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

3. LE 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO2 + H2O
Organic
molecules
+ O2
Cellular respiration
in mitochondria
ATP
powers most cellular work
Heat
energy

4. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic
Fermentation is a partial degradation of sugars that occurs without oxygen
Cellular respiration consumes oxygen and organic molecules and yields ATP
Cellular Respiration Equation:

5. The Principle of Redox
Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions
Oxidation:
Reduction:

6. The electron donor is called the reducing agent
The electron receptor is called the oxidizing agent
Xe Y X Ye-
becomes oxidized (loses electron)
becomes reduced (gains electron)

7. Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water
LE 9-3
Reactants
Products
becomes oxidized
CH4 +
2 O2
CO2 +
Energy +
2 H2O
becomes reduced H H C H O O O C O H O H H
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water

8. Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced:
C6H12O6 + 6O CO2 + 6H2O + Energy
becomes oxidized
becomes reduced

9. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
Electrons from organic compounds are usually first transferred to NAD+, a coenzyme
As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration
NADH represents stored energy that is tapped to synthesize ATP

10. LE 9-4 NADH NAD+ 2 e– + 2 H+ 2 e– + H+ H+ Dehydrogenase + 2[H] + H+
(from food) + H+
Nicotinamide
(reduced form)
Nicotinamide
(oxidized form)

11. NADH passes the electrons to the electron transport chain
Oxygen pulls electrons down the chain in an energy-yielding tumble
The energy yielded is used to regenerate ATP

12. Electron transport chain+
1/2 O2
2 H +
1/2 O2
(from food via NADH)
Controlled
release of
energy for
synthesis of
ATP
2 H+ + 2 e–
ATP
Explosive
release of
heat and light
energy
ATP
Free energy, G
Free energy, G
Electron transport chain
ATP
2 e–
1/2 O2
2 H+
H2O
H2O
Uncontrolled reaction
Cellular respiration

13. The Stages of Cellular Respiration: A Preview
Cellular respiration has three stages:
Glycolysis (breaks down glucose into two molecules of pyruvate)
The citric acid cycle (completes the breakdown of glucose)
Oxidative phosphorylation (accounts for most of the ATP synthesis)
Mitochondrion
Glycolysis
Cytosol
ATP
Citric
acid
cycle
electron transport
and
chemiosmosis
NADH
NADH and
FADH2

14. LE 9-6_1 Glycolysis Glucose Pyruvate Cytosol Mitochondrion ATP
Substrate-level
phosphorylation

15. LE 9-6_2 Glycolysis Citric acid cycle Glucose Pyruvate Cytosol
Mitochondrion
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation

16. LE 9-6_3 Mitochondrion Glycolysis Pyruvate Glucose Cytosol ATP
Substrate-level
phosphorylation
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2

17. Animation: Cell Respiration Overview

18. Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
Enzyme
ADP P
Substrate
Product
ATP +

19. Animation: Glycolysis
Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate
Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate
Glycolysis occurs in the cytoplasm and has two major phases:
Energy investment phase
Energy payoff phase
Animation: Glycolysis

20. LE 9-8 Energy investment phase Glucose 2 ADP + 2 P 2 ATP used
Glycolysis
Citric
acid
cycle
Oxidative
phosphorylation
Energy payoff phase
ATP
ATP
ATP
4 ADP + 4 P
4 ATP
formed
2 NAD+ + 4 e– + 4 H+
2 NADH
+ 2 H+
2 Pyruvate + 2 H2O
Net
Glucose
2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used
2 ATP
2 NAD+ + 4 e– + 4 H+
2 NADH + 2 H+

21. LE 9-9a_1 Glucose ATP Hexokinase ADP Glucose-6-phosphate Glycolysis
Citric
acid
cycle
phosphorylation
Oxidation
Glucose
ATP
ATP
ATP
ATP
Hexokinase
ADP
Glucose-6-phosphate

22. LE 9-9a_2 Glucose ATP Hexokinase ADP Glucose-6-phosphate
Glycolysis
Citric
acid
cycle
Oxidation
phosphorylation
Glucose
ATP
ATP
ATP
ATP
Hexokinase
ADP
Glucose-6-phosphate
Phosphoglucoisomerase
Fructose-6-phosphate
ATP
Phosphofructokinase
ADP
Fructose-
1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate

23. LE 9-9b_1 2 NAD+ Triose phosphate dehydrogenase 2 NADH + 2 H+
1, 3-Bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
2-Phosphoglycerate

24. LE 9-9b_2 2 NAD+ Triose phosphate dehydrogenase 2 NADH + 2 H+
1, 3-Bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
2-Phosphoglycerate
Enolase
2 H2O
Phosphoenolpyruvate
2 ADP
Pyruvate kinase
2 ATP
Pyruvate

25. Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules
Before the citric acid cycle can begin, pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis
CYTOSOL
Pyruvate
NAD+
MITOCHONDRION
Transport protein
NADH
+ H+
Coenzyme A
CO2
Acetyl Co A

26. Animation: Electron Transport
The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix
Pyruvate
(from glycolysis,
2 molecules per glucose)
ATP
Glycolysis
Oxidation
phosphorylation
Citric
acid
cycle
NAD+
NADH
+ H+
CO2
CoA
Acetyl CoA 2
3 NAD+
+ 3 H+ 3
ADP + P i
FADH2
FAD
Animation: Electron Transport

27. acetyl CoA + oxaloacetate citrate
The citric acid cycle has eight steps, each catalyzed by a specific enzyme
acetyl CoA + oxaloacetate citrate
The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle
Electron Carriers:
NADH and FADH2

28. LE 9-12_1 Acetyl CoA H2O Oxaloacetate Citrate Isocitrate Citric acid
Glycolysis
Citric
acid
cycle
Oxidation
phosphorylation
ATP
ATP
ATP
Acetyl CoA
H2O
Oxaloacetate
Citrate
Isocitrate
Citric
acid
cycle

29. LE 9-12_2 Acetyl CoA H2O Oxaloacetate Citrate Isocitrate CO2 Citric
Glycolysis
Citric
acid
cycle
Oxidation
phosphorylation
ATP
ATP
ATP
Acetyl CoA
H2O
Oxaloacetate
Citrate
Isocitrate
CO2
Citric
acid
cycle
NAD+
NADH
+ H+
a-Ketoglutarate
CO2
NAD+
NADH
Succinyl
CoA
+ H+

30. LE 9-12_3 Acetyl CoA H2O Oxaloacetate Citrate Isocitrate CO2 Citric
Glycolysis
Citric
acid
cycle
Oxidation
phosphorylation
ATP
ATP
ATP
Acetyl CoA
H2O
Oxaloacetate
Citrate
Isocitrate
CO2
Citric
acid
cycle
NAD+
NADH
Fumarate
+ H+
a-Ketoglutarate
FADH2
CO2
NAD+
FAD
Succinate P
NADH i
GTP
GDP
Succinyl
CoA
+ H+
ADP
ATP

31. LE 9-12_4 Acetyl CoA NADH + H+ H2O NAD+ Oxaloacetate Malate Citrate
Glycolysis
Citric
acid
cycle
Oxidation
phosphorylation
ATP
ATP
ATP
Acetyl CoA
NADH
+ H+
H2O
NAD+
Oxaloacetate
Malate
Citrate
Isocitrate
CO2
Citric
acid
cycle
NAD+
H2O
NADH
Fumarate
+ H+
a-Ketoglutarate
FADH2
CO2
NAD+
FAD
Succinate P
NADH i
GTP
GDP
Succinyl
CoA
+ H+
ADP
ATP

32. Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food
These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

33. The Pathway of Electron Transport
The electron transport chain is in the cristae of the mitochondrion
Most of the chain’s components are proteins
Electrons drop in free energy as they go down the chain and are finally passed to O2, forming water

34. LE 9-13 NADH 50 FADH2 Multiprotein complexes 40 I FMN FAD Fe•S Fe•S IIQ
III
Cyt b
Oxidative
phosphorylation:
electron transport
and chemiosmosis
Glycolysis
Citric
acid
cycle
Fe•S 30
Cyt c1
Free energy (G) relative to O2 (kcal/mol) IV
Cyt c
Cyt a
ATP
ATP
ATP
Cyt a3 20 10
2 H+ + 1/2 O2
H2O

35. Chemiosmosis: The Energy-Coupling Mechanism
Electron transfer in the ETC causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
H+ then moves back across the membrane, passing through channels in ATP synthase
This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work

36. LE 9-15 Inner mitochondrial membrane H+ H+ H+ H+ Protein complex
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and chemiosmosis
Glycolysis
ATP
ATP
ATP H+ H+ H+ H+
Protein complex
of electron
carriers
Cyt c
Intermembrane
space Q IV I
III
ATP
synthase
Inner
mitochondrial
membrane II
2H+ + 1/2 O2
H2O
FADH2
FAD
NADH
+ H+
NAD+
ADP + P
ATP i
(carrying electrons
from food) H+
Mitochondrial
matrix
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
Oxidative phosphorylation

37. LE 9-14
INTERMEMBRANE SPACE H+
ATP
MITOCHONDRAL MATRIX
ADP + P i
A rotor within the membrane spins as shown when H+ flows past
it down the H+ gradient.
A stator anchored in the membrane holds the knob stationary.
A rod (or “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.
The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work

38. An Accounting of ATP Production by Cellular Respiration
During cellular respiration, most energy flows in this sequence:
glucose NADH electron transport chain proton-motive force ATP
About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP

39. LE 9-16 CYTOSOL Electron shuttles span membrane MITOCHONDRION 2 NADHor
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Glycolysis
Oxidative
phosphorylation:
electron transport
and
chemiosmosis 2
Pyruvate 2
Acetyl
CoA
Citric
acid
cycle
Glucose
+ 2 ATP
+ 2 ATP
+ about 32 or 34 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
by oxidation phosphorylation, depending
on which shuttle transports electrons
form NADH in cytosol
About
36 or 38 ATP
Maximum per glucose:

40. Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen
Cellular respiration requires O2 to produce ATP
Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
In the absence of O2, glycolysis couples with fermentation to produce ATP

41. Types of Fermentation
Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis
Two common types are alcohol fermentation and lactic acid fermentation

42. In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2
Alcohol fermentation by yeast is used in brewing, winemaking, and baking
Play

43. Alcohol fermentation CO2 + 2 H+ 2 NADH 2 NAD+ 2 Acetaldehyde 2 ATP
LE 9-17a
CO2
+ 2 H+
2 NADH
2 NAD+
2 Acetaldehyde
2 ATP
2 ADP + 2 P i
2 Pyruvate 2
2 Ethanol
Alcohol fermentation
Glucose
Glycolysis

44. In lactic acid fermentation, pyruvate is reduced by NADH, forming lactate as an end product, with no release of CO2
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt
Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce

45. Lactic acid fermentation
LE 9-17b
2 ADP + 2 P
2 ATP i
Glucose
Glycolysis
2 NAD+
2 NADH 2
CO2
+ 2 H+
2 Pyruvate
2 Lactate
Lactic acid fermentation

46. Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration
Pyruvate
Glucose
CYTOSOL
No O2 present
Fermentation
Ethanol or
lactate
Acetyl CoA
MITOCHONDRION
O2 present
Cellular respiration
Citric
acid
cycle

47. The Versatility of Catabolism
Citric
acid
cycle
Oxidative
phosphorylation
Proteins
NH3
Amino
acids
Sugars
Carbohydrates
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
Fatty
Glycerol
Fats
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration