1. Stage 4: Electron Transport Chain
Cellular respiration
Stage 4:
Electron Transport Chain

2. Cellular respiration

3. A working muscle recycles over 10 million ATPs per second
Atp accounting so far …
Glycolysis  2 ATP
Kreb’s cycle  2 ATP
Life takes a lot of energy, need more than 4 ATP!
There’s got to be more!
I need a lot more ATP!
A working muscle recycles over 10 million ATPs per second

4. There is more! O2 Electron Transport Chain (ETC)
Series of proteins build into inner mitochondrial membrane
Along cristae
Contains transport proteins & enzymes
Transport of electrons down ETC are linked to the pumping of H+ ions to create an H+ gradient
Yields ~34 ATP per 1 glucose molecule
Only occurs in the presence of O2 (aerobic respiration) O2
That’s more like it!

5. mitochondria Double membrane Outer membrane Inner membrane
Highly folded cristae
Contains transport proteins & enzymes
Intermembrane space
Fluid-filled space between membranes
Remember:
Form fits
function!

6. Electron Transport Chain
Inner mitochondrial membrane
Intermembrane space C Q
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
Mitochondrial matrix

7. Remember the electron carriers?
Glycolysis --> 2 NADH
Kreb’s cycle  8 NADH
2 FADH2
Time to break open the piggybank!

8. Electron Transport Chain
NADH  NAD+ + H
Building proton gradient! p e
intermembrane space H+ H+ H+
inner mitochondrial membrane
H  e- + H+ C Q e– e– e– H
FADH2
FAD H 1 2
NADH
2H+ + O2
H2O
NAD+
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
mitochondrial matrix
What powers the proton (H+) pumps?…

9. Stripping H from electron carriers
Electron carriers pass electrons & H+ to ETC
H cleaved off NADH & FADH2
Electrons stripped from H atoms  H+
Electrons pass from one electron carrier to the next
Flowing electrons create energy to do work
Transport proteins in membrane pump H+ (protons) across the inner membrane to intermediate space
NAD+ Q C
NADH
H2O H+ e–
2H+ + O2
FADH2 1 2
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
FAD
TA-DA!!
Moving electrons do the work! H+
ADP + Pi
ATP

10. electrons flow downhill to O2
But what “pulls” the electrons down the ETC?
H2O O2
electrons flow downhill to O2
oxidative phosphorylation

11. Electrons flow downhill
Electrons move in steps from carrier to carrier downhill to oxygen
Each subsequent carrier is more electronegative
Controlled oxidation
Controlled release of energy
make ATP instead of fire!

12. We did it! Set up a H+ gradient
ADP + Pi
Set up a H+ gradient
Now need to let protons flow through ATP synthase
Synthesis ATP
ADP + Pi  ATP
Are we there yet?
ATP

13. Chemiosmosis links the Electron Transport Chain to ATP synthesis
The diffusion of ions across a membrane
Build up of proton gradient just so H+ could flow through ATP synthase enzyme to build ATP
Chemiosmosis links the Electron Transport Chain to ATP synthesis
Now we’re
talking
energy!
But how
much?

14. ATP Pyruvate from cytoplasm Intermembrane space Inner mitochondrial
Electron
transport
system C Q
NADH e-
2. Electrons provide energy to pump protons across the membrane. H+
1. Electrons are harvested and carried to the transport system. e-
Acetyl-CoA
NADH e-
H2O
Krebs
cycle e-
3. Oxygen joins with protons to form water. 1
FADH2 O2 2 O2 +
2H+
CO2 H+
ATP
ATP H+
ATP
4. Protons diffuse back in down their concentration gradient, driving the synthesis of ATP.
ATP
synthase
Mitochondrial
matrix

15. ~38 ATP
Cellular respiration
2 ATP
2 ATP
~34 ATP

16. Summary of cellular respiration
C6H12O6
6O2
6CO2
6H2O
~38 ATP  +
Where did the glucose come from?
Where did the O2 come from?
Where did the CO2 come from?
Where did the CO2 go?
Where did the H2O come from?
Where did the ATP come from?
What else is produced that is not listed in this equation?
Why do we breath?

17. cytochrome c oxidase complex
If oxygen is missing …
What is the final electron acceptor in the ETC?
So, what happens if O2 is unavailable?
Nothing pulls the electrons down the chain
ETC backs up
NADH & FADH2 can’t load H+
ATP production stops
Cells run out of energy
You die! O2
NAD+ Q C
NADH
H2O H+ e–
2H+ + O2
FADH2 1 2
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
FAD
Cyanide attaches to the final electron acceptor (fourth, but only three are shown). By binding to the protein, it can no longer accept electrons and the ETC is stopped … no more ATP are produced.

19. THAT’S IT!
We’re finally done.
Any questions?