1. Cellular Respiration Stage 4: Electron Transport Chain

2. Cellular respiration

3. What’s the point?
The point is to make ATP!
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!
I need a lot more ATP!
A working muscle cell recycles over 10 million ATPs per second

5. That sounds more like it!
There is a better way!
Electron Transport Chain
series of proteins built into the inner mitochondrial membrane
along cristae
It’s basically a bunch of transport proteins & enzymes
This part of Cell Respiration yields ~32 ATP from 1 glucose!
Add the 4 we got from the other parts of resp and you get 36 total
BUT, it only works when in presence of O2 (aerobic respiration)
But HOW does it WORK??
That sounds more like it! O2

6. MUST understand the anatomy of the Mitochondrion
Double membrane
outer membrane
inner membrane
highly folded cristae
enzymes & transport proteins embedded here
intermembrane space
fluid-filled space between membranes
mitochondrial Matrix
Fluid-filled center
Citric Acid Cycle here
Oooooh! Form fits function!

7. Electron Transport Chain
Inner mitochondrial membrane
Intermembrane space C Q
ubiquinone
Cytochrome c
NADH dehydrogenase
Cytochrome c
reductase complex
cytochrome c oxidase complex
Mitochondrial matrix

8. Remember the Electron Carriers?
glucose
Krebs cycle
Glycolysis
G3P
2 NADH
8 NADH
2 FADH2
LET’S GO!! It’s
Almost time!
NADH & FADH2

9. The Importance of Redox Reactions
The only way that electrons (and their energy) can be transferred from one molecule to another, is if the molecule RECEIVING the electrons “LOVES” electrons MORE than the molecule that actually HAS the electrons.
What’s that word for molecules that “LOVE” electrons???
ELECTRONEGATIVE

10. So…Riddle me this, Batman:
Who must “LOVE” electrons MORE:
NADH OR the ETC
The ETC
How do you know this?
Because the ETC is able to strip the electrons from the NADH

11. Another Riddle:
Where would those same electrons have MORE potential energy?
With the NADH OR with the ETC G3P, because every time an electron moves from a LESS electronegative molecule to a MORE electronegative molecule, it LOSES a little energy (just like a ball falling off a table onto the floor)
Why do the electrons lose energy when they are with a more electronegative molecule?
Because they are MORE stable, and harder to move from the more electronegative molecule. It has a “tighter grip” on them (just like the floor has a “tighter grip” than the table). There’s no where for the electrons to go. They certainly won’t move back to the less electronegative compound (just like the ball won’t roll on its own back up to the table top).

12. One more… NADH gets oxidized / reduced by the ETC (pick one)
OXIDIZED because it LOSES it’s electrons to the ETC
The ETC gets oxidized / reduced by NADH (pick one)
REDUCED because it GAINS electrons from NADH

13. So…Electrons flow “downhill”
Electrons move in steps from a LESS electronegative carrier in the ETC to a MORE electronegative carrier in the ETC.
controlled oxidation
controlled release of energy
make ATP instead of fire!
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

14. So…
In the chain of electron carriers (ETC), Give the letter that shows the MOST electronegative carrier
In the chain of electron carriers (ETC), Give the letter that shows the LEAST electronegative carrier A B

15. What is the MOST ELECTRONEGATIVE thing we know (at least in bio class)?
OXYGEN!

16. O2 So, what “pulls” the electrons down the ETC? Oxygen!! H2O e-
We’re HERE!!! e-
H2O
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 O2
Oxygen!!
electrons flow downhill to O2
What’s made when the electrons (and some hydrogens) hit the oxygen?

17. What happens…
To the energy of the electrons as they are passed from carriers “higher” in the ETC to carriers “lower” in the ETC (ultimately to oxygen)?
Their energy is LOST
But is this energy just LOST???
NO!!
This energy is used to DO something!

18. What is the energy of the electrons used to do?
The electron carriers also serve as proton pumps.
These pumps move hydrogen ions from the matrix (LOW concentration) to the intermembrane space (HIGH concentration)
AGAINST their concentration gradient
WHY??
To create a source of potential energy
H+ ions trapped in area of HIGH concentration flow to LOW concentration, if ONLY they could get through the inner membrane

19. Electron Transport Chain
Building proton gradient!
NADH  NAD+ + H 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?…

20. Stripping H from Electron Carriers
Electron carriers pass electrons & H+ 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)
flowing electrons = energy to do work
transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space
NAD+ Q C
NADH
H2O H+ e–
2H+ + O2
FADH2 1 2
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
FAD
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. H+
TA-DA!!
Moving electrons do the work! H+ H+ H+
ADP + Pi
ATP

21. “proton-motive” force
And FINALLY… H+
ADP + Pi
The set up of the H+ gradient by the proton pumps allows the protons to flow from HIGH to LOW through ATP synthase
THIS SYNTHESIZES ATP!!! (and LOTS of it!)
ADP + Pi  ATP
ATP
Are we there yet?

22. Animations Electron Transport Chain (V Cell) ATP Synthase (V Cell)
Mitochondrion (Biovisions - Harvard)

23. 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.
So that’s the point!

24. Oxidative Phosphorylation
Oxidative phosphorylation uses the power of oxygen and chemiosmosis to create LOTS of ATP using ATP synthase
Substrate Level Phosphorylation relies on an enzyme physically stripping a Pi from one substrate and sticking to an ADP to make ATP
Much less efficient

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

26. 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

27. ~38 ATP
total
Cellular respiration + +
2 ATP
2 ATP
~34 ATP

28. Summary of cellular respiration
C6H12O6
6O2
6CO2
6H2O
~40 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 (Krebs Cycle)
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!

29. cytochrome c oxidase complex
NAD+ Q C
NADH
H2O H+ e–
2H+ + O2
FADH2 1 2
NADH dehydrogenase
cytochrome bc complex
cytochrome c oxidase complex
FAD
Taking it beyond…
What is the final electron acceptor in Electron Transport Chain? O2
So what happens if O2 unavailable?
ETC backs up
nothing to pull electrons down chain
NADH & FADH2 can’t unload H
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?

30. What’s the point?
The point is to make ATP!
ATP