Section Outline

1. Section Outline Section 9-2 • 90% of the chemical energy that was available in glucose is still locked in the electrons of pyruvic acid • 9–2 The Krebs Cycle and Electron Transport A. The Krebs Cycle (citric acid cycle) During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions. Step 1 pyruvic acid enters the mitochondrion one carbon atom becomes part of a molecule of CO2 the two remaining carbons are joined to coenzyme A to form acetyl-CoA Acetyl-CoA adds the 2 carbon acetyl group to a 4 carbon molecule producing citric acid Go to Section:

2. Step 2 Citric acid broken down into a 4-carbon molecule, more carbon dioxide is released and electrons are transferred to energy carriers. • For each pyruvic acid an ATP is produced, 5 carrier • molecules including 4 NADH molecules are produced, and one FADH2 is produced

3. Figure 9–6 The Krebs Cycle Section 9-2 Citric Acid Production Mitochondrion Go to Section:

4. Figure 9–6 The Krebs Cycle Section 9-2 Citric Acid Production Mitochondrion Go to Section:

5. B. Electron Transport The electrons are passed from NADH and FADH2 to the electron transport chain. The electron transport chain uses the high energy electrons from the Kreb’s cycle to convert ADP into ATP. Step 1 High-energy electrons from NADH and FADH2 are passed into and along the electron transport chain The electron transport chain is composed of a series of carrier proteins that is located in the inner membrane of the mitochondrion Oxygen is the final electron acceptor. Oxygen is essential for getting rid of low-energy electrons and hydrogen ions.

6. Step 2: Every time 2 high-energy electrons transport down the electron transport chain, their energy is used to transport hydrogen ions across the membrane • Hydrogen ions build up in the intermembrane space • Step 3: The inner membranes of the mitochondria contain protein spheres called ATP synthases • As Hydrogen ions escape through channels into these proteins, the ATP synthases spin • Each time it rotates the enzyme attaches an ADP and a phosphate forming high-energy ATP • Note* Each pair of high energy electrons that moves down the electron transport chain provides enough energy to convert 3 ADP to 3 ATP molecules.

7. Figure 9–7 Electron Transport Chain Section 9-2 Electron Transport Hydrogen Ion Movement Channel Mitochondrion Intermembrane Space ATP synthase Inner Membrane Matrix ATP Production Go to Section:

8. C. The Totals Glycolysis produces just 2ATP per glucose Krebs Cycle and Electron Transport Chain produce 34 ATP These 36 ATP molecules represent about 38% of the total energy of glucose.The rest is released as heat, which is one of the reasons you body feels warmer after exercise.

9. Flowchart Section 9-2 Cellular Respiration Glucose(C6H1206) + Oxygen(02) Glycolysis KrebsCycle ElectronTransportChain Carbon Dioxide (CO2) + Water (H2O) Go to Section:

10. D. Energy and Exercise 1. Quick Energy Cells normally contain small amounts of ATP produced during glycolysis and cellular respiration The muscles of the runners contain only enough of this ATP for a few seconds of intense activity The store of ATP is used up quickly and their muscle cells are producing most of their ATP by lactic acid fermentation. To get rid of lactic acid in the muscle a chemical pathway that requires extra oxygen is used.

11. 2. Long-Term Energy Cellular respiration is the only way to generate a continuing supply of ATP because it releases energy more slowly than fermentation. The body stores energy in muscle and other tissues in the form of the carbohydrate glycogen. Enough to last for 15 to 20 minutes of activity. The body will then begin to break down other stored molecules including fats, for energy.