function. Through the reduction of the proton gradient, ATP synthase functions as a sufficient activator of the ETC. The presence of oxygen also regulates the ETC, as it is the final electron acceptor and allows for oxidative phosphorylation. Without oxygen, the electron transport chain will stop functioning and ATP will no longer be generated through chemiosmosis.