1. Oxidative Phosphorylation

2. Learning Outcomes
(i) outline the process of oxidative phosphorylation, with reference to the roles of electron carriers, oxygen and the mitochondrial cristae;
(j) outline the process of chemiosmosis, with reference to the electron transport chain, proton gradients and ATPsynthase (HSW7a).

3. Oxidative Phosphorylation
Reduced coenzymes from the Krebs cycle are now full of potential energy to make ATP through oxidative phosphorylation.
Oxidative phosphorylation occurs on the cristae of the mitochondrion and involves a series of enzyme controlled reactions.

4. The Stages of Oxidative Phosphorylation
There are cytochrome carriers on the cristae of the mitochondria. Reduced NAD and FAD become oxidised (lose their hydrogen atoms) when they come into contact with these carriers.
The hydrogen atoms split up into protons (+) and electrons (-)
Electrons pass along the cytochrome carriers and the energy released is used to pump protons (H+) into the intermembrane space.

5. The Stages of Oxidative Phosphorylation
Protons create and electrochemical gradient as they cannot pass back through the membrane.
Protons which have built up in the intermembrane space can diffuse through specialised protein channels back into the matrix.
These channels contain a structure on the matrix side which consists of the enzyme ATP synthease and is where ADP is phosphorylated to form ATP.

6. The Stages of Oxidative Phosphorylation
As the protons (H+) flow through these channels they “turn” this enzyme and fuel the process of ATP production. The “used” protons then combine with electrons and oxygen atoms to form water.
The electrons (H-) move along the membrane’s carriers until they reach the final carrier molecule, oxygen.
This process is referred to as chemiosmosis