Metabolism and Energy Production

1. Metabolism and Energy Production Citric Acid Cycle Electron Transport Chain ATP Energy from Glucose Oxidation of Fatty Acids Metabolic Pathways for Amino Acids

2. Citric Acid Cycle A reaction series that • Operates under aerobic conditions only • Oxidizes the 2 carbon atoms of acetyl CoA to CO2 • Provides reduced coenzymes O || CH3–C –CoA 2 CO2 , FADH2, 3 NADH, + ATP acetyl CoA

3. Steps 1-3 in Citric Acid Cycle α-ketoglutarate

4. Steps 4-5 of citric acid cycle In the next reactions, α-ketoglutarate is oxidized to succinate. α-ketoglutarate succinate

5. Steps 6-8 of citric acid cycle More oxidations convert succinate to oxaloacetate. The C=C requires FAD.

6. 1. Acetyl CoA (2C) + oxaloacetate (4C) to citrate (6C) Citrate (6C) to α-ketoglutarate (5C) + CO2 3. α-ketoglutarate (5C) to succinate (4C) + CO2. GDP picks up Pi. Succinate(4C) to fumarate (C=C) to malate Malate to oxaloacetate. Start again. Total: 2CO2 + 3 NADH + 1 FADH2 + GTP Coenzymes 1 NADH 1 NADH 1 GTP 1 FADH2 1 NADH Coenzymes Produced in the Citric Acid Cycle

7. Learning Check E1 Complete the following statements: • When 1 acetyl CoA enters the citric acid cycle, the C atoms produce ____CO2. • In 1 cycle, a total of ____NADH are produced. • In 1 cycle, a total of ____FADH2 are produced.

8. Solution E1 Complete the following statements: • When 1 acetyl CoA enters the citric acid cycle, the C atoms produce 2 CO2. • In 1 cycle, a total of 3 NADH are produced. • In 1 cycle, a total of 1 FADH2 are produced.

9. Regulation of Citric Acid Cycle • Operates when ATP is needed • High levels of ATP and/or NADH inhibit citrate synthetase (first step in cycle) • High levels of ADP and NAD+ activate isocitrate dehydrogenase • Low levels of ATP or high levels of acetyl CoA speed up the cycle to give energy ATP

10. Electron Transport Chain • A series of electron carriers • Transfers H+ and electrons from coenzymes NADH and FADH2 (citric acid cycle) • Energy released along chain to make ATP NADH + 3 ADP NAD+ + 3 ATP FADH2 + 2 ADP FAD + 2 ATP

11. Electron Carriers • Found in three protein complexes • Attached to inner membrane of mitochondria • H+ move into intermembrane space to create proton gradient • As H+ return to matrix, ATP synthase uses energy to synthesize ATP • Oxidation phosphorylation ADP + Pi + Energy ATP

12. Enzyme Complexes • NADH dehydrogenase • Cytochrome c reductase 3. Cytochrome c Oxidase Coenzyme A Cytochrome c

13. Chemiosmotic Model Intermembrane space H+ H+ H+ H+ H+ H+ e- NADH + H+ FADH2 H2O Matrix ADP + P ATP Cytc Q

14. Learning Check E2 Classify each as (1) a product of the citric acid cycle, (2) a product of the electron transport chain A. CO2 B. FADH2 C. NAD+ D. NADH E. ATP

15. Solution E2 Classify each as (1) a product of the citric acid cycle, (2) a product of the electron transport chain A. 1 CO2 B. 1 FADH2 C. 2 NAD+ D. 1 NADH E. 2 ATP

16. ATP Energy from Glycolysis(Aerobic) • In the electron transport system NADH = 3 ATP FADH2 = 2 ATP • Glycolysis Glucose 2 pyruvate + 2 ATP + 2 NADH NADH in cytoplasm FADH2 mitochondria Glucose 2 pyruvate + 6 ATP

17. ATP Energy from Pyruvate 2 pyruvate 2 acetyl CoA + 2 CO2 + 2 NADH 2 pyruvate 2 acetyl CoA + 2 CO2 + 6 ATP

18. ATP Energy from Citric Acid Cycle One turn of the citric acid cycle 3 NADH x 3 ATP = 9 ATP 1 FADH2 x 2 ATP = 2 ATP 1 GTP x 1 ATP = 1 ATP Total = 12 ATP Glucose provides two acetyl COA molecules for two turns of citric acid cycle 2 acetyl CoA 24 ATP + 4 CO2

19. ATP from Glucose For 1 glucose molecule undergoing complete oxidation Glycolysis 6 ATP 2 Pyruvate to 2 Acetyl CoA 6 ATP 2 Acetyl CoA to 4 CO224 ATP Glucose + 6 O2 6 CO2 + 6 H2O + 36 ATP