1. Cellular Respiration: Harvesting Chemical Energy
Chapter 9
Cellular Respiration: Harvesting Chemical Energy

2. Energy
Flows into an ecosystem as sunlight and leaves as heat

3. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic

4. One catabolic process, fermentation
Is a partial degradation of sugars that occurs without oxygen

5. Cellular respiration
Is the most prevalent and efficient catabolic pathway
Consumes oxygen and organic molecules such as glucose
Yields ATP

6. To keep working
Cells must regenerate ATP

7. The Principle of Redox Redox reactions
Transfer electrons from one reactant to another by oxidation and reduction

8. In oxidation In reduction A substance loses electrons, or is oxidized
A substance gains electrons, or is reduced

9. Examples of redox reactions
Na Cl Na Cl–
becomes oxidized (loses electron)
becomes reduced (gains electron)

10. Some redox reactions Do not completely exchange electrons
Change the degree of electron sharing in covalent bonds
CH4 H C O
Methane (reducing agent)
Oxygen (oxidizing agent)
Carbon dioxide
Water +
2O2
CO2
Energy
2 H2O
becomes oxidized
becomes reduced
Reactants
Products
Figure 9.3

11. Oxidation of Organic Fuel Molecules During Cellular Respiration
Glucose is oxidized and oxygen is reduced
C6H12O6 + 6O CO2 + 6H2O + Energy
becomes oxidized
becomes reduced

12. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
Cellular respiration
Oxidizes glucose in a series of steps

13. Oxidation of Organic Fuel Molecules During Cellular Respiration
Glucose is oxidized and oxygen is reduced
C6H12O6 + 6O CO2 + 6H2O + Energy
becomes oxidized
becomes reduced

14. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
Cellular respiration
Oxidizes glucose in a series of steps

15. Electrons from organic compounds
Are usually first transferred to NAD+, a coenzyme
NAD+ H O O– P
CH2 HO OH N+ C
NH2 N
Nicotinamide (oxidized form) +
2[H]
(from food)
Dehydrogenase
Reduction of NAD+
Oxidation of NADH
2 e– + 2 H+
2 e– + H+
NADH
Nicotinamide (reduced form)
Figure 9.4

16. NADH, the reduced form of NAD+
Passes the electrons to the electron transport chain

17. (a) Uncontrolled reaction
If electron transfer is not stepwise
A large release of energy occurs
As in the reaction of hydrogen and oxygen to form water
(a) Uncontrolled reaction
Free energy, G
H2O
Explosive release of heat and light energy
Figure 9.5 A
H2 + 1/2 O2

18. The electron transport chain
Passes electrons in a series of steps instead of in one explosive reaction
Uses the energy from the electron transfer to form ATP

20. The Stages of Cellular Respiration: A Preview
Respiration is a cumulative function of three metabolic stages
Glycolysis (does not require oxygen)
The citric acid cycle (requires oxygen)
Oxidative phosphorylation (requires oxygen)

21. Glycolysis The citric acid cycle
Breaks down glucose into two molecules of pyruvate
The citric acid cycle
Completes the breakdown of glucose

22. Oxidative phosphorylation
Is driven by the electron transport chain
Generates ATP

24. Substrate–level phosphorylation:
-Some ATP is made by direct enzymatic transfer of a phosphate group from an organic substrate to ADP.

27. ENERGY INVESTMENT PHASE
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate H OH HO
CH2OH O P
CH2O
CH2 C
CHOH
ATP
ADP
Hexokinase
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Phosphoglucoisomerase
Phosphofructokinase
Fructose-
1, 6-bisphosphate
Aldolase
Isomerase
Glycolysis 1 2 3 4 5
Oxidative
phosphorylation
Citric
acid
cycle
Figure 9.9 A
Glucose
ENERGY INVESTMENT PHASE
Glucose 6-Phosphate
Fructose 6-Phosphate
Fructose 1,6-BiPhosphate
Glyceraldehyde 3-Phosphate
DHAP

28. 1, 3-Bisphosphoglycerate
2 NAD+
NADH 2
+ 2 H+
Triose phosphate
dehydrogenase
P i P C
CHOH O
CH2 O–
1, 3-Bisphosphoglycerate
2 ADP
2 ATP
Phosphoglycerokinase
3-Phosphoglycerate
Phosphoglyceromutase
CH2OH H
2-Phosphoglycerate
2 H2O
Enolase
Phosphoenolpyruvate
Pyruvate kinase
CH3 6 8 7 9 10
Pyruvate
Figure 9.8 B
1,3-BiPhosphoglycerate
ENERGY PAYOFF PHASE
3-Phosphoglycerate
2-Phosphoglycerate
Phosphoenolpyruvate
Pyruvate

35. Why ATP variable?
Phosphphorylation and redox reactions are not directly coupled to each other, so the ratio of NADH: ATP molecules is not a whole number.
The ATP yield varies slightly depending on shuttle used to transport electrons from cytosol into mitochondrion.
Use of proton motive forces generated by redox reactions of respiration to do other works

36. Examples: Many bacteria, yeasts, humans used yeast in brewing, winemaking, and baking
Examples:certain fungi and bacteria are used to make cheese and yogurt
Human muscle cells make ATP when oxygen is scarce