Electron Transport Chain / Oxidative Phosphorylation

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Electron Transport Chain / Oxidative Phosphorylation

So far we have in total, from one glucose molecule...

  • 6CO2s
  • 4 ATPs made directly
  • 10 reduced NADs
  • 2 reduced FADs

Now all the hydrogen from the reduced hydrogen carriers enters a chain of reactions, which ultimately yields energy in the form of ATP.


Each hydrogen atom is split into its constituent H+ (hydrogen ion) and electron. The electron is the part that actually gets passed down the chain from carrier to carrier. The H+, however, remains in the mitochondrial matrix.

The electron carriers are at successively lower energy levels hence, as the electron moves on from one carrier to the next some energy is released.

This energy is used to pump H+ from the matrix into the space between the inner and outer mitochondrial membrane. The H+ concentration therefore increases, forming a concentration gradient.

This means that the H+ ions have electrical potential energy. H+ then flows back down the gradient into the matrix through protein channels.

Associated with each channel is an enzyme, ATP synthase. As the H+ ions flow through, their energy is used to make ATP.

This theory about how the ATP is actually made is called the chemiosmotic theory. Oxygen acts as the final electron acceptor in the chain, so the oxygen, electrons and hydrogen ions together form water.


For every reduced NAD feeding hydrogen into the chain, enough energy is released to make 3 ATP molecules.
For every reduced FAD feeding hydrogen into the chain, enough energy is released to make 2 ATP molecules.


ATPs made directly = 4
ATPs made from reduced NAD = 10 x 3
ATPs made from reduced FAD = 2 x 2


Note: 38 ATPs will be made under only the most favourable conditions. Usually, slightly less than this will be made per glucose molecule.

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