- Oxidation describes the loss of an electron by a molecule, atom or ion
- Reduction describes the gain of an electron by a molecule, atom or ion
Stage III - The Electron Transport Chain
During this series of reactions, each of the reduced coenzymes (NADH and FADH2) contributes a pair of electrons to a series of electron accepting compounds located on the inner membrane of the mitochondria. NADH passes its electrons to three acceptor molecules in succession. FADH2 only passes electrons to two acceptors.
2H 2H+ + 2e
Each time the pair of electrons from NADH
are released by an electron acceptor, energy
is given off. This energy is trapped
in a molecule of ATP. Since NADH
passes electrons to three acceptors, 3 ATP
are produced for each reduced NADH molecule.
For each reduced FADH2 molecule produced in the Krebs cycle, two ATP are produced. The ten NADH molecules produced during glycolysis and the Krebs cycle give rise to 30 ATP in the electron transport chain. The two FADH2 molecules give rise to 4 ATP.
The net gain of ATP from the breakdown of glucose is:
Final Net: 4 ATP (direct)
30 ATP (from NADH)
+ 4ATP (from FADH2)
38 ATP (minus 2 ATP) = 36 ATP net
After being released by the last electron acceptor, the pair of electrons are accepted by oxygen atoms. These atoms become charged (O2-). The charged oxygen ions combine with the remaining hydrogen ions to form water. The purpose of oxygen in the breakdown of glucose is to serve as the final acceptor of the electrons.