Oxidative phosphorylation occurs in the inner mitochondrial membrane and involves the formation of ATP using energy released from the transfer of electrons through electron carriers and protein complexes. This electron transfer is coupled to ATP synthesis by the generation of a proton gradient across the inner mitochondrial membrane. The flow of protons back through ATP synthase drives the phosphorylation of ADP to form ATP. Regulation of oxidative phosphorylation controls the rate of ATP production to match cellular energy needs.

1. Oxidative Phosphorylation

2. General Considerations
• How do we define oxidative
phosphorylation?
– formation of ATP using the energy released by
the transfer of electrons from NADH and
FADH2 through a series of electron carriers
• What couples the formation of ATP to the
transfer of electrons?
– a proton gradient

3. General Considerations
• Where in the cell does oxidative
phosphorylation take place?
– inner mitocondrial membrane
• What do we know about the mitocondrial
membranes?
– outer membrane – reasonably permeable
• contains porins – VDAC
– inner membrane – relatively impermeable

4. Origin of Mitocondria
• What is the believed origin of mitocondria?
– endosymbiosis
• What evidence supports this idea?
– mitcondrial DNA
– machinery for transcription and translation
– similarity of genome to bacteria

5. Redox Potentials and Free
Energy Changes
• How does one determine the redox potential of a
substance?
sample half-cell
standard reference half-cell

6. Redox Potentials and Free
Energy Changes
• What is the relationship between change in redox
potential and change in free energy?
– G01 = -nF E1
0
• n = number of electrons transferred
• F =faraday (constant, 23.06 kcal/mole/volt)
– Can calculate free energy change from reduction
potentials of the reactants
• By knowing the electron transfer potential of
NADH relative to O2 one can calculate the amount
of free energy released when O2 is reduced by
NADH.

7. Redox Potentials and Free
Energy Changes
• One can also quantify the energy associated
with a proton gradient.
– G = RTln(c2/c1) + ZF V
• c2 = concentration on one side of membrane
• c1 = concenetration on other side of membrane
• Z = electrical charge of transported material
• F = Faraday constant (23.06 kcal/mole/volt)

8. Electron Transport
• What determines the rate of electron transport?
– distance between donor and acceptor

9. Electron Transport
– driving force or free energy change

10. Electron Transport
• What are the
complexes making up
the respiratory chain?
– three proton pumps
– one link to citric acid
cycle

11. Electron Transport
• What is the role of ubiquinone or coenzyme Q?

12. Electron Transport
• What happens to the electrons from NADH?
– enter ETS at NADH-Q oxidoreductase

13. Electron Transport
• Initial step is transfer of electrons to FMN a
prosthetic group of the enzyme

14. Electron Transport
• Electrons are then transferred to iron-sulfur
clusters another prosthetic group

15. Electron Transport
• Electrons from clusters transferred to
coenzyme Q
– as a result of electron transfer four protons are
pumped out of mitocondrial matrix
• Reaction summarized:
– NADH + Q + 5H+
matrix  NAD+ + QH2 + 4H+cytosol

16. Electron Transport
• Coenzyme Q also serves as entry point for
electrons from FADH2 from oxidation of
succinate
– succinate-Q reductase complex
• inner mitocondrial membrane
• FADH2 transfers electrons to iron-sulfur
clusters then to Q
– no protons are pumped

17. Electron Transport
• Q-cytochrome c oxidoreductase catalyzes
the transfer of electrons from Q to
cytochrome c
– What is a cytochrome?
• electron transferring protein with heme prosthetic
group
• transfers only electrons
• iron in heme goes between Fe+2 and Fe+3

18. Electron Transport
• Q-cytochrome c
oxidoreductase
contains 3 hemes and
a iron-sulfur cluster

19. Electron Transport
• What is the Q cycle?
– mechanism of coupling of electron transfer from Q to
cytochrome c to proton transport

20. • What is the function of cytochrome c
oxidase?
– reduction of oxygen to water
• What are the major prosthetic groups of this
complex?
– CuA/CuA
– heme a
– heme a3-Cub
Electron Transport

21. Cytochrome c Oxidase

22. Cytochrome c Oxidase
• Mechanism of action

23. Cytochrome c Oxidase
• cytochrome c oxidase
pumps four additional
protons from matrix
for a total of eight
protons removed from
matrix

24. Electron Transport System

25. Electron Transport System

26. Electron Transport
• Toxic derivatives of molecular oxygen may
be formed by partial reduction
O2  O2
_
 O2
_
2
superoxide
anion
peroxide

27. Electron Transport
• How does the cell protect itself against
these reactive oxygen species?
– makes use of superoxide dismutase and catalase
– 2O2
_
+ 2H+  O 2 + H2O2
– 2H2O2  O2 + 2H2O

28. ATP Synthesis
• What is the chemiosmotic hypothesis?
– ATP synthesis and electron transport are coupled by
proton gradient across mitocondrial membrane

29. ATP Synthesis
• What is ATP synthase
and what do we know
about its structure?
– consists of F1 and F0
– F1 has 5 types of
polypeptide chains
• 3,3,,,
– F0 contains proton
channel
• 10-14 c subunits
• a,b2 subunits

30. • How is ATP synthesized?
ATP Synthesis

31. • What is the role of the proton gradient in ATP synthesis?
– part of binding-change mechansm
• 3  subunits promote ADP & P binding, ATP synthesis, ATP release
ATP Synthesis

32. ATP Synthesis
• How does proton flow
through F0 drive the
rotation of the 
subunit?
– each c subunits
consists of 2  helices
with one helix
containing an aspartic
acid residue
– a subunit contains two
proton half channels

33. ATP Synthesis
• Proton enters half-channel, neutralizes charge on aspartate
• c can rotate clockwise
• proton can move into matrix

34. ATP Synthesis
• Since c ring is linked to  and  subunits, as
c turns these subunits rotate
– rotation protmotes synthesis of ATP via
binding-change mechanism
– each 3600 rotation of  subunit leads to
synthesis of 3 ATP’s
• 10 protons generate 3 ATP’s
• each ATP requires transport of about 3 protons

35. Mitocondrial Shuttles
• Reoxidation of
cytosolic NADH
requires shuttle
mechanism
– glycerol 3-phosphate
shuttle
• found in muscle

36. Mitocondrial Shuttles
• malate-aspartate shuttle
– heart and liver

37. Mitocondrial Shuttles
• What is an ATP-ADP translocase?
– transport protein allowing ATP to exit mitocondrion and
ADP to enter
– result in moving one negative charge out of matrix
• decreases proton motive force

38. Mitocondrial Shuttles
• Other mitocondrial transport proteins act as
shuttles

39. Regulation of Respiration
• Energy formed from
oxidation of glucose
• 3 protons = 1 ATP
• 1 proton used to move
ATP
• one pair of electons
from NADH = 2.5
molecules of ATP

40. Regulation of Respiration
• What controls rate of electron transport?

41. Regulation of Respiration
• Oxidative
phosphorylation can
be inhibited by many
substances

42. Regulation of Respiration
• What are uncoupling agents?
– transport protons across mitocondrial membrane

43. Regulation of Respiration
• Does uncoupling serve any useful purpose?
– body heat generation