10 May 2010 Lecturer: Dr BS Wilhelmi

Electron transport and oxidative phosphorylation

Electrons released during glucose oxidation are transferred to the co-

enzymes NAD+ and FAD to form 10 NADH and 2 FADH2, in the reactions

catalyzed by glyceraldehydes-3-phosphate dehydrogenase, pyruvate

dehydrogenase, isocitrate dehydrogenase, α-ketoglutarate

dehydrogenase, succinate dehydrogenase and malate dehydrogenase.

The electrons then pass to the mitochondrial electron-transport chain,

where they participate in the sequential oxidation-reduction of over 10

redox centers in 4 enzymes complexes, before reducing O2 to H2O.

During the electron transfer, electrons are expelled into the inter-

membrane space of the mitochondria, producing a proton gradient. The

free energy from the electrochemical gradient drives the synthesis of

ATP from ADP and Pi through oxidative phosphorylation.

References

Voet and Voet, Chapter 22, p 563

Garrett and Grisham, Chapter 21, p 673

Self assessment

1. Outline the movement of electrons from NADH to O2.

2. Summarize the chemiosmotic theory and give key experimental

observations that support this theory.

3. Describe the binding change mechanism of F1F0-ATP synthase.

4. Briefly explain (using a diagram) how protons are shuttled to the

intermembrane space in complex III (Cycle Q).

5. a. How many ADPs are phosphorylated from the transfer of

electrons from 1 mol NADH?

b. How many ADPs are phosphorylated from the transfer of

electrons from 1 mol FADH2?

c. Why does the production of ATP differ, depending on the

initial electron donor?