1. Cellular Respiration Stage 4: Electron Transport Chain
Modified from Kim Foglia

2. Cellular respiration

3. What’s the point?
ATP
The Point is to Make ATP!

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

5. There is a better way! O2 Electron Transport Chain
series of molecules built into inner mitochondrial membrane
mostly transport proteins
transport of electrons down ETC linked to ATP synthesis
yields ~32-34 ATP from 1 glucose!
only in presence of O2 (aerobic) O2

6. Mitochondria Matrix Double membrane central fluid-filled space
outer membrane
inner membrane
highly folded cristae
fluid-filled space between membranes = intermembrane space

7. Electron Transport Chain
Inner mitochondrial membrane
Intermembrane space C Q
NADH dehydrogenase
Cytochrome bc complex
Cytochrome oxidase complex
Mitochondrial matrix

8. Time to break open the bank!
Remember the NADH?
Krebs cycle
Glycolysis
G3P
8 NADH
2 FADH2
4 NADH
Time to break open the bank!

9. Electron Transport Chain
What powers the proton pumps??
Inner mitochondrial membrane
Intermembrane space H+ H+ H+
H  e- + H+ C Q e– e– e–
FADH2 H
FAD 1 2
NADH
2H+ + O2
NAD+
H2O
NADH dehydrogenase
Cytochrome bc complex
Cytochrome oxidase complex
Mitochondrial matrix

10. Electron Transport Chain
NADH passes electrons to ETC
H cleaved off NADH & FADH2
electrons stripped from H atoms  H+ (protons)
electrons passed from one electron carrier to next in mitochondrial membrane (ETC)
transport proteins in membrane pump H+ across inner membrane to intermembrane space
NAD+ Q C
NADH
H2O H+ e–
2H+ + O2
FADH2 1 2
NADH dehydrogenase
bc1 complex
Cytochrome oxidase complex
FAD H+
Oxidation refers to the loss of electrons to any electron acceptor, not just to oxygen.
Uses exergonic flow of electrons through ETC to pump H+ across membrane.
ADP + Pi
ATP

11. O2 is 2 oxygen atoms both looking for electrons
But what “pulls” the electrons down the ETC?
Pumping H+ across membrane … what is energy to fuel that?
Can’t be ATP! that would cost you what you want to make!
Its like cutting off your leg to buy a new pair of shoes. :-(
Flow of electrons powers pumping of H+
O2 is 2 oxygen atoms both looking for electrons
oxidative phosphorylation

12. Electrons flow downhill
Electrons move in steps from carrier to carrier downhill to O2
each carrier more electronegative
controlled oxidation
controlled release of energy
Electrons move from molecule to molecule until they combine with O & H ions to form H2O
It’s like pumping water behind a dam -- if released, it can do work

13. “proton-motive” force
We did it! H+
ADP + Pi
Set up a H+ gradient
Allow the protons to flow through ATP synthase
Synthesizes ATP
ADP + Pi  ATP
ATP

14. 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
Chemiosmosis is the diffusion of ions across a membrane. More specifically, it relates to the generation of ATP by the movement of hydrogen ions across a membrane.
Hydrogen ions (protons) will diffuse from an area of high proton concentration to an area of lower proton concentration. Peter Mitchell proposed that an electrochemical concentration gradient of protons across a membrane could be harnessed to make ATP. He likened this process to osmosis, the diffusion of water across a membrane, which is why it is called chemiosmosis.

15. Peter Mitchell 1961 | 1978 Proposed chemiosmotic hypothesis
revolutionary idea at the time
proton motive force

16. Pyruvate from cytoplasm synthase Krebs cycle Mitochondrial matrix+ Q C 32
ATP 2
Pyruvate from
cytoplasm
Electron
transport
system
synthase
H2O
CO2
Krebs
cycle
Intermembrane
space
Inner
mitochondrial
membrane
1. Electrons are harvested and carried to the transport system.
2. Electrons provide energy to pump protons across the membrane.
3. Oxygen joins with protons to form water.
2H+
NADH
Acetyl-CoA
FADH2
4. Protons diffuse back in
down their concentration
gradient, driving the
synthesis of ATP.
Mitochondrial
matrix 1 e-

17. 38 ATP
Cellular respiration + + +
2 ATP
~2 ATP
2 ATP
~32-34 ATP

18. 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 breathe?
Where did the glucose come from?
from food eaten
Where did the O2 come from?
breathed in
Where did the CO2 come from?
oxidized carbons cleaved off of the sugars
Where did the CO2 go?
exhaled
Where did the H2O come from?
from O2 after it accepts electrons in ETC
Where did the ATP come from?
mostly from ETC
What else is produced that is not listed in this equation?
NAD, FAD, heat!

19. Taking it beyond…
What is the final electron acceptor in electron transport chain? O2
So what happens if O2 unavailable?
ETC backs up
ATP production ceases
cells run out of energy
and you die!
What if you have a chemical that punches holes in the inner mitochondrial membrane?

20. What’s the point?
ATP
The Point is to Make ATP!

21. Summary