1. Cellular Respiration and Fermentation7
Cellular Respiration and Fermentation

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. 3) Cellular respiration
Figure 7.2
1) Light
Energy Enters
ECOSYSTEM
2) Photosynthesis
in chloroplasts
Organic
molecules
CO2  H2O
 O2
3) Cellular respiration
in mitochondria
Figure 7.2 Energy flow and chemical recycling in ecosystems
4) ATP powers
most cellular work
ATP
5) Heat
Energy Lost 3

4. 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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5. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic
Energy is released
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6. 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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7. 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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8. The Principle of Redox
Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions
Redox reactions that move electrons closer to electronegative atoms, like oxygen, release chemical energy that can be put to work
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9. becomes oxidized becomes reduced
Figure 7.UN02
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)
becomes oxidized
Figure 7.UN02 In-text figure, generalized redox reaction, p. 136
becomes reduced 9

10. The electron donor is called the reducing agent
The electron acceptor is called the oxidizing agent
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11. 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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12. becomes oxidized becomes reduced
Figure 7.UN03
becomes oxidized
becomes reduced
Figure 7.UN03 In-text figure, cellular respiration redox reaction, p. 137 12

13. 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
Each NADH (the reduced form of NAD) represents stored energy that is tapped to synthesize ATP
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14. 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)
Figure 7.4 NAD+ as an electron shuttle 14

15. NADH passes the electrons to the electron transport chain
The energy yielded is used to regenerate ATP
But not all at once.
WHY??????????
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16. (a) Uncontrolled reaction (b) Cellular respiration
Figure 7.5
H2  O2
2 H  O2
Controlled
release of
energy
2 H  2 e−
ATP
ATP
Electron transport
chain
Free energy, G
Free energy, G
Explosive
release
ATP
2 e−
Figure 7.5 An introduction to electron transport chains O2
2 H
H2O
H2O
(a) Uncontrolled reaction
(b) Cellular respiration 16

17. 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 (aka Krebs Cycle) completes breakdown of glucose
Oxidative phosphorylation (accounts for most of the ATP synthesis)
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18. 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)
Figure 7.UN05 In-text figure, color code for stages of cellular respiration, p. 139 18

19. 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
Figure An overview of cellular respiration (step 3)
ATP
ATP
ATP
Substrate-level
Substrate-level
Oxidative 19

20. For each molecule of glucose degraded the cell makes up to 32 molecules of ATP
The process that generates most (almost 90%) of the ATP is called oxidative phosphorylation because it is dependent on oxygen
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21. Figure 7.7
Enzyme
Enzyme
ADP P
Substrate 
ATP
Figure 7.7 Substrate-level phosphorylation
Product
A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation 21

22. 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 whether or not O2 is present 22

23. 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  4 e−  4 H
2 NADH
 2 H
Figure 7.8 The energy input and output of glycolysis
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 23

24. 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
Figure 7.9a A closer look at glycolysis (part 1: investment phase) 24

25. Glycolysis: Energy Payoff Phase
Figure 7.9b
Glycolysis: Energy Payoff Phase
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
Figure 7.9b A closer look at glycolysis (part 2: payoff phase) 25

26. 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  4 e−  4 H
2 NADH
 2 H
Figure 7.8 The energy input and output of glycolysis
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 26

27. Which statement about glycolysis is true?
It splits water.
It occurs in the mitichondria.
It occurs in the cytoplasm.
It makes the most ATP compared to the two other steps.
It splits lipids.

28. What is the NET amount of ATP produced by glycolysis?

29. 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
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30. Figure 7.UN07
Figure 7.UN07 In-text figure, mini-map, pyruvate oxidation, p. 142
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 30

31. 2 molecules per glucose) CYTOSOL
Figure 7.10a
Pyruvate
(from glycolysis,
2 molecules per glucose)
CYTOSOL
CO2
NAD
CoA
Figure 7.10a An overview of pyruvate oxidation and the citric acid cycle (part 1: pyruvate oxidation)
NADH
 H
Acetyl CoA
MITOCHONDRION
CoA 31

32. For each Acetyl CoA
Figure 7.10b An overview of pyruvate oxidation and the citric acid cycle (part 2: citric acid cycle)
The citric acid cycle, also called the Krebs cycle, completes the breakdown of pyruvate to CO2 32

33. Start: Acetyl CoA adds its two-carbon group to oxaloacetate, producing
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
Figure 7.11a A closer look at the citric acid cycle (part 1) 2
Citrate
Isocitrate 33

34. 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
-Ketoglutarate 4
Figure 7.11b A closer look at the citric acid cycle (part 2)
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 34

35. 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
GTP
GDP
Succinyl
CoA
Figure 7.11c A closer look at the citric acid cycle (part 3)
ADP
ATP formation
ATP 35

36. 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
Figure 7.11d A closer look at the citric acid cycle (part 4)
H2O
Fumarate 36

37. The citric acid cycle has eight steps, each catalyzed by a specific enzyme (last parts regenerate the Oxaloacetate)
Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food
These are shuttled to the ECM
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38. x 2 Citric acid cycle Acetyl CoA CoA CoA 2 CO2 FADH2 3 NAD 3 NADH FAD
Figure 7.10b An overview of pyruvate oxidation and the citric acid cycle (part 2: citric acid cycle) 3
NADH
FAD
 3 H
ADP  P i
ATP 38

39. How many CO2 molecules are generated per acetyl CoA molecule entering the citric acid cycle?
one
two
four
six

40. Concept 7.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
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41. The Pathway of Electron Transport
The electron transport chain is in the inner membrane (cristae) of the mitochondrion
Most of the chain’s components are proteins, which exist in multiprotein complexes
Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O
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42. Oxidative phosphorylation: electron transport and chemiosmosis Citric
Figure 7.UN09
Oxidative
phosphorylation:
electron transport
and chemiosmosis
Citric
acid
cycle
Pyruvate
oxidation
Glycolysis
Figure 7.UN09 In-text figure, mini-map, oxidative phosphorylation, p. 144
ATP
ATP
ATP 42

43. Free energy (G) relative to O2 (kcal/mol)
Carriers accept and donate electrons
Electrons lose free energy along the chain and are passed to O2, forming H2O
NADH 50 2 e−
NAD
FADH2
Multiprotein
complexes 2 e−
FAD 40 I
FMN II
Fe•S
Fe•S Q
III
Cyt b 30
Fe•S
Cyt c1 IV
Cyt c
Free energy (G) relative to O2 (kcal/mol)
Cyt a
Cyt a3 20
Figure 7.12 Free-energy change during electron transport 10 2 e−
(originally from
NADH or FADH2)
2 H  ½ O2
H2O 43

44. The electron transport chain generates no ATP directly
It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts
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45. Chemiosmosis: The Energy-Coupling Mechanism
Electron transfer in the electron transport chain causes proteins to pump H from the mitochondrial matrix to the intermembrane space
Makes a gradient
H then moves back across the membrane, passing through the protein complex, ATP synthase
Does work
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46. Electron transport chain Oxidative phosphorylation
Figure 7.14 H H
Protein
complex
of electron
carriers H H
Cyt c IV Q
III I
ATP
synthase II
2 H  ½ O2
H2O
FADH2
FAD
NADH
NAD
ADP  P
ATP i
(carrying electrons
from food) H
Figure 7.14 Chemiosmosis couples the electron transport chain to ATP synthesis 1
Electron transport chain 2
Chemiosmosis
Oxidative phosphorylation
ATP synthase uses the exergonic flow of H to drive phosphorylation of ATP
This is an example of chemiosmosis 46

47. H INTERMEMBRANE SPACE Stator Rotor Internal rod Catalytic knob ADP 
Figure 7.13 H
INTERMEMBRANE SPACE
Stator
Rotor
Internal rod
Catalytic knob
Figure 7.13 ATP synthase, a molecular mill
ADP  P
ATP
MITOCHONDRIAL MATRIX i 47

48. The energy stored in a H gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis
The H gradient is referred to as a proton-motive force, emphasizing its capacity to do work
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49. What drives chemiosmosis?
H+ gradient
ATP
NADH and FADH2
NaCl transport

50. An Accounting of ATP Production by Cellular Respiration
During cellular respiration, most energy flows in the following sequence:
glucose  NADH  electron transport chain  proton-motive force  ATP
There are several reasons why the number of ATP molecules is not known exactly
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51. Figure 7.15
Electron shuttles
span membrane
MITOCHONDRION
2 NADH
CYTOSOL or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Glycolysis
Pyruvate
oxidation
2 Acetyl CoA
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Citric
acid
cycle 2
Pyruvate
Glucose
 2 ATP
Figure 7.15 ATP yield per molecule of glucose at each stage of cellular respiration
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
Maximum per glucose:
About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP 51

52. The figure to the right represents an overview of the different processes of cellular respiration. Which of the following correctly identifies the order of the different processes?
1. Glycolysis, 2. electron transport chain, 3. citric acid cycle
1. Glycolysis, 2. citric acid cycle, 3. electron transport chain
1. Citric acid cycle, 2. electron transport chain, 3. glycolysis
1. Electron transport chain, 2. glycolysis, 3. citric acid cycle

53. Concept 7.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen
Most cellular respiration requires O2 to produce ATP
Without O2, the electron transport chain will cease to operate
What if there is no O2 available??????
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54. Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example, sulfate
Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP
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55. 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
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56. (a) Alcohol fermentation (pyruvate converted to ethanol)
Figure 7.16a
2 ADP  2 P
2 ATP i
Glucose
Glycolysis
2 Pyruvate
2 NAD
2 NADH 2
CO2
 2 H
Figure 7.16a Fermentation (part 1: alcohol)
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation (pyruvate converted to ethanol) 56

57. Alcohol fermentation by yeast is used in brewing, winemaking, and baking
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58. (b) Lactic acid fermentation (pyruvate converted to Lactate)
Figure 7.16b
2 ADP  2 P
2 ATP i
Glucose
Glycolysis
2 NAD
2 NADH
 2 H
2 Pyruvate
Figure 7.16b Fermentation (part 2: lactic acid)
2 Lactate
(b) Lactic acid fermentation (pyruvate converted to Lactate) 58

59. Lactic acid fermentation by some fungi and bacteria is used to make cheese, yogurt, and some pickles
Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce
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60. Comparing Fermentation with Anaerobic and Aerobic Respiration
All use glycolysis (net ATP  2) to oxidize glucose and harvest chemical energy of food
In all three, NAD is the oxidizing agent that accepts electrons during glycolysis
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61. Obligate anaerobes carry out only fermentation or anaerobic respiration
Yeast and many bacteria are facultative anaerobes, can survive using either fermentation or cellular respiration
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62. Cellular respiration produces 32 ATP per glucose molecule
Figure 7.17 Pyruvate as a key juncture in catabolism
Cellular respiration produces 32 ATP per glucose molecule
Fermentation produces 2 ATP per glucose molecule 62

63. The final electron acceptor in the electron transport chain is
NAD+
FAD+
H2O
oxygen

64. The Evolutionary Significance of Glycolysis
Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere
Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate ATP
Glycolysis is a very ancient process
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65. Concept 7.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways
Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways
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66. The Versatility of Catabolism
Catabolic pathways funnel electrons from many kinds of organic molecules (not just Glucose) into cellular respiration
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67. Fats are digested to glycerol (used in glycolysis) and fatty acids
Fatty acids are broken down by beta oxidation and yield acetyl CoA
An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate
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68. Amino acids Fatty acids Citric acid cycle Oxidative phosphorylation
Figure
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
Glycolysis
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Figure The catabolism of various molecules from food (step 5)
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation 68