1. Cellular Respiration and Fermentation7
Cellular Respiration and Fermentation 1

2. Overview: Life Is Work
Living cells require energy from outside sources
Some animals, such as the giraffe, obtain energy by eating plants, and some animals feed on other organisms that eat plants
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3. Energy flows into an ecosystem as sunlight and leaves as heat
Photosynthesis generates O2 and organic molecules, which are used as fuel for cellular respiration
Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work
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4. Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic
Figure 7.2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
molecules
CO2 + H2O
+ O2
Cellular respiration
in mitochondria
ATP powers
most cellular work
ATP
Heat
energy

5. Concept 7.1: Catabolic pathways yield energy by oxidizing organic fuels
Several processes are central to cellular respiration and related pathways
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6. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic
Fermentation is a partial degradation of sugars that occurs without O2
Aerobic respiration consumes organic molecules and O2 and yields ATP
Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2
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7. C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat)
Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration
Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy (ATP + heat)
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8. Redox Reactions: Oxidation and Reduction
The transfer of electrons during chemical reactions releases energy stored in organic molecules
This released energy is ultimately used to synthesize ATP
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9. The Principle of Redox
Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions
In oxidation, a substance loses electrons, or is oxidized
In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)
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10. becomes oxidized (loses electron) becomes reduced (gains electron)
Figure 7.UN01
becomes oxidized
(loses electron)
becomes reduced
(gains electron)

11. becomes oxidized becomes reduced
Figure 7.UN02
becomes oxidized
becomes reduced

12. The electron donor is called the reducing agent
The electron acceptor is called the oxidizing agent
Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds
An example is the reaction between methane and O2
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13. Reactants Products becomes oxidized becomes reduced Methane (reducing
Figure 7.3
Reactants
Products
becomes oxidized
becomes reduced
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water

14. LEO says GER LEO GER Lose Electrons Oxidized Gain Electrons Reduced
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15. Redox reactions that move electrons closer to electronegative atoms, like oxygen, release chemical energy that can be put to work
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16. Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced
Organic molecules with an abundance of hydrogen, like carbohydrates and fats, are excellent fuels
As hydrogen (with its electron) is transferred to oxygen, energy is released that can be used in ATP sythesis
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17. becomes oxidized becomes reduced
Figure 7.UN03
becomes oxidized
becomes reduced

18. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
In cellular respiration, glucose and other organic molecules are broken down in a series of steps
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
Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP
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19. 2 e−+ 2 H+ 2 e− + H+ NAD+ NADH H+ Dehydrogenase Reduction of NAD+
Figure 7.4
2 e−+ 2 H+
2 e− + H+
NAD+
NADH H+
Dehydrogenase
Reduction of NAD+
+ 2[H]
(from food) + H+
Oxidation of NADH
Nicotinamide
(reduced form)
Nicotinamide
(oxidized form)

20. NADH passes the electrons to the electron transport chain
Unlike an uncontrolled reaction, the electron transport chain passes electrons in a series of steps instead of one explosive reaction
O2 pulls electrons down the chain in an energy-yielding tumble
The energy yielded is used to regenerate ATP
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21. (a) Uncontrolled reaction (b) Cellular respiration
Figure 7.5
H2 + O2
2 H + O2
Controlled
release of
energy
2 H e−
ATP
ATP
Explosive
release
Electron transport
chain
Free energy, G
Free energy, G
ATP
2 e− O2
2 H+
H2O
H2O
(a) Uncontrolled reaction
(b) Cellular respiration

22. The Stages of Cellular Respiration: A Preview
Harvesting of energy from glucose has three stages
Glycolysis (breaks down glucose into two molecules of pyruvate)
Pyruvate oxidation and the citric acid cycle (completes the breakdown of glucose)
Oxidative phosphorylation (accounts for most of the ATP synthesis)
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23. Glycolysis (color-coded teal throughout the chapter)
Figure 7.UN05 1.
Glycolysis (color-coded teal throughout the chapter) 2.
Pyruvate oxidation and the citric acid cycle
(color-coded salmon) 3.
Oxidative phosphorylation: electron transport and
chemiosmosis (color-coded violet)

24. Electrons via NADH and FADH2 Electrons via NADH Oxidative
Figure 7.6-3
Electrons
via NADH and
FADH2
Electrons
via NADH
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Pyruvate
oxidation
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
ATP
ATP
ATP
Substrate-level
Substrate-level
Oxidative

25. The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
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26. The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation
For each molecule of glucose degraded to CO2 and water by respiration, the cell makes up to 32 molecules of ATP
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27. Enzyme Enzyme ADP Substrate + ATP Product
Figure 7.7
Enzyme
Enzyme
ADP P
Substrate +
ATP
Product

28. Glycolysis occurs in the cytoplasm and has two major phases
Concept 7.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
Glycolysis (“sugar splitting”) breaks down glucose into two molecules of pyruvate
Glycolysis occurs in the cytoplasm and has two major phases
Energy investment phase
Energy payoff phase
Glycolysis occurs whether or not O2 is present
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29. Citric acid cycle Oxidative phosphorylation Pyruvate oxidation
Figure 7.UN06
Citric
acid
cycle
Oxidative
phosphorylation
Pyruvate
oxidation
Glycolysis
ATP
ATP
ATP

30. Energy Investment Phase
Figure 7.8
Energy Investment Phase
Glucose
2 ADP + 2 P
2 ATP
used
Energy Payoff Phase
4 ADP + 4 P
4 ATP
formed
2 NAD 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 e− + 4 H+
2 NADH + 2 H+

31. Glycolysis: Energy Investment Phase
Figure 7.9a
Glycolysis: Energy Investment Phase
Glyceraldehyde
3-phosphate (G3P)
ATP
Glucose
6-phosphate
Fructose
6-phosphate
ATP
Fructose
1,6-bisphosphate
Glucose
ADP
ADP
Isomerase 5
Hexokinase
Phosphogluco-
isomerase
Phospho-
fructokinase
Aldolase
Dihydroxyacetone
phosphate (DHAP) 1 4 2 3

32. 32 Glycolysis: Energy Payoff Phase Figure 7.9b 2 ATP 2 ATP 2 NADH
2 H2O
Glyceraldehyde
3-phosphate (G3P)
2 ADP
2 NAD+
+ 2 H+
2 ADP 2 2 2 2 2
Triose
phosphate
dehydrogenase
Phospho-
glycerokinase
Phospho-
glyceromutase
Enolase
Pyruvate
kinase 2 P i 9
1,3-Bisphospho-
glycerate 7
3-Phospho-
glycerate 8
2-Phospho-
glycerate
Phosphoenol-
pyruvate (PEP) 10
Pyruvate 6 32

33. Concept 7.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules
In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells), where the oxidation of glucose is completed
Before the citric acid cycle can begin, pyruvate must be converted to acetyl coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle
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34. 34 Citric acid cycle Oxidative phosphorylation Pyruvate oxidation
Figure 7.UN07
Citric
acid
cycle
Oxidative
phosphorylation
Pyruvate
oxidation
Glycolysis
ATP
ATP
ATP 34

35. Citric acid cycle Figure 7.10 Pyruvate (from glycolysis,
2 molecules per glucose)
CYTOSOL
CO2
NAD+
CoA
NADH
+ H+
Acetyl CoA
MITOCHONDRION
CoA
CoA
Citric
acid
cycle 2
CO2
FADH2
3 NAD+
FAD 3
NADH
+ 3 H+
ADP + P i
ATP

36. The citric acid cycle, also called the Krebs cycle, completes the breakdown of pyruvate to CO2
The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn
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37. 37 Citric acid cycle Oxidative phosphorylation Pyruvate oxidation
Figure 7.UN08
Citric
acid
cycle
Oxidative
phosphorylation
Pyruvate
oxidation
Glycolysis
ATP
ATP
ATP 37

38. Citric acid cycle Figure 7.11-6 Acetyl CoA 1 Oxaloacetate 8 2 Malate
CoA-SH
NADH 1
+ H+
H2O
NAD+
Oxaloacetate 8 2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle 3
NADH 7
+ H+
H2O
CO2
Fumarate
CoA-SH
α-Ketoglutarate 6 4
CoA-SH 5
FADH2
CO2
NAD+
FAD
Succinate P
NADH i
GTP
GDP
Succinyl
CoA
+ H+
ADP
ATP formation
ATP

39. 39 Start: Acetyl CoA adds its two-carbon group to
Figure 7.11a
Start: Acetyl CoA adds its
two-carbon group to
oxaloacetate, producing
citrate; this is a highly
exergonic reaction.
Acetyl CoA
CoA-SH 1
H2O
Oxaloacetate 2
Citrate
Isocitrate 39

40. Isocitrate is oxidized; NAD+ is reduced.
Figure 7.11b
Isocitrate
Redox reaction:
Isocitrate is oxidized;
NAD+ is reduced.
NAD+
NADH 3
+ H+
CO2
CO2 release
CoA-SH
α-Ketoglutarate 4
CO2 release
CO2
NAD+
Redox reaction:
After CO2 release, the resulting
four-carbon molecule is oxidized
(reducing NAD+), then made
reactive by addition of CoA.
NADH
Succinyl
CoA
+ H+

41. Succinate is oxidized; FAD is reduced.
Figure 7.11c
Fumarate 6
CoA-SH 5
FADH2
FAD
Redox reaction:
Succinate is oxidized;
FAD is reduced.
Succinate P i
Succinyl
CoA
GTP
GDP
ADP
ATP formation
ATP

42. 42 Redox reaction: Malate is oxidized; NAD+ is reduced. Oxaloacetate 8
Figure 7.11d
Redox reaction:
Malate is oxidized;
NAD+ is reduced.
NADH
+ H+
NAD+ 8
Oxaloacetate
Malate 7
H2O
Fumarate 42

43. The citric acid cycle has eight steps, each catalyzed by a specific enzyme
The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate
The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle
The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain
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