1. Cellular Respiration and Fermentation7
Cellular Respiration and Fermentation

2. Concept 7.4: 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
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3. The Pathway of Electron Transport
The electron transport chain is located in the inner membrane (cristae) of the mitochondrion
Most of the chain’s components are proteins, which exist in multiprotein complexes
The carriers alternate reduced and oxidized states as they accept and donate electrons
Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O
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4. The electron transport chain generates no ATP directly
Electrons are transferred from NADH or FADH2 to the electron transport chain
Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2
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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5. CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE
Figure 7.UN09
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYL-
ATION
PYRUVATE
OXIDATION
GLYCOLYSIS
Figure 7.UN09 In-text figure, mini-map, oxidative phosphorylation, p. 150
ATP
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6. (least electronegative)
Figure 7.12
NADH
(least electronegative) 50 2 e-
NAD+
FADH2
Free energy (G) relative to O2 (kcal/mol)
Complexes I-IV 2 e-
FAD 40 I
FMN II
Fe•S
Fe•S Q
III
Cyt b 30
Fe•S
Cyt c1 IV
Cyt c
Cyt a
Electron transport
chain
Cyt a3 20
Figure 7.12 Free-energy change during electron transport 10 2 e-
2 H+ + ½ O2
(most electronegative)
H2O
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7. (least electronegative)
Figure
NADH
(least electronegative) 50 2 e-
Free energy (G) relative to O2 (kcal/mol)
NAD+
FADH2
Complexes I-IV 2 e-
FAD I 40
FMN II
Fe•S
Fe•S Q
III
Cyt b
Fe•S 30
Cyt c1 IV
Cyt c
Figure Free-energy change during electron transport (part 1)
Cyt a
Electron transport
chain
Cyt a3 20 e- 10 2
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8. Free energy (G) relative to O2 (kcal/mol) 30
Figure
Free energy (G) relative to O2 (kcal/mol)
Fe•S 30
Cyt c1 IV
Cyt c
Electron transport
chain
Cyt a
Cyt a3 20 e- 10 2
Figure Free-energy change during electron transport (part 2)
2 H+ + ½ O2
(most electronegative)
H2O
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9. 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
H then moves back across the membrane, passing through the protein complex, ATP synthase
ATP synthase uses the exergonic flow of H to drive phosphorylation of ATP
This is an example of chemiosmosis, the use of energy in a H gradient to drive cellular work
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10. Video: ATP Synthase 3-D Side View
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11. Video: ATP Synthase 3-D Top View
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12. (a) The ATP synthase protein complex
Figure 7.13
Intermembrane
space
Inner
mitochondrial
membrane
Mitochondrial
matrix
INTERMEMBRANE
SPACE H+
Stator
Rotor
Internal
rod
Figure 7.13 ATP synthase, a molecular mill
Catalytic
knob
ADP + P
ATP i
MITOCHONDRIAL MATRIX
(a) The ATP synthase protein complex
(b) Computer model of ATP synthase
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13. (a) The ATP synthase protein complex
Figure H+
INTERMEMBRANE SPACE
Stator
Rotor
Internal rod
Catalytic knob
Figure ATP synthase, a molecular mill (part 1: )
ADP +
MITOCHONDRIAL MATRIX P
ATP i
(a) The ATP synthase protein complex
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14. (b) Computer model of ATP synthase
Figure
Figure ATP synthase, a molecular mill (part 2: )
(b) Computer model of ATP synthase
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15. 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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16. CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE
Figure 7.UN09
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYL-
ATION
PYRUVATE
OXIDATION
GLYCOLYSIS
Figure 7.UN09 In-text figure, mini-map, oxidative phosphorylation, p. 150
ATP
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17. Electron transport chain Chemiosmosis
Figure 7.14 H+
ATP
synthase H+ H+ H+
Protein complex
of electron
carriers
Cyt c IV Q
III I II
2 H+ + ½ O2
H2O
FADH2
FAD
NADH
NAD+
Figure 7.14 Chemiosmosis couples the electron transport chain to ATP synthesis
ADP + P
ATP i
(carrying electrons
from food) H+
Electron transport chain
Chemiosmosis
Oxidative phosphorylation
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18. Electron transport chain
Figure H+ H+ H+
Cyt c
Protein complex
of electron
carriers IV Q
III I II
2 H+ + ½ O2
H2O
FADH2
FAD
Figure Chemiosmosis couples the electron transport chain to ATP synthesis (part 1: electron transport chain)
NADH
NAD+
(carrying electrons
from food)
Electron transport chain
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19. ATP synthase ATP Chemiosmosis H+ ADP + P H+ i Figure 7.14-2
Figure Chemiosmosis couples the electron transport chain to ATP synthesis (part 2: chemiosmosis)
ADP + P
ATP i H+
Chemiosmosis
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20. 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
About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP
There are several reasons why the number of ATP molecules is not known exactly
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21. OXIDATIVE PHOSPHORYLATION CITRIC ACID CYCLE
Figure 7.15
CYTOSOL
Electron shuttles
span membrane
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
GLYCOLYSIS
PYRUVATE OXIDATION
OXIDATIVE
PHOSPHORYLATION
CITRIC
ACID
CYCLE
Glucose
2 Pyruvate
2 Acetyl CoA
(Electron transport
and chemiosmosis)
Figure 7.15 ATP yield per molecule of glucose at each stage of cellular respiration
+ 2 ATP
+ 2 ATP
+ about 26 or 28 ATP
About
Maximum per glucose:
30 or 32 ATP
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22. Electron shuttles span membrane GLYCOLYSIS Glucose 2 Pyruvate 2 NADH
Figure
Electron shuttles
span membrane
2 NADH or
2 FADH2
2 NADH
GLYCOLYSIS
Glucose
2 Pyruvate
Figure ATP yield per molecule of glucose at each stage of cellular respiration (part 1: glycolysis)
+ 2 ATP
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23. PYRUVATE OXIDATION CITRIC ACID CYCLE 2 Acetyl CoA 2 NADH 6 NADH
Figure
2 NADH
6 NADH
2 FADH2
PYRUVATE OXIDATION
CITRIC
ACID
CYCLE
2 Acetyl CoA
Figure ATP yield per molecule of glucose at each stage of cellular respiration (part 2: citric acid cycle)
+ 2 ATP
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24. OXIDATIVE PHOSPHORYLATION
Figure
2 NADH or
2 FADH2
2 NADH
6 NADH
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron transport
and chemiosmosis)
Figure ATP yield per molecule of glucose at each stage of cellular respiration (part 3: oxidative phosphorylation)
+ about 26 or 28 ATP
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25. About Maximum per glucose: 30 or 32 ATP Figure 7.15-4
Figure ATP yield per molecule of glucose at each stage of cellular respiration (part 4: maximum ATP yield per glucose)
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26. 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
In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP
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27. 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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28. 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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29. In alcohol fermentation, pyruvate is converted to ethanol in two steps
The first step releases CO2 from pyruvate, and the second step reduces the resulting acetaldehyde to ethanol
Alcohol fermentation by yeast is used in brewing, winemaking, and baking
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30. Animation: Fermentation Overview
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31. (a) Alcohol fermentation
Figure
2 ADP + 2 P 2
ATP i
Glucose
GLYCOLYSIS
2 Pyruvate 2
NAD+ 2
NADH
2 CO2
+ 2 H+
Figure Fermentation (part 1: alcohol)
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
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32. 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
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33. (b) Lactic acid fermentation
Figure
2 ADP + 2 P 2
ATP i
Glucose
GLYCOLYSIS 2
NAD+ 2
NADH
+ 2 H+
2 Pyruvate
Figure Fermentation (part 2: lactic acid)
2 Lactate
(b) Lactic acid fermentation
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34. (a) Alcohol fermentation (b) Lactic acid fermentation
Figure 7.16
2 ADP + 2 P 2
ATP i
2 ADP + 2 P 2
ATP i
Glucose
GLYCOLYSIS
Glucose
GLYCOLYSIS
2 Pyruvate 2
NAD+ 2
NADH
2 CO2 2
NAD+ 2
NADH
+ 2 H+
+ 2 H+
2 Pyruvate
Figure 7.16 Fermentation
2 Ethanol
2 Acetaldehyde
2 Lactate
(a) Alcohol fermentation
(b) Lactic acid fermentation
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35. Comparing Fermentation with Anaerobic and Aerobic Respiration
All use glycolysis (net ATP = 2) to oxidize glucose and other organic fuels to pyruvate
In all three, NAD+ is the oxidizing agent that accepts electrons from food during glycolysis
The mechanism of NADH oxidation differs
In fermentation the final electron acceptor is an organic molecule such as pyruvate or acetaldehyde
Cellular respiration transfers electrons from NADH to a carrier molecule in the electron transport chain
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36. Cellular respiration produces about 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule
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37. Obligate anaerobes carry out only fermentation or anaerobic respiration and cannot survive in the presence of O2
Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration
In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes
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38. Ethanol, lactate, or other products CITRIC ACID CYCLE
Figure 7.17
Glucose
Glycolysis
CYTOSOL
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol,
lactate, or
other products
Acetyl CoA
Figure 7.17 Pyruvate as a key juncture in catabolism
CITRIC
ACID
CYCLE
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39. The Evolutionary Significance of Glycolysis
Glycolysis is the most common metabolic pathway among organisms on Earth, indicating that it evolved early in the history of life
Early prokaryotes may have generated ATP exclusively through glycolysis due to the low oxygen content in the atmosphere
The location of glycolysis in the cytosol also indicates its ancient origins; eukaryotic cells with mitochondria evolved much later than prokaryotic cells
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40. Concept 7.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways
Glycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways
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41. The Versatility of Catabolism
Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration
Glycolysis accepts a wide range of carbohydrates
Proteins must be digested to amino acids and amino groups must be removed before amino acids can feed glycolysis or the citric acid cycle
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42. 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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43. Proteins Carbohydrates Fats Amino acids Sugars Glycerol acids
Figure 7.18-s1
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
Figure 7.18-s1 The catabolism of various molecules from food (step 1)
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44. Proteins Carbohydrates Fats Amino acids Sugars Glycerol acids
Figure 7.18-s2
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
GLYCOLYSIS
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Figure 7.18-s2 The catabolism of various molecules from food (step 2)
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45. Proteins Carbohydrates Fats Amino acids Sugars Glycerol acids
Figure 7.18-s3
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
GLYCOLYSIS
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Figure 7.18-s3 The catabolism of various molecules from food (step 3)
Acetyl CoA
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46. Amino acids CITRIC ACID CYCLE
Figure 7.18-s4
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
GLYCOLYSIS
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Figure 7.18-s4 The catabolism of various molecules from food (step 4)
Acetyl CoA
CITRIC
ACID
CYCLE
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47. Amino acids CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION
Figure 7.18-s5
Proteins
Carbohydrates
Fats
Amino
acids
Sugars
Glycerol
Fatty
acids
GLYCOLYSIS
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Figure 7.18-s5 The catabolism of various molecules from food (step 5)
Acetyl CoA
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
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48. Biosynthesis (Anabolic Pathways)
The body uses small molecules to build other substances
Some of these small molecules come directly from food; others can be produced during glycolysis or the citric acid cycle
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49. Figure 7.UN10-1
Figure 7.UN10-1 Skills exercise: making a bar graph and evaluating a hypothesis (part 1)
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50. Figure 7.UN10-2
Figure 7.UN10-2 Skills exercise: making a bar graph and evaluating a hypothesis (part 2)
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51. ATP NADH Inputs Outputs GLYCOLYSIS Glucose 2 Pyruvate 2 2
Figure 7.UN11
Inputs
Outputs
GLYCOLYSIS
Glucose
2 Pyruvate 2
ATP 2
NADH
Figure 7.UN11 Summary of key concepts: glycolysis
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52. CO2 F A DH2 Inputs Outputs 2 Pyruvate 2 Acetyl CoA 2 ATP 8 NADH CITRIC
Figure 7.UN12
Inputs
Outputs
2 Pyruvate
2 Acetyl CoA 2
ATP 8
NADH
CITRIC
ACID
CYCLE
2 Oxaloacetate 6
CO2 2
F A DH2
Figure 7.UN12 Summary of key concepts: citric acid cycle
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53. Cyt c IV Q III I II INTERMEMBRANE SPACE H+ H+ H+ Protein complex
Figure 7.UN13
INTERMEMBRANE
SPACE H+ H+ H+
Cyt c
Protein complex
of electron
carriers IV Q
III I
Figure 7.UN13 Summary of key concepts: electron transport chain II
2 H+ O2
+ ½
H2O
FA DH2
FAD
NA DH
NAD+
MITOCHONDRIAL MATRIX
(carrying electrons from food)
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54. ATP INTER- MEMBRANE SPACE H+ ATP synthase ADP + P H+ MITO CHONDRIAL
Figure 7.UN14
INTER-
MEMBRANE
SPACE H+
MITO
CHONDRIAL
MATRIX
ATP
synthase
Figure 7.UN14 Summary of key concepts: chemiosmosis
ADP + P H+
ATP i
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55. across membrane pH difference
Figure 7.UN15
across membrane
pH difference
Figure 7.UN15 Test your understanding, question 8 (pH vs. time)
Time
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56. Phosphofructokinase activity Fructose 6-phosphate concentration
Figure 7.UN16
Low ATP
concentration
Phosphofructokinase
activity
High ATP
concentration
Figure 7.UN16 Test your understanding, question 9 (regulation of phosphofructokinase)
Fructose 6-phosphate
concentration
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57. Figure 7.UN17 Test your understanding, question 13 (Coenzyme Q)
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