1. Chapter 9. Cellular Respiration STAGE 1: Glycolysis

2. glucose      pyruvate
Glycolysis
Breaking down glucose
“glyco – lysis” (splitting sugar)
most ancient form of energy capture
starting point for all cellular respiration
inefficient
generate only 2 ATP for every 1 glucose
in cytosol
why does that make evolutionary sense?
glucose      pyruvate 6C 2x 3C
Life on Earth first evolved without free oxygen (O2) in atmosphere
energy had to be captured from organic molecules in absence of O2
Organisms that evolved glycolysis are ancestors of all modern life
all organisms still utilize glycolysis

3. Glycolysis summary invest some ATP harvest a little more ATP
& a little NADH
Glucose is a stable molecule it needs an activation energy to break it apart.
phosphorylate it = Pi comes from ATP.
make NADH & put it in the bank for later.
P is transferred from PEP to ADP
kinase enzyme
ADP  ATP

4. How is NADH recycled to NAD+?
Another molecule must accept H from NADH
aerobic respiration
ethanol fermentation
lactic acid fermentation
NADH

5. Anaerobic ethanol fermentation
Bacteria, yeast 1C 3C 2C
pyruvate  ethanol + CO2
NADH
NAD+
beer, wine, bread
at ~12% ethanol, kills yeast
Animals, some fungi
Count the carbons!!
Lactic acid is not a dead end like ethanol. Once you have O2 again, lactate is converted back to pyruvate by the liver and fed to the Kreb’s cycle.
pyruvate  lactic acid 3C
NADH
NAD+
cheese, yogurt, anaerobic exercise (no O2)

6. Pyruvate is a branching point
fermentation
Kreb’s cycle
mitochondria

7. Pyruvate oxidized to Acetyl CoA
reduction
Release CO2 because completely oxidized…already released all energy it can release … no longer valuable to cell….
Because what’s the point?
The Point is to make ATP!!!
oxidation
Yield = 2C sugar + CO2 + NADH

8. reduction of electron carriers
Count the carbons & electron carriers!
pyruvate 3C 2C
acetyl CoA
citrate 4C 6C
NADH x2 4C 6C
This happens twice for each glucose molecule
CO2
reduction of electron carriers
NADH 5C 4C
CO2
FADH2 4C 4C
NADH
ATP

9. What’s so important about NADH?
NADH & FADH2
Krebs cycle produces:
8 NADH
2 FADH2
2 ATP
Let’s go to ETC…
What’s so important about NADH?

10. So why the Krebs cycle? If the yield is only 2 ATP, then why?
value of NADH & FADH2
electron carriers
reduced molecules store energy!
to be used in the Electron Transport Chain

11. 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!
Why stop here…
There’s got
to be more to
life than this.

12. Last stop and most important!
Electron Transport Chain
series of molecules built into inner mitochondrial membrane
mostly transport (integral) proteins
transport of electrons down ETC linked to ATP synthesis
yields ~34 ATP from 1 glucose!
only in presence of O2 (aerobic)
That sounds more like it!

13. Don’t forget the Mito! Double membrane * form fits function!
outer membrane
inner membrane (ETC here!)
highly folded cristae*
fluid-filled space between membranes = intermembrane space
Matrix (Kreb’s here!)
central fluid-filled space
* form fits function!

14. Electron Transport Chain

15. Remember the NADH? Kreb’s cycle Glycolysis 8 NADH 2 FADH2 2 NADH PGAL

16. Electron Transport Chain or Chemiosmosis
NADH passes electrons to ETC
H cleaved off NADH & FADH2
electrons stripped from H atoms  H+ (H ions)
electrons passed from one electron carrier to next in mitochondrial membrane (ETC)
transport proteins in membrane pump H+ across inner membrane to intermembrane space
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.

17. electrons flow downhill to O2
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
electrons flow downhill to O2

18. 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

19. Why the build up H+? ATP synthase ADP + Pi  ATP
enzyme in inner membrane of mitochondria
ADP + Pi  ATP
only channel permeable to H+
H+ flow down concentration gradient = provides energy for ATP synthesis
molecular power generator!
flow like water over water wheel
flowing H+ cause change in shape of ATP synthase enzyme
powers bonding of Pi to ADP
“proton-motive” force

20. Cellular respiration

21. Metabolism Coordination of digestion & synthesis Digestion
by regulating enzyme
Digestion
digestion of carbohydrates, fats & proteins
all catabolized through same pathways
enter at different points
cell extracts energy from every source
CO2

22. Summary of cellular respiration
C6H12O6
6O2
6CO2
6H2O
~36 ATP  +
Where did the glucose come from?
Where did the O2 come from?
Where did the CO2 come from?
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 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!

23. 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?