1. Cellular Respiration Part 2: The Transition Reaction Part 3: Krebs Cycle

2. Part 2: Transition Reaction
Remember, glycolysis took a 6 carbon glucose molecule and produced two 3 carbon pyruvates, a net of 2 ATP molecules, H2O and NADH
In this step the end products of glycolysis, the 2 pyruvate molecules, are moved from the cytoplasm into the mitochondria for further energy “harvesting”.

3. this occurs across both the outer and inner mitochondrial membranes
TRANSITION REACTION
this occurs across both the outer and inner mitochondrial membranes
Decarboxylation
NAD+ reduced to energized NADH + H+
coenzyme A added to pyruvate forming AcetylCoA
Coenzyme A needs Vitamin B5 or pantothenic acid

4. Part 3: Krebs Cycle
This is also called the Citric Acid Cycle or the Tricarboxylic Acid Cycle (TCA)
The purpose is to slowly oxidize a pyruvate molecule and “harvest” the bond energy in small amounts
The energy released in the catabolism of the pyruvate is stored in NADH, FADH2 and ATP via GTP (guanine triphosphate)
Named after Sir Hans Adolph Krebs – co-recipient of Nobel prize in physiology in 1953
Jewish doctor and researcher banned from practicing medicine by the Nazi’s so immigrated to Britain
- knighted for his work on CAC and urea cycle the year I was born

5. 1. KREBS CYCLE starts
acetyl CoA bonds to 4C oxaloacetate forming a 6C citrate
a water is required
the coenzyme A is released to be reused

6. 2. Isomerization
- This happens so the next reaction requires less energy

7. 3. Harvest Energy
Decarboxylation
an NAD+ is reduced to an energized NADH + H+
this is from the energy “harvested” during the decarboxylation and oxidation of isocitrate

8. 4. More Energy is “Harvested”
Decarboxylation
another NAD+ is reduced to NADH + H+
this is from the energy “harvested” during the decarboxylation and the oxidation of  keto glutarate
note again the addition of a coenzyme A to the product

9. 5. Harvest More Energy
The release of the coenzyme A and the isomerization provides energy to phosphorylate a GDP to a GTP
The GTP is used to phosphorylate an ADP to an ATP
these are both examples of substrate level phosphorylation, where the phosphorylation energy comes from breaking the bonds of another molecule

10. 6. It’s all about the energy STOOPID!!
FAD is reduced to an energized FADH2
the energy comes from oxidation of succinate
another coupled redox reaction!!

11. 7. What Energy?
- adding a water hydrolyses the double bond

12. 8. Yeah – More Energy!!
again an NAD+ is reduced to energized NADH + H+
the 4 carbon oxaloacetate molecule is regenerated
Note that of the 3 CO2 molecules generated only the first one actually removed a carbon from the original pyruvate
The 2nd and 3rd carbons removed were from previous pyruvate molecules

13. Transition Reaction and Krebs Cycle - SUMMARY
For each molecule of pyruvate the Krebs Cycle turned once and:
Required 2 H2O and CoA
Generated 1 ATP, 4 NADH, 1 FADH2, 4H+ and released 3 CO2
Double all these products for a glucose!

14. Finally,
For a test you will be given the Krebs Cycle with the main molecules and you will have to name reactions and complete all the molecules on the coupled reaction arrows.
Next, how does the cell get ATP energy from the energized NADH and FADH2?