1. Cellular Respiration and Fermentation
Chapter 9
Cellular Respiration and Fermentation

2. Figure 9.1
Figure 9.1 How do these leaves power the work of life for this chimpanzee?

3. Photosynthesis in chloroplasts Cellular respiration in mitochondria
Figure 9.2
Light energy
ECOSYSTEM
Photosynthesis in chloroplasts
 O2
Organic molecules
CO2  H2O
Cellular respiration in mitochondria
Figure 9.2 Energy flow and chemical recycling in ecosystems.
ATP powers most cellular work
ATP
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 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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5. 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
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
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6. Redox Reactions: Oxidation and Reduction
transfer of electrons during chemical reactions releases energy stored in organic molecules
released energy is ultimately used to synthesize ATP
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7. The Principle of Redox
Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions
oxidation - a substance loses electrons, or is oxidized
reduction - a substance gains electrons, or is reduced (the amount of positive charge is reduced)
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8. becomes oxidized (loses electron) becomes reduced (gains electron)
Figure 9.UN01
becomes oxidized (loses electron)
becomes reduced (gains electron)
Figure 9.UN01 In-text figure, p. 164

9. becomes oxidized becomes reduced
Figure 9.UN02
becomes oxidized
becomes reduced
Figure 9.UN02 In-text figure, p. 164

10. Redox LEO – loses electrons and is oxidized
GER –gains electrons and is reduced
Reducing agent – gives away the electrons
Oxidizing agent – receives the electrons

11. Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel (such as glucose) is oxidized, and O2 is reduced
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12. becomes oxidized becomes reduced
Figure 9.UN03
becomes oxidized
becomes reduced
Figure 9.UN03 In-text figure, p. 165

13. The Stages of Cellular Respiration: A Preview
Harvesting of energy from glucose 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)
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14. Glycolysis
2 Net ATP
2 NADH
2 pyruvate molecules

15. Electrons carried via NADH Substrate-level phosphorylation
Figure 9.6-1
Electrons carried via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
MITOCHONDRION
Figure 9.6 An overview of cellular respiration.
ATP
Substrate-level phosphorylation

16. Electrons carried via NADH Electrons carried via NADH and FADH2
Figure 9.6-2
Electrons carried via NADH
Electrons carried via NADH and FADH2
Pyruvate oxidation
Glycolysis
Citric acid cycle
Glucose
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
Figure 9.6 An overview of cellular respiration.
ATP
ATP
Substrate-level phosphorylation
Substrate-level phosphorylation

17. Electrons carried via NADH Electrons carried via NADH and FADH2
Figure 9.6-3
Electrons carried via NADH
Electrons carried via NADH and FADH2
Oxidative phosphorylation: electron transport and chemiosmosis
Pyruvate oxidation
Glycolysis
Citric acid cycle
Glucose
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
Figure 9.6 An overview of cellular respiration.
ATP
ATP
ATP
Substrate-level phosphorylation
Substrate-level phosphorylation
Oxidative phosphorylation

18. The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
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19. Glycolysis Glucose broken down to 2 pyruvate
9 intermediates (with own enzyme) occur in the process
Cell reduces 2 NAD+ to NADH
2 ATP formed by substrate phosphorylatino
Pyruvate moved to mitochondria (by active transport)

20. Glycolysis (cont.) Glycolysis occurs in the cytosol
Does not require oxygen
4 ATP produced but 2 used to convert glucose to the intermediates.

21. Energy Investment Phase
Figure 9.8
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 9.8 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+

22. MITOCHONDRION CYTOSOL CO2 Coenzyme A NAD NADH + H Acetyl CoA
Figure 9.10
MITOCHONDRION
CYTOSOL
CO2
Coenzyme A 1 3 2
NAD
NADH
+ H
Acetyl CoA
Figure 9.10 Oxidation of pyruvate to acetyl CoA, the step before the citric acid cycle.
Pyruvate
Transport protein

23. Pyruvate Prep for Citric Acid cycle
Pyruvate converted to acetyl CoA-----
Carboxyl group (-COO-) removed from pyruvate and given off as CO2.
Two carbons remaining are oxidized to form acetic acid
NAD+ is reduced to NADH
Coenzyme A joins the two carbons and forms acetyl CoA
1 glucose produces 2 Acetyl CoA

24. Pyruvate CO2 NAD CoA NADH + H Acetyl CoA CoA CoA Citric acid cycle
Figure 9.11
Pyruvate
CO2
NAD
CoA
NADH
+ H
Acetyl CoA
CoA
CoA
Citric acid cycle
2 CO2
Figure 9.11 An overview of pyruvate oxidation and the citric acid cycle.
FADH2
3 NAD
FAD
3 NADH
+ 3 H
ADP + P i
ATP

25. Citric Acid Cycle Acetyl CoA enters cycle Joins 4 carbon molecules
Redox reactions occur and release CO2
4 carbon molecule regenerated
Occurs twice
1 ATP 1 FADH2
3 NADH

26. Citric acid cycle Figure 9.12-8 Acetyl CoA Oxaloacetate Malate Citrate
CoA-SH
NADH
+ H 1
H2O
NAD
Oxaloacetate 8 2
Malate
Citrate
Isocitrate
NAD
Citric acid cycle
NADH 3 7
+ H
H2O
CO2
Fumarate
CoA-SH
-Ketoglutarate
Figure 9.12 A closer look at the citric acid cycle. 4 6
CoA-SH 5
FADH2
CO2
NAD
FAD
Succinate
P i
NADH
GTP
GDP
Succinyl CoA
+ H
ADP
ATP

27. The Pathway of Electron Transport
inner membrane (cristae) of the mitochondrion
exist in multiprotein complexes
3 proteins transport H+ across the membrane
A H+ gradient results
An ATP synthase is built into the membrane
The synthase attach phosphates to ADP
The oxygen in the matrix accepts the electrons from the chain and bonds two H ions to form
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28. Electrons are transferred from NADH or FADH2 to the electron transport chain
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29. Multiprotein complexes I 40 II
Figure 9.13
NADH 50
2 e
NAD
FADH2
2 e
FAD
Multiprotein complexes I 40
FMN II
FeS
FeS Q
III
Cyt b 30
FeS
Cyt c1 IV
Free energy (G) relative to O2 (kcal/mol)
Cyt c
Cyt a
Cyt a3 20
Figure 9.13 Free-energy change during electron transport. 10
2 e
(originally from NADH or FADH2)
2 H + 1/2 O2
H2O

30. INTERMEMBRANE SPACE H Stator Rotor Internal rod Catalytic knob ADP +
Figure 9.14
INTERMEMBRANE SPACE H
Stator
Rotor
Internal rod
Figure 9.14 ATP synthase, a molecular mill.
Catalytic knob
ADP +
P i
ATP
MITOCHONDRIAL MATRIX

31. Protein complex of electron carriers
Figure 9.15 H H H
Protein complex of electron carriers H
Cyt c IV Q
III I
ATP synth- ase II
2 H + 1/2O2
H2O
FADH2
FAD
Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis.
NAD
NADH
ADP  P i
ATP
(carrying electrons from food) H 1
Electron transport chain 2
Chemiosmosis
Oxidative phosphorylation

32. 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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33. 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 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 is not known exactly
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34. Oxidative phosphorylation: electron transport and chemiosmosis
Figure 9.16
Electron shuttles span membrane
MITOCHONDRION
2 NADH or
2 FADH2
2 NADH
2 NADH
6 NADH
2 FADH2
Oxidative phosphorylation: electron transport and chemiosmosis
Glycolysis
Pyruvate oxidation
Citric acid cycle
Glucose
2 Pyruvate
2 Acetyl CoA
Figure 9.16 ATP yield per molecule of glucose at each stage of cellular respiration.
 2 ATP
 2 ATP
 about 26 or 28 ATP
About 30 or 32 ATP
Maximum per glucose:
CYTOSOL

35. Concept 9.5: 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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36. 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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37. 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
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38. i i   Figure 9.17 2 ATP  2 ATP Glucose Glycolysis Glucose
2 ADP  2 P i
2 ATP
2 ADP  2 P i
2 ATP
Glucose
Glycolysis
Glucose
Glycolysis
2 Pyruvate 2
NAD 
2 NADH
2 CO2 2
NAD 
2 NADH 
2 H 
2 H
2 Pyruvate
Figure 9.17 Fermentation.
2 Ethanol
2 Acetaldehyde
2 Lactate
(a) Alcohol fermentation
(b) Lactic acid fermentation

39. In lactic acid fermentation, pyruvate is reduced to 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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40.   2 ADP  2 P i 2 ATP Glucose Glycolysis 2 NAD 2 NADH  2 H
Figure 9.17b
2 ADP  2 P i
2 ATP
Glucose
Glycolysis
2 NAD 
2 NADH 
2 H 
2 Pyruvate
Figure 9.17 Fermentation.
2 Lactate
(b) Lactic acid fermentation

41. Comparing Fermentation with Anaerobic and Aerobic Respiration
All use glycolysis
In all three, NAD+ is the oxidizing agent that
The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration
Cellular respiration produces 32 ATP per glucose molecule;
fermentation produces 2 ATP per glucose molecule
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42. Obligate anaerobes carry out 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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43. 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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44. Concept 9.6: 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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45. 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; amino groups can feed glycolysis or the citric acid cycle
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46. Fatty acids are broken down by beta oxidation and yield acetyl CoA
Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA)
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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47. Biosynthesis (Anabolic Pathways)
The body uses small molecules to build other substances
These small molecules may come directly from food, from glycolysis, or from the citric acid cycle
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48. Regulation of Cellular Respiration via Feedback Mechanisms
Feedback inhibition is the most common mechanism for control
If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down
Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway
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