1. Cellular Respiration Oxidation of Pyruvate Krebs Cycle

2. Glycolysis is only the start
Pyruvate has more energy to yield
3 more C to strip off (to oxidize)
if O2 is available, pyruvate enters mitochondria
enzymes of Krebs cycle complete oxidation of sugar to CO2 2x 6C 3C
glucose      pyruvate
Can’t stop at pyruvate == not enough energy produced
Pyruvate still has a lot of energy in it that has not been captured.
It still has 3 carbons! There is still energy stored in those bonds.
pyruvate       CO2 3C 1C

3. Cellular respiration

4. Recall: Structure of Mitochondria

5. Membrane-bound Enzymes

6. pyruvate    acetyl CoA + CO2
Oxidation of pyruvate
Pyruvate enters mitochondria
3 step oxidation process
releases 1 CO2 (count the carbons!)
reduces NAD  NADH (stores energy)
produces acetyl CoA
Acetyl CoA enters Krebs cycle ( inside cristae)
where does CO2 go?
NAD
NADH 3C 2C 1C
pyruvate    acetyl CoA + CO2 [ 2x ]
CO2 is fully oxidized carbon == can’t get any more energy out it
CH4 is a fully reduced carbon == good fuel!!!
Waiting to exhale?

7. Pyruvate oxidized to Acetyl CoA
Onto Krebs
reduction
oxidation
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!!!
Yield = 2C sugar + CO2 + NADH
Count sugars!

8. Pryruvic acid (pyruvate) crosses cristae MB
Determine where the mbs
are located (inner and outer) of the mitochondria on this picture!

9. Krebs cycle 1937 | 1953 aka Citric Acid Cycle
in mitochondrial matrix
8 step pathway
each catalyzed by specific enzyme
step-wise catabolism of 6C citrate molecule
Evolved later than glycolysis
does that make evolutionary sense?
bacteria 3.5 billion years ago (glycolysis)
free O2 2.7 billion years ago (photosynthesis)
eukaryotes 1.5 billion years ago (aerobic (oxygen) respiration (organelles)
Hans Krebs

10. Count the carbons! x2 3C 2C 4C 6C 4C 6C 5C 4C 4C 4C
pyruvate 3C 2C
acetyl CoA
citrate 4C 6C x2 4C 6C
This happens twice for each glucose molecule
oxidation of sugars
CO2 5C 4C
CO2 4C 4C

11. reduction of electron carriers
Count the 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

12. Glucose is now fully oxidized!
C6H12O6 
CO2
& ended up with 4 ATP!
What’s the Point?

13. What’s so important about NADH?
NADH & FADH2
Krebs cycle produces large quantities of electron carriers
NADH
FADH2
stored energy!
go to ETC
What’s so important about NADH?

14. Energy accounting of Krebs cycle[
Energy accounting of Krebs cycle ]
Net gain = 2 ATP
= 8 NADH + 2 FADH2
4 NAD + 1 FAD
4 NADH + 1 FADH2 2x
pyruvate          CO2
1 ADP
1 ATP 3C 3x 1C

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

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

17. Any Questions??