BIOCHEMISTRY - Textbook - Ostapchenko L. I. - 2012

Chapter 16. ENERGY METABOLISM

16.2. Oxidative Phosphorylation of ADP

Electrons always tend to move from electronegative to electropositive systems; therefore, their transport along the Electron Transport Chain (ETC) to oxygen is accompanied by a decrease in Free energy.

A comparison of the electrochemical potentials of electron carriers (see Table 16.2) shows that the decrease in free energy occurs at each step of the ETC, meaning electron energy is released in discrete portions.

At the same time, three segments can be distinguished in the Respiratory Chain where electron transfer is accompanied by a relatively large decrease in free energy. These stages are capable of providing energy for ATP synthesis, as The amount of released free energy is approximately equal to the energy required to synthesize ATP from ADP and P_i. It has been experimentally confirmed that The process of Electron transport along the ETC and ATP synthesis are energetically coupled.

The first process—The transfer of electrons from the reduced Coenzymes NADH and FADH₂ through the ETC to oxygen—is exergonic. For example:

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The second process—the phosphorylation of ADP, or ATP synthesis—is endergonic:

The synthesis of ATP from ADP and H₃PO₄ driven by the energy of electron transport along the ETC is called Oxidative Phosphorylation.