1. The Kreb’s Cycle and Electron Transport
Chapter 9 Cellular Respiration

2. Kreb’s Cycle Introduction
At end of glycolysis, about 90% of the chemical energy that was available in glucose is still unused
To extract that energy, stored in pyruvic acid, the cell turns to one of the world’s most powerful electron acceptors------oxygen
Oxygen is required for the final steps of cellular respiration

3. Kreb’s Cycle Introduction
Since the Kreb’s Cycle requires oxygen, it is said to be AEROBIC
Kreb’s Cycle
Second Stage of Cellular Respiration
Takes place in the mitochondria
Process by which pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions
Also known as the Citric Acid Cycle

4. Kreb’s Cycle Steps of the Kreb’s Cycle:
1) Begins with the pyruvic acid molecules being broken down as follows
Pyruvic Acid→CO2 & Acetyl-CoA→Citric Acid
Carbon Dioxide is a waste product
2)Citric acid is then broken down into a 5-carbon compound and then into a 4 carbon compound
4-carbon compound started the process by binding with Acetyl-CoA to form Citric Acid

5. ATP and Waste Products
Every time you exhale, you release the carbon dioxide produced in the Kreb’s cycle
1 molecule of ATP is formed for every 1 cycle (net ATP in Kreb’s cycle is 2)
Cycle produces many electron carriers (NADH and FADH2) which are sent off to the electron transport chain to make the remaining ATP

8. Electron Transport Chain
3rd stage of cellular respiration
Uses NADH (Glycolysis and Kreb’s cycle) and FADH2 (Kreb’s cycle) to convert ADP into ATP
Occurs in the mitochondria

9. Electron Tranport Chain
Steps of ETC:
1) High energy electrons from NADH and FADH2 are passed along the ETC.
2) High energy electrons are removed leaving NAD+ and FAD.
3) High energy electrons pass hydrogen atoms across the membrane. These hydrogen atoms bind with oxygen to form water

10. Electron Transport Chain
Steps of ETC (cont):
4) As the hydrogen atoms escape through an ATP synthase channel, the energy from the electrons is used to bind an ADP to a phosphate to form ATP
Every NADH forms 3 ATP
Every FADH2 forms 2 ATP

13. Electron Transport Totals
10 NADH (2 from glycolysis and 8 from Kreb’s cycle) nets 30 ATP
2 FADH2 (from Kreb’s Cycle) nets 4 ATP
Total ATP in ETC=34 ATP
Water is also released during ETC

14. Efficiency of Cellular Respiration
Efficiency of respiration is 7.3 kcal/mole x 38 ATP/glucose/686 kcal/mole glucose = 40%.
The other approximately 60% is lost as heat.