1. Mitochondrial Electron Transfer
Electron transport in mitochondria.

2. The Big Picture (One last time)
The major paths that produce NADH and FADH2. The electrons are transferred to oxygen.

3. Mitochondria
Electron transport occurs in the mitochondria - an organelle. Enzymes are located in particular substructures of the mitochondria as listed.

4. Evolutionary Origin of Mitochondria
Mitochondria presumably came from bacteria.

5. Mitochondrial Electron Carriers
NADH and FADH2 (Flavoproteins)
Dehydrogenases
Iron-sulfur proteins
Cytochromes
Ubiquinone (Coenzyme QCoQ)
In inner mitochondrial membrane
Highly-organized complexes
Important points about mitochondria.

6. Iron-Sulfur Proteins (Fe-S)
The proteins of the complex contain functional iron-sulfur proteins that undergo oxidation and reduction.

7. Cytochromes
Heme in Cytochrome c
Cytochromes carry electrons.

8. Mitochondrial Cytochromes
One electron carriers
Fe+3 + e–  Fe2+
Eo depends on
associated proteins
There are cytochromes with different structures and different redox potentials.

9. Ubiquinone  UQ  CoQ
A lipid soluble carrier moves freely in the lipid membrane.

10. Order of Mitochondrial e– Carriers
Detection of oxidized, reduced forms
Visible spectra ( nm)
epr spectra (Fe-S proteins)
Order by Eo
Kinetics of oxidation
Effects of specific inhibitors
Biochemical dissection of complexes
How do you determine the order of functioning of the carriers?

11. Carrier Order by Oxidation Kinetics
1. Mitos with
NADH, no O2:
all reduced
2. At time zero,
add O2
Order of reduction.

12. Carrier Order by Inhibition
Specific inhibitors act at specific sites.
Carriers ahead of block are reduced
Carriers behind block are oxidized

13. Carrier Order by Dissection
Take the mitochondria apart need detergent.
Karp, Gerald. Cell and Molecular Biology, 2e

14. Electron-Transfer Complexes: H+ Pumps
A picture of the organization
As electrons flow to O2, H+ flows out

15. Complex III
A protein from complex III.

16. Complex IV
One from complex IV.

17. Cu Center of Complex IV
The Cu center in complex IV.

18. Respiration in Mitochondria
3 reactions
Substrate is oxidized
O2 consumed (H2O)
ADP + Pi  ATP
Oxidation, oxygen consumption, and ATP formed in parallel.

19. Oxidation and Phosphorylation
Coupled processes
Block electron flow (CN–, rotenone, etc)  no ATP formation
Block ATP synthesis (no ADP, or inhibitor of ATP synthase-oligomycin) no electron flow
Oxidation and phoshorylation are connected processes.

20. Uncoupling Agents and Conditions
Allow electron flow with ATP synthesis
Example: 2,4-dinitrophenol (DNP)
Others: CCCP, ionophores, membrane disruption
2,4-Dinitrophenol is a classic uncoupling inhibitor that allows electron flow to continue but ATP is not made. Some medical doctors thought that it would be a good diet pill; burn calories and not make ATP. The patients not only lost weight but also their lives.

21. Efficiency of Oxidative Phosphorylation
Lots of energy available.

22. Observed P/O Ratios
But the current accepted is lower; 2.5 (2.3) and 1.5 (1.4).

23. Phosphorylation “Substrate-level” vs. “Respiration-linked”
Two kinds of phosphorylation - substrate during glycolysis and etc linked.

24. Bimetallic Fe-Cu Reaction Center
In cytochrome oxidase
Bimetallic electrodes.
Karp, Gerald. Cell and Molecular Biology, 2e

25. Cytochrome Oxidase http://www.pigment.unl.edu/bioc933/
Path of electrons in cytochrome oxidase. Within each of the component parts of the chain there are several sites for redox reactions.
metalloenzymes/Cyt%2OOxidase/
_COX_cycle.gif

26. Order of Carriers: Ascending Eo
The order of the carriers.

27. Reduced Forms of O2
Various reduced forms of oxygen.

28. Enzymatic Defenses Against O
Oxygen radicals can be toxic - enzymes destroy.

29. Vitamin E (Tocopherol)
Radical scavenger
Vitamin E is a radical scavenger and can prevent the accumulation of oxidized products. Aging brings oxidation and reducing agent lessen the oxidations.

30. The FoF1 Complex
The structure of the ATP synthase, complex V.