1. Lecture: Krebs Cycle and Electron Transport Chain

2. Aerobic Respiration
Krebs Cycle
Glycolysis gets about 2% of the energy out of glucose, even with fermentation, 90% of the energy is still available in the form of compounds
Oxygen is a powerful electron acceptor and is the key to unlocking more energy
Glycolysis
1 6-C sugar + 2ATP 2 3-C sugars 
2 Pyruvic Acids + 4ATP + 2NADH
In the presence of oxygen Pyruvic acid enters the Krebs cycle
2 ATP O2
Glucose
Glycolysis
2 Pyruvic Acid
4 ATP
2 NADH
No O2
Alcohol
Fermentation
Lactic Acid
Fermentation

3. Krebs Cycle

4. Summary of the Krebs Cycle
Pyruvic acid is broken down into CO2 in a series of energy releasing steps
Takes place in the mitochondria
1 atom of C from pyruvic acid becomes CO2 and is released into the air. NAD+ becomes NADH
The other 2 atoms of C join Coenzyme A to form Acetyl Co-A
2-C Acetyl Co-A joins 4-C sugar to form Citric Acid (6-C compound, Coenzyme A is released)
6-C compound broken into a 5-C compound, releasing more CO2 and NADH
5-C compound broken into a 4-C compound, releasing more CO2, ATP and NADH
4-C compound turns back into 4-C sugar from step 5, releases FADH2 and NADH

5. Totals per 1 Glucose (so far)
Anaerobic Respiration (Fermentation)
Aerobic Respiration (Cellular Respiration)
ATP =
NADH =
FADH2 = 2 4 2 10 2
Alcohol
Fermentation
Lactic Acid
Fermentation
2 ATP
No O2
Glycolysis
2 Pyruvic Acid
Glucose
2 NADH
4 ATP O2
There is still a lot of energy left to be unleashed!

6. Aerobic Respiration (Cellular Respiration)
So Why Do We Need O2?
ATP is the energy that is readily used by cells
Carrier molecules can be converted into ATP in the presence of oxygen!
How? Another electron transport system (like photosynthesis)
How many carrier molecules were formed in glycolysis and the Krebs cycle?
There are 12 high energy
molecules ready to be
converted into ATP in the
electron transport chain!
Aerobic Respiration (Cellular Respiration)
ATP = 4
NADH = 10
FADH2 = 2

7. Electron Transport Chain
High energy electrons transferred from NADH and FADH2 into the electron transport chain
Occurs in the inner membrane of the mitochondria
As high energy e-s pass along the transport chain, H+ are transported into the intermembrane space
An enzyme at the end combines low energy e-s with H+ and O2 to make water (this is why we need O2!)
ATP synthase allows H+ out of the intermembrane space, and uses the energy to make ATP

8. So now how much ATP per Glucose?
Each carrier molecule provided energy to make 2 to 3 ATP molecules
FADH2 makes 2
NADH from glycolysis makes 2, NADH from Krebs cycle makes 3
Glycolysis
Krebs Cycle
Electron Transport Chain
ATP =
NADH =
FADH2 =
ATP already made =
ATP from NADH =
ATP from FADH2 =
Total = 2 2 4 28 2 8 2 4
36!
That’s it for anaerobic!