Cellular respiration is a series of metabolic processes wherein the biochemical energy is harvested from organic substance (e.g. glucose) and stored in energy-carriers (e.g. ATP) for use in energy-requiring activities of the cell. The major steps or processes of cellular respiration are (1) glycolysis, (2) Krebs cycle, and (3) oxidative phosphorylation.
Oxidative phosphorylation is an enzymatic process that occurs in both prokaryotes and eukaryotes. In eukaryotes, the process occurs as part of cellular respiration within the mitochondrion. In prokaryotes, it occurs in the cell membrane itself. This process is a more efficient method to produce ATP (in terms of net ATP yield) than fermentation. The process however involves oxidation that it produces reactive oxygen species, which contributes to the propagation of free radicals.
Oxidative phosphorylation is carried out through a series of compounds in a chain called the electron transport chain. In this chain, electron is transferred from one compound to another via redox reactions. It is coupled with the transfer of proton (H+ ion) across the membrane resulting in the creation of a proton gradient, which is essential in the synthesis of energy-storing compounds, e.g. ATP. Thus, the electron transport chain is a crucial cellular machinery for its major role in extracting energy via redox reactions in cellular respiration as well as in photosynthesis. The electron transport chain is comprised chiefly of electron donors and acceptors. The final electron acceptor is an oxygen molecule, which makes it an aerobic process.