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

2. Overview: Life Is Work Living cells
Require transfusions of energy from outside sources to perform their many tasks

3. The giant panda Obtains energy for its cells by eating plants
Figure 9.1

4. powers most cellular work
Energy
Flows into an ecosystem as sunlight and leaves as heat
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
Organic molecules
+ O2
ATP
powers most cellular work
Heat energy
Figure 9.2

5. Concept 1: Catabolic pathways give us energy by breaking down organic molecules

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

7. Catabolic Pathways and Production of ATP
2. Phosphorylation (adding a phosphate) of ADP creates ATP, the energy currency of the cell

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

9. Redox Reactions: Oxidation and Reduction
3. Cellular respiration occurs due to the transfer of electrons

10. The Principle of Redox
4. Redox reactions transfer electrons from one reactant to another by oxidation and reduction

11. LEO =
Lose electrons = oxidation
GER =
Gain electrons = reduction

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

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
Is glucose gaining or losing electrons?

15. The Stages of Cellular Respiration: A Preview
Respiration is a cumulative function of three metabolic stages
Glycolysis
The citric acid cycle (Krebs Cycle)
Electron Transport chain

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

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

18. Oxidative phosphorylation: electron transport and chemiosmosis
An overview of cellular respiration
Figure 9.6
Electrons
carried
via NADH
Glycolsis
Glucose
Pyruvate
ATP
Substrate-level
phosphorylation
Electrons carried
via NADH and
FADH2
Citric acid cycle
Oxidative phosphorylation: electron transport and chemiosmosis
Oxidative
Mitochondrion
Cytosol

19. Both glycolysis and the citric acid cycle
Can generate ATP by substrate-level phosphorylation
Figure 9.7
Enzyme
ATP
ADP
Product
Substrate P +

20. Concept 2: Glycolysis harvests energy by oxidizing glucose to pyruvate
1. Breaks down glucose into 2 pyruvate
2. Occurs in the
cytoplasm

21. Concept 2: Glycolysis harvests energy by oxidizing glucose to pyruvate
ATP and 2 NAD + go in

22. Energy investment phase
Products
4. 4 ATP and 2 NADH come
out
Glycolysis
Citric acid cycle
Oxidative phosphorylation
ATP
2 ATP
4 ATP
used
formed
Glucose
2 ATP + 2 P
4 ADP + 4
2 NAD+ + 4 e- + 4 H +
2 NADH
+ 2 H+
2 Pyruvate + 2 H2O
Energy investment phase
Energy payoff phase
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H +
Figure 9.8

23. Concept 3: The Krebs cycle (citric acid cycle) completes the energy-yielding oxidation of organic molecules
The Krebs cycle
takes place in the
mitochondria

24. Krebs cycle
5. Reactants: 2 pyruvate, 2 FAD, and 8 NAD+ go in
6. Products: 2 ATP, 2 FADH2, and 8 NADH come out

25. Electron transport chain Oxidative phosphorylation
Concept 4: During oxidative phosphorylation, chemiosmosis couples electron transport to make ATP
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane H+
P i
Protein complex
of electron
carners
Cyt c I II
III IV
(Carrying electrons
from, food)
NADH+
FADH2
NAD+
FAD+
2 H+ + 1/2 O2
H2O
ADP +
Electron transport chain
Electron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
Chemiosmosis
ATP synthesis powered by the flow
Of H+ back across the membrane
synthase Q
Oxidative phosphorylation
Intermembrane
space
mitochondrial
matrix
Figure 9.15

26. The Pathway of Electron Transport
Electron Transport Chain Simply Put:
1. Electrons from NADH and FADH2 donate electrons

27. The Pathway of Electron Transport
Electron Transport Chain Simply Put:
Electrons from NADH and FADH2 donate electrons
Electrons power pumps that move protons outside of membrane

28. The Pathway of Electron Transport
Electron Transport Chain Simply Put:
Electrons from NADH and FADH2 donate electrons
Electrons power pumps that move protons outside of membrane
Protons come back in membrane, powering ATP production
34 ATP made

29. The Pathway of Electron Transport
Electron Transport Chain Simply Put:
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane H+
P i
Protein complex
of electron
carners
Cyt c I II
III IV
(Carrying electrons
from, food)
NADH+
FADH2
NAD+
FAD+
2 H+ + 1/2 O2
H2O
ADP +
Electron transport chain
Electron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
Chemiosmosis
ATP synthesis powered by the flow
Of H+ back across the membrane
synthase Q
Oxidative phosphorylation
Intermembrane
space
mitochondrial
matrix
Figure 9.15

30. Chemiosmosis: The Energy-Coupling Mechanism
ATP synthase
Is the enzyme that actually makes ATP
INTERMEMBRANE SPACE H+
P i +
ADP
ATP
A rotor within the membrane spins clockwise when H+ flows past it down the H+ gradient.
A stator anchored in the membrane holds the knob stationary.
A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob.
Three catalytic sites in the stationary knob join inorganic
Phosphate to ADP to make ATP.
MITOCHONDRIAL MATRIX
Figure 9.14

31. The resulting H+ gradient
Stores energy
Drives chemiosmosis in ATP synthase
Is referred to as a proton-motive force

32. Chemiosmosis Osmosis using chemicals
H+ gradient across a membrane to powers ATP production

33. Electron transport chain Oxidative phosphorylation
Chemiosmosis and the electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane H+
P i
Protein complex
of electron
carners
Cyt c I II
III IV
(Carrying electrons
from, food)
NADH+
FADH2
NAD+
FAD+
2 H+ + 1/2 O2
H2O
ADP +
Electron transport chain
Electron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
Chemiosmosis
ATP synthesis powered by the flow
Of H+ back across the membrane
synthase Q
Oxidative phosphorylation
Intermembrane
space
mitochondrial
matrix
Figure 9.15

34. An Accounting of ATP Production by Cellular Respiration
During respiration, most energy flows in this sequence
Glucose to NADH to electron transport chain to proton-motive force to ATP

35. There are three main processes in this metabolic enterprise
Electron shuttles
span membrane
CYTOSOL
2 NADH
2 FADH2
6 NADH
Glycolysis
Glucose 2
Pyruvate
Acetyl
CoA
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
by substrate-level
phosphorylation
by oxidative phosphorylation, depending
on which shuttle transports electrons
from NADH in cytosol
Maximum per glucose:
About
36 or 38 ATP
+ 2 ATP
+ about 32 or 34 ATP or
Figure 9.16

36. About 40% of the energy in a glucose molecule
Is transferred to ATP during cellular respiration, making approximately 38 ATP

37. In the absence of oxygen
Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen
Cellular respiration
Relies on oxygen to produce ATP
In the absence of oxygen
Cells can still produce ATP through fermentation

38. Glycolysis
Can produce ATP with or without oxygen, in aerobic or anaerobic conditions
Couples with fermentation to produce ATP

39. Types of Fermentation
1. Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis

40. Fermentation
IF fermentation happens in some bacteria, alcohol is formed
IF fermentation happens in humans, lactic acid is formed

41. During lactic acid fermentation
Pyruvate is reduced directly to NADH to form lactate as a waste product

42. (a) Alcohol fermentation (b) Lactic acid fermentation
2 ADP + 2 P1
2 ATP
Glycolysis
Glucose
2 NAD+
2 NADH
2 Pyruvate
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2 Lactate
(b) Lactic acid fermentation H OH
CH3 C
O – O O–
CO2 2
Figure 9.17

43. Fermentation and Cellular Respiration Compared
Both fermentation and cellular respiration
Use glycolysis to oxidize glucose and other organic fuels to pyruvate

44. Fermentation and cellular respiration
Differ in their final electron acceptor
Cellular respiration
Produces more ATP

45. Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
Ethanol or
lactate
Acetyl CoA
MITOCHONDRION
Citric
acid
cycle
Figure 9.18

46. The Evolutionary Significance of Glycolysis
Occurs in nearly all organisms
Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

47. Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways

48. The Versatility of Catabolism
Catabolic pathways
Funnel electrons from many kinds of organic molecules into cellular respiration

49. The catabolism of various molecules from food
Amino
acids
Sugars
Glycerol
Fatty
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citric
acid
cycle
Oxidative
phosphorylation
Fats
Proteins
Carbohydrates
Figure 9.19

50. Biosynthesis (Anabolic Pathways)
The body
Uses small molecules to build other substances
These small molecules
May come directly from food or through glycolysis or the citric acid cycle

51. Regulation of Cellular Respiration via Feedback Mechanisms
Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle

52. Fructose-1,6-bisphosphate
The control of cellular respiration
Glucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
ATP
Acetyl CoA
Citric
acid
cycle
Citrate
Oxidative
phosphorylation
Stimulates
AMP + –
Figure 9.20