Electron Transport and Oxidative Phosphorylation

Chapter 1 – Electron Transport and Oxidative Phosphorylation

• Oxidative phosphorylation - process in which NADH and QH2 are oxidized and ATP is produced.
• Enzymes are found in inner mitochondrial membrane in eukaryotes.
• In prokaryotes, enzymes are found in cell membrane.
• Process consists of 2 separate, but coupled processes:
1) respiratory electron-transport chain
• Responsible for NADH and QH2 oxidation
• Final e- acceptor is molecular oxygen
• Energy generated from electron transfer is used to pump H+ into intermembrane space from matrix ---> matrix becomes more alkaline and negatively charged.
2) ATP synthesis
• Proton concentration gradients represents stored energy
• When H+ are moved back across inner mitochondrial membrane through ATP synthase ---> ADP is phosphorylated to form ATP


Chemiosmotic Theory of ATP Production

Proposed by Peter Mitchell in 1961 (won Nobel Prize for this work).
Tenet: Proton concentration gradient serves as energy reservoir for ATP synthesis.
Proton concentration gradient also known as proton motive force (PMF).

Components of Electron Transport System

There are 5 protein complexes:
I) NADH-ubiquinone oxidoreductase
II) succinate-ubiquinone oxidoreductase
III) ubiquinol-cytochrome c oxidoreductase
IV) cytochrome c oxidase
V) ATP synthase

• Electrons flow through ETS in direction of increasing reduction potential.
• Two mobile electron carriers also involved: ubiquinone (Q) between complexes I or II and III, and cytochrome c between complexes III and IV.
• Electrons enter ETS 2 at a time from either NADH or succinate.