1. Cellular Respiration and Fermentation7
Cellular Respiration and Fermentation

2. Aim: How can we describe the internal mechanisms required in respiration? Do Now: Describe the chemical equation for respiration. Homework: Complete Chapter 7 concept questions due Monday.

3. 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.
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.
Animation: Carbon Cycle
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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
Figure 7.2 Energy flow and chemical recycling in ecosystems
ATP powers
most cellular work
ATP
Heat
energy 4

5. Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic.
Fermentation is a partial break down of sugars that occurs without O.
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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6. 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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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.
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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8. 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 synthesis.
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9. becomes oxidized becomes reduced
Figure 7.UN03
becomes oxidized
becomes reduced
Figure 7.UN03 In-text figure, cellular respiration redox reaction, p. 137 9

10. 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.
NAD is an electron acceptor.
Each NADH represents stored energy that is tapped to synthesize ATP.
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11. 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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12. The Stages of Cellular Respiration: A Preview
Harvesting of energy from glucose has three stages:
1. Glycolysis (breaks down glucose into two molecules of pyruvate).
2. Pyruvate oxidation and the citric acid cycle (completes the breakdown of glucose).
3. Oxidative phosphorylation (accounts for most of the ATP synthesis).
Animation: Cellular Respiration
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13. Electrons via NADH Glycolysis Glucose Pyruvate CYTOSOL MITOCHONDRION
Figure 7.6-1
Electrons
via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
MITOCHONDRION
Figure An overview of cellular respiration (step 1)
ATP
Substrate-level 13

14. Electrons via NADH and FADH2 Electrons via NADH Pyruvate oxidation
Figure 7.6-2
Electrons
via NADH and
FADH2
Electrons
via NADH
Pyruvate
oxidation
Glycolysis
Citric
acid
cycle
Glucose
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
Figure An overview of cellular respiration (step 2)
ATP
ATP
Substrate-level
Substrate-level 14

15. 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 15

16. The step that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions (STEP # 3).
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17. Aim: How can we describe glycolysis, pyruvate oxidation, and citric acid cycle? Do Now: Describe the overall goal of cellular respiration. Homework: Exam Friday Chapter 5 and 7.

18. 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.
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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19. 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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20. Citric acid cycle Oxidative phosphorylation Pyruvate oxidation
Figure 7.UN06
Citric
acid
cycle
Oxidative
phosphorylation
Pyruvate
oxidation
Glycolysis
Figure 7.UN06 In-text figure, mini-map, glycolysis, p. 140
ATP
ATP
ATP 20

21. 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 21

24. 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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25. Citric acid cycle Oxidative phosphorylation Pyruvate oxidation
Figure 7.UN07
Citric
acid
cycle
Oxidative
phosphorylation
Pyruvate
oxidation
Glycolysis
Figure 7.UN07 In-text figure, mini-map, pyruvate oxidation, p. 142
ATP
ATP
ATP 25

26. 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 26

27. Citric acid cycle Acetyl CoA CoA CoA 2 CO2 FADH2 3 NAD 3 NADH FAD
Figure 7.10b
Acetyl CoA
CoA
CoA
Citric
acid
cycle 2
CO2
FADH2
3 NAD
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 27

28. 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
Figure 7.10 An overview of pyruvate oxidation and the citric acid cycle 2
CO2
FADH2
3 NAD
FAD 3
NADH
 3 H
ADP  P i
ATP 28

29. The citric acid cycle, also called the Krebs cycle, completes the breakdown of pyruvate to CO2.
Products of the citric acid cycle: 1 ATP, 3 NADH, and 1 FADH2 per turn.
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30. Citric acid cycle Oxidative phosphorylation Pyruvate oxidation
Figure 7.UN08
Citric
acid
cycle
Oxidative
phosphorylation
Pyruvate
oxidation
Glycolysis
Figure 7.UN08 In-text figure, mini-map, citric acid cycle, p. 143
ATP
ATP
ATP 30

31. **OVERVIEW OF STEPS**
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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32. Aim: How can we describe the electron transport chain
Aim: How can we describe the electron transport chain? Do Now: Does oxygen have to be present in order for respiration to occur?

33. 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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34. 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 multi-protein 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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35. 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 35

36. Free energy (G) relative to O2 (kcal/mol)
Figure 7.12
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
Free energy (G) relative to O2 (kcal/mol)
Cyt c
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 36

37. Electrons are passed through a number of proteins
Electrons are transferred from NADH or FADH2 to the electron transport chain
Electrons are passed through a number of proteins
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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38. Chemiosmosis: The Energy-Coupling Mechanism
Electron transfer in the electron transport chain causes proteins to pump H from the mitochondrial matrix to the inter-membrane 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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39. Video: ATP Synthase 3-D Side View
Video: ATP Synthase 3-D Top View
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40. 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 40

41. 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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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. 146
ATP
ATP
ATP 42

43. 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
Figure 7.14 Chemiosmosis couples the electron transport chain to ATP synthesis
ADP  P
ATP i
(carrying electrons
from food) H 1
Electron transport chain 2
Chemiosmosis
Oxidative phosphorylation 43

44. Electron transport chain
Figure 7.14a H H
Protein
complex
of electron
carriers H
Cyt c IV Q
III I II
2 H  ½ O2
H2O
FADH2
FAD
Figure 7.14a Chemiosmosis couples the electron transport chain to ATP synthesis (part 1: electron transport chain)
NAD
NADH
(carrying electrons
from food) 1
Electron transport chain 44

45. 2 ATP synthase Chemiosmosis H H ADP  ATP i P Figure 7.14b
Figure 7.14b Chemiosmosis couples the electron transport chain to ATP synthesis (part 2: chemiosmosis)
ADP  P
ATP i H 2
Chemiosmosis 45

46. 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.
The exact number of ATP released is not known.
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47. Electron shuttles span membrane MITOCHONDRION 2 NADH CYTOSOL or
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: 47

48. Aim: How can we describe chemiosmosis and fermentation
Aim: How can we describe chemiosmosis and fermentation? Do Now: Does every organism on earth require oxygen to respire? Explain.

49. 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.
If NO OXYGEN is present, glycolysis couples with fermentation or anaerobic respiration to produce ATP.
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50. Anaerobic respiration uses an electron transport chain with a final electron acceptor that is something other than O2, for example, sulfate.
Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP.
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51. Types of Fermentation
Fermentation consists of glycolysis plus reactions that regenerate NAD, which can be reused by glycolysis.
Two common types are:
alcohol fermentation
lactic acid fermentation
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52. In alcohol fermentation, pyruvate is converted to ethanol in two steps.
The first step releases CO2 from pyruvate, and the second step reduces acetaldehyde to ethanol.
Alcohol fermentation by yeast is used in brewing, winemaking, and baking.
Animation: Fermentation Overview
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53. (a) Alcohol fermentation (b) Lactic acid fermentation
Figure 7.16
2 ADP  2 P
2 ADP  2 i
2 ATP 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 7.16 Fermentation
2 Ethanol
2 Acetaldehyde
2 Lactate
(a) Alcohol fermentation
(b) Lactic acid fermentation 53

54. (a) Alcohol fermentation
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 54

55. (b) Lactic acid fermentation
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 55

56. 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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57. 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.
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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58. 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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