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 Operates under aerobic conditions only
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 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. Coenzymes Produced in the Citric Acid Cycle
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: 2CO NADH + 1 FADH2 + GTP
Coenzymes
1 NADH
1 GTP
1 FADH2

7. Learning Check 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 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 ATP
FADH2 + 2 ADP FAD 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
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
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

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

17. ATP Energy from Pyruvate
2 pyruvate acetyl CoA + 2 CO NADH
2 pyruvate acetyl CoA + 2 CO 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 = ATP
Glucose provides two acetyl COA molecules for two turns of citric acid cycle
2 acetyl CoA ATP + 4 CO2

19. ATP from Glucose For 1 glucose molecule undergoing complete oxidation
Glycolysis ATP
2 Pyruvate to 2 Acetyl CoA 6 ATP
2 Acetyl CoA to 4 CO2 24 ATP
Glucose O CO H2O ATP