Final answer:
In cellular respiration, electrons from NADH and FADH2 pass through the electron transport chain in a specific order: firstly to complex I and II, then carried by ubiquinone to complex III, transferred to cytochrome c, then to complex IV and finally to oxygen, forming water. These redox reactions create a proton gradient utilized to synthesize ATP via chemiosmosis in the process of oxidative phosphorylation.
Step-by-step explanation:
Order of Electron Acceptance and Role in Proton Gradient Formation
The electron transport system involves a series of redox reactions that transfer electrons through various membrane-bound carriers embedded within the mitochondrial inner membrane. These redox reactions are facilitated through a series of complexes which include NADH dehydrogenase complex, cytochrome b-c1 complex, cytochrome oxidase complex, and several mobile carriers such as ubiquinone and cytochrome c. The sequence in which these components engage in electron transfer includes:
NADH and FADH2 which donate high-energy electrons.
The electrons are transferred to complexes I (NADH dehydrogenase) and II which start the electron transport chain.
Ubiquinone (coenzyme Q) then receives electrons from both complexes and passes them to complex III (cytochrome b-c1 complex).
Cytochrome c, a mobile electron carrier, transfers electrons from complex III to complex IV (cytochrome oxidase complex).
Complex IV transfers the electrons to oxygen, which is the final electron acceptor, resulting in the formation of water.
Each transfer of electrons between carriers is coupled with the translocation of protons (H+) from the mitochondrial matrix to the intermembrane space, creating an electrochemical gradient. The potential energy stored in this gradient drives the synthesis of ATP as protons flow back into the matrix through the enzyme ATP synthase. This is the main concept behind chemiosmosis and oxidative phosphorylation.