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Electron transport chain (ETC)

by Ramneet Kaur

Electron Transport Chain

Electrons from NADH and FADH2 are passed through a series of electron acceptors present in the inner membrane of mitochondria.

  • 2 NADH produced during glycolysis,
  • 2 NADH, produced during pyruvic acid oxidation, &
  • 6 NADH AND 2 FADH2, produced during Kreb cycle.

Four enzyme complexes of ETC

  1. Complex I – NADH dehydrogenase complex.
  2. Complex II – Succinate-UQ reductase complex.
  3. Complex III – UQH2-cytochrome c reductase complex.
  4. Complex IV – Cytochrome c oxidase complex.


  • When NADH is passed through ETC, complex I, III and IV are involved & 6 pairs of H+ are pushed into the intermembrane space.
  • When FADH2 is passed through ETC, complex II, III and IV are involved & 2 pairs of H+ are pushed into the intermembrane space.


 F0– F1 particles/ ATPase complex (Chemiosmotic Hypothesis)

  • The inner membrane is impermeable to H+ .
  • So, they return back with the help of F0– F1 particles/ ATPase complex present in the inner membrane.df682d9ac30951518997f3a85cb7a660
  • 1 ATP is synthesized by the ATPase complex for every 2 H+ passing through the proton tunnel.
  • As oxidation of NADH/ FADH is responsible for the formation of ATP it is also referred as oxidative phosphorylation.







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