Oxidative Phosphorylation

Oxidative Phosphorylation

Cells make use of enzymes to oxidize nutrients thereby releasing energy that is used to reform ATP. This metabolic pathway is termed as oxidative phosphorylation. It takes place inside mitochondria in most of the eukaryotes. Oxidative phosphorylation mainly consists two components chemiosmosis and electron transport chain.


Oxidative phosphorylation uses the chemical reactions that release energy to drive a chemical reaction that requires energy. These 2 sets of reactions are coupled. They are interrelated to each other. The electrons that flow through electron transport chain is an exergonic process and the synthesis of ATP is an endergonic process. These two processes are ingrained within a membrane as a result energy will be transmitted from electron transport chain to ATP synthase by the movement of proteins. This process is termed as chemiosmosis.

Exergonic Process is a chemical reaction in which energy is absorbed. There will be a change in free energy and it is always positive. Endergonic Process is a chemical reaction in which there will a positive flow of energy from the system to the surrounding environment. Chemical reactions are also considered exergonic when they are spontaneous.

Electron Transport Chain in Eukaryotes

Most of the biochemical catabolic processes like the citric acid cycle, glycolysis, beta-oxidation, etc produce the coenzyme NADH. It consists of electrons having high transfer potential. These reactions release a huge amount of energy on oxidation. These reactions are also known to be the uncontrollable reactions since the energy within the cells is not released at once. The electrons are separated from the NADH and then passed to the oxygen with series of enzymes releasing a small amount of energy. All these sets of enzymes having complexes 1 through the 4, is known as electron transport chain. This chain can be seen in the inner layer or membrane of the mitochondria. The salts of succinic acid are also oxidized by this electron chain transport system.

In case of eukaryotes, the enzymes make use of energy that has been released in the electron transport system from the oxidation of NADH that pumps protons across the inner membrane of the mitochondria. This results in the generation of electrochemical gradient across the membrane. This can be considered as one of the best examples to understand the concept of oxidative phosphorylation.

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