Explain how the free energy of oxidation of NADH and FADH2 i

Explain how the free energy of oxidation of NADH and FADH2 is used to synthesize ATP

Solution

The NADH molecules produces during glycolysis and TCA cycle are re-oxidised during electron transport chain (ETC). During electron transfer, the free energy produced is used by complex I, III and IV are used to pump protons (H+) across the inner membrane to the intermembrane space. These three complexes are proton pumps, which derive the free energy of electron transfers and carry out active transport of protons against the concentration gradient. This causes an electrochemical gradient across the inner membrane.

This gradient is electrochemical. This is electrical because, pumping of protons causes a difference of voltage across the membrane, much the same as nerve conduction. The chemical nature of the gradient results from the concentration gradient due to the active transport of protons (H+ ions).

This electrochemical gradient is used by the ATP-synthase, to allow H+ ions back into the matrix. This time, the movement of the proton is downhill, down the electrochemical gradient, which produces free energy, so that ATP molecule is synthesized.