2. The Role of Electron Transport in Metabolism
Electron transport is carried out by four closely related multisubunit membrane-bound complexes and two electron carriers, coenzyme ___ and cytochrome ___
In a series of oxidation-reduction reactions, electrons from FADH2 and NADH are transferred from one complex to the next until they reach _____
O2 is reduced to H2O
As a result of electron transport, ____________ are pumped across the inner membrane to the intermembrane space, creating a pH gradient

3. ATP Production in the Mitochondrion
The production of ATP in the mitochondria is the result of oxidative phosphorylation
The proton gradient establishes a voltage gradient
The proton and voltage gradients together provide the mechanism to couple electron transport with _______________________________________

4. Establishment of the Proton Gradient

5. Summary
Electron transport from one carrier to another creates a proton gradient across the inner mitochondrial membrane
The proton gradient is coupled to the production of ATP in aerobic metabolism

6. Reduction Potentials
A useful way to look at electron transport is to consider the change in free energy associated with the movement of electrons from one carrier to another
If we have two electron carriers, for example NADH and coenzyme Q, are electrons more likely to be transferred from NADH to coenzyme Q, or vice versa?
What we need to know is the _____________ _____________ for each carrier
A carrier of high reduction potential will tend to be _____________ if it is paired with a carrier of _____________ reduction potential

7. Reduction Potentials

8. Reduction Potentials

9. Summary
Standard reduction potentials provide a basis for comparison among redox reactions
The sequence of reactions in the electron transport chain can be predicted by using reduction potentials.

10. Electron Transport Complexes
Complex I: NADH-CoQ oxidoreductase
Electrons are passed from NADH to FMN
NADH + H+ E-FMN  NAD+ + E-FMNH2

11. Electron Transport Complexes
Electrons are then passed to the iron-sulfur clusters
The last step of Complex I involves electrons being passed to coenzyme Q (also called ubiquinone)

12. Energetics of Electron Transport
The transfer of electrons is strongly ____________ and sufficient to drive the phosphorylation of ADP

13. Electron Transport Complexes
Complex II: Succinate-coenzyme Q oxidoreductase
Succinate + E-FAD  Fumarate + E-FADH2
The overall reaction is exergonic (-13.5 kJ/mol), but not enough to drive ATP production
No H+ is pumped out of the matrix during this step

14. Electron Transport Complexes
Complex III: CoQH2-cytochrome c oxidoreductase
CoQH2 + 2Cyt c[Fe(III)]  CoQ + 2Cyt c[Fe(II)] + 2H+
This reactions of this complex results in a decrease in free energy that is sufficient to drive the phosphorylation of ADP to ATP
The flow of electrons from reduced CoQ, a quinone that can exist in 3 forms, is known as the _____________

15. Oxidized and Reduced Forms of CoQ

16. Electron Transport Complexes
Complex IV: Cytochrome c oxidase
Catalyzes the final step in electron transport
2Cyt c[Fe(II)] + 2H+ + ½O2  2 Cyt c[Fe(III)] + H2O
Complex IV contains cytochrome a, cytochrome a3, and Cu(II), which are also involved in the electron transport
Complex IV is the link to __________ __________

17. Electron Flow

18. The Energetics of Electron Transport Reactions

19. The Heme Group of Cytochromes
All cytochromes contain a _____________ group
Side chain differences depending on the heme

20. Connection between Electron Transport & Phosphorylation
The energy-releasing oxidations give rise to proton pumping and a pH gradient across the _____________ _____________ membrane
Differences in the concentration of ions across the membrane generates a _____________ _____________
A coupling process converts the electrochemical potential to the chemical energy of ATP
The coupling factor is ATP _____________, a complex protein oligomer, separate from the electron transport complexes
Uncouplers inhibit the phosphorylation of ADP without affecting electron transport; examples are ________________, _____________, & _____________

21. Uncouplers

22. P/O Ratio
P/O ratio: the number of moles of Pi consumed in _____________ to the number of moles of oxygen atoms consumed in _____________
Phosphorylation: ADP + Pi  ATP + H2O
Oxidation: 1/2O2 + 2H+ + 2e-  H2O
P/O = ______ when NADH is oxidized
P/O = ______ when FADH2 is oxidized

23. Summary
The coupling of electron transport to oxidative phosphorylation requires a multisubunit membrane-bound enzyme, ATP synthase.
This enzyme has a channel for protons to flow from the intermembrane space into the mitochondrial matrix.
The proton flow is coupled to ATP production in a process that appears to involve a conformational change of the enzyme.

24. Chemiosmotic Coupling
based on a ________ concentration gradient between the intermembrane space and the matrix
a proton gradient exists because the various proteins that serve as electron carriers are not symmetrically oriented with respect to the two sides of the inner mitochondrial membrane
these proteins take up protons from the matrix when they are reduced and release them to the intermembrane space when they are reoxidized
the reactions of NADH, CoQ, and O2 all require _______________________

25. Chemiosmotic Coupling

26. Chemiosmotic Coupling
Evidence for chemiosmotic coupling suggested (Mitchell 1961):
A system with definite inside and outside _____________ (closed vesicles) is essential.
Submitochondrial vesicles can be prepared, which carry out oxidative phosphorylation and have an asymmetric orientation of respiratory complexes.
A model system for oxidative phosphorylation can be constructed with proton pumping in the absence of electron transport; the model system consists of reconstituted membrane vesicles, mitochondrial ATP synthase, and a proton pump.
The existence of the pH gradient has been demonstrated and _____________ _____________

27. Chemiosmotic Coupling
The mechanism by which the proton gradient leads to the production of ATP depends on ion channels through the inner mitochondrial membrane
Protons flow back into the matrix through channels in the F0 unit of ATP _____________
The flow of protons is accompanied by formation of ATP in the F1 unit of ATP _____________
The details of how phosphorylation takes place as a result of the linkage to the proton gradient are not explicitly specified by this mechanism

28. Chemiosmotic Coupling

29. Conformational Coupling
The proton gradient leads to changes in conformation in a number of proteins, including ATP _______________
There are 3 sites for substrate on ATP _____________, and 3 possible conformations:
- Open (O); a low affinity for substrate
- Loose-binding (L); not catalytically active, binds ADP & Pi
- Tight-binding (T); catalytically active, binds ATP
These sites interconvert as a result of proton flux through ATP synthase
Proton flux converts L to T, which produces ATP
Proton flux converts T to O, releasing ATP

30. Release of ATP from ATP Synthase

31. Summary
In chemiosmotic coupling, the proton gradient is the crux of the matter. The flow of protons through pores in the synthase drives ATP production.
In conformational coupling, a change in the shape of the synthase releases bound ATP that has already been formed.

32. Respirator Inhibitors & Electron Transport
Respiratory inhibitors can be used to determine the order of reactions in the electron transport chain
Isolate intact _____________ from cells
Provide an oxidizable substrate so that electron transport can occur
Add a respiratory inhibitor
Measure relative amounts of oxidized and reduced forms of various electron carriers
Inhibitors have an effect on three sites in the electron transport chain

33. The Effect of Respiratory Inhibitors

34. Sites of Action of Some Respiratory Inhibitors

35. Shuttle Mechanisms
Shuttle mechanisms: transport metabolites between _____________ and _____________
Glycerol phosphate shuttle:
We know glycolysis in the _____________ produces NADH
NADH does not cross the _____________________ membrane, but glycerol phosphate and dihydroxyacetone phosphate do
Through the glycerol phosphate shuttle, ____ ATP are produced in the mitochondria for each cytosolic NADH

36. The Glycerol-Phosphate Shuttle

37. The Malate-Aspartate Shuttle
Has been found in mammalian kidney, liver, and heart
Malate crosses the mitochondrial membrane, while oxaloacetate cannot
The transfer of electrons from NADH in the cytosol produces NADH in the mitochondria
In the malate-aspartate shuttle, _____ mitochondrial ATP are produced for each cytosolic NADH

38. The Malate-Aspartate Shuttle

39. Summary
Shuttle mechanisms transfer ___________, but not _____________, from the cytosol across the mitochondrial membrane
In the malate-aspartate shuttle, 2.5 molecules of ATP are produced for each molecule of cytosolic NADH, rather than 1.5 ATP in the glycerol-phosphate shuttle…
This affects the overall yield of ATP in these tissues

40. ATP Yield from Complete Oxidation of Glucose
In the complete oxidation of glucose, a total of ______ or ______ molecules of ATP are produced for each molecule of glucose, depending on the shuttle mechanism

41. The ATP Yield from Complete Oxidation of Glucose