The synthesis of ATP molecule in the presence of oxygen is called oxidative phosphorylation. Oxidative phosphorylation takes place during respiratory chain. Three ATP molecules are formed during three steps of the respiratory chain. This process can be expressed by following equation:

NADH +H+ + 3ADP + 3Pi + 1/202 –>NAD+ + 4H20 + 3ATP

The Pi is an inorganic phosphate. The molecular mechanism of the oxidative phosphorylation is associated with the respiratory chain. These respiratory chains are present in she inner membrane of mitochondria. The mechanism of oxidative phosphorylation is chemiosmosis.

The coupling reaction in which synthesis of ATP molecule takes during movement of 1-1* across an H+ gradient is called chemiosmosis. It is a process that uses membranes during redox reaction for ATP production.

  1. The electron transport chain (ETC) pumps the protons (IT ) across the inner membrane of mitochondria. The movement of electron provides energy for the pumping of electron through the ETC. This energy is transferred into potential energy. The potential energy. is stored in the form of H• gradient across the membrane. It is called electro motive forces.
  2. The inner membrane of the mitochondria is folded into cristae. These cristae have Fl particles. The protons (IF ) are pumped from matrix into intermembrane space through this inner membrane. They come back from the intermembrane space into matrix and pass through the Fl particles.
  3. The F1 particles contain an ATP synthase enzyme. So it uses the energy of proton to synthesize the molecules of ATP.


The eukaryotic cell obtains a net gain of 36 AT} ) molecules from the breakdown of each glucose molecule.



I. Glycolysis: Glycolysis produces four ATP molecules. But two are used in the glycolytic reactions. The two molecules of NADU formed during glycolysis produce six ATP molecules. But two are used in the reactions that transport the N.ADH electrons across the inner mitochondria! membrane into the matrix.

  1. Formation of acetyl COA: One molecule of NADH is produced for each pyruvate converted into acetyl-coenzyme A. One molecule of CO, is released as acetyl coenzyme A enters into the Krebs cycle.
  2. Krebs cycle: Two more ATP molecules are produced in the Krebs cycle. Similarly. six NADH and two FADH, molecules are produced . during Krebs cycle.
  3. Electron Transport Chain: The six NADH from the Krebs cycle and two NADH from the entry of acetyl-coenzyme A into the electron transport chain. They yield 24 ATP molecules. The oxidation of the two molecules of FADIE produced four more molecules of ATP. The net gain from all of these reactions is 36 molecules of ATP.

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