1. Get used to this picture….
Figure 7.2
Get used to this picture….
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 1

2. Key points you need to take away from this unit
Mitochondria
Mitochondria have a double membrane that allows compartmentalization within the mitochondria and is important to its function
The outer membrane is smooth, but the inner membrane is highly convoluted, forming folds called cristae
Cristae contain enzymes important to ATP production; cristae also increase the surface area for ATP production

3. Key points you need to take away from this unit
Glycolysis/Citric Acid Cycle
Glycolysis rearranges the bonds in glucose molecules, releasing free energy to form ATP from ADP and inorganic phosphate, and resulting in the production of pyruvate
Pyruvate is transported from the cytoplasm to the mitochondrion, where further oxidation occurs.
In the Krebs cycle, CO2 is released from organic intermediates ATP is synthesized from ADP and inorganic phosphate via substrate level phosphorylation and electrons are captured by coenzymes
Electrons that are extracted in the series of Krebs cycle reaction are carried by NADH and FADH2 to the electron transport chain

4. Key points you need to take away from this unit
Oxidative phosphorylation
Electron transport chain reactions occur in chloroplasts, mitochondria, and prokaryotic plasma membranes
In cellular respiration, electrons delivered by NADH and FADH2 are passed to a series of electron acceptors as they move toward the terminal electron acceptor, oxygen.
The passage of e- is accompanied by the formation of a H+ gradient across the inner mitochondrial membrane, with the membrane separating a region of high [H+] from a region of low [H+]. In prokaryotes, the passage of e- is accompanied by the outward movement of H+ across the plasma membrane
The flow of H+ back through the membrane-bound ATP synthase by chemiosmosis generaties ATP from ADP and inorganic phosphate.
In cellular respiration, decoupling oxidative phosphorylation from e- transport is involved with thermoregulation

5. Where we started…..
Energy flows through nature in the form of chemical energy, which is stored in bonds, especially C-C, C-H
Mitochondria are the site of energy production in eukaryotic cells
Compounds can be oxidized or reduced, in respiration, fuels (glucose) are oxidized while O2 is reduced
Respiration has three main steps: Glycolysis, Citric Acid Cyle, and Oxidative Phosphorylation (ETC)
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6. From last time…..
Glycolysis is the breakdown of glucose, takes place in the cytoplasm, and occurs whether or not O2 is available
There are 2 phases of glycolysis: energy investment, energy payoff
It takes 2 ATP to get glycolysis going, but the pathway yields 4 ATP, leading to a net of 2 ATP
NAD+ is reduced to NADH which shuttles e- to the ETC
Pyruvate enters the mitochondria by diffusion through channel proteins, and is oxidized into CO2 and acetyl-CoA which is used in the Citric Acid cycle
Ready?

7. 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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8. The cycle oxidizes organic fuel derived from pyruvate, generating:
Figure 7.10
Pyruvate
(from glycolysis,
2 molecules per glucose)
CYTOSOL
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
1 FADH2
per turn, with 2 turns/glucose
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 8

9. 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 9

10. 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 10

11. (a) Uncontrolled reaction (b) Cellular respiration
Figure 7.5
H2  O2
2 H  O2
Controlled
release of
energy
2 H  2 e−
ATP
ATP
Explosive
release
Electron transport
chain
Free energy, G
Free energy, G
ATP
2 e−
Figure 7.5 An introduction to electron transport chains O2
2 H
H2O
H2O
(a) Uncontrolled reaction
(b) Cellular respiration 11

12. The Pathway of Electron Transport
The electron transport chain is in the inner membrane of the mitochondrion
Most of the chain’s components are proteins, which exist in multiprotein complexes
Some of these proteins are “cytochromes” and contain Fe atoms
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
In prokaryotes, this process takes place in the plasma membrane (this is important)
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13. Electron transport chain Oxidative phosphorylation
Figure 7.14
Here’s a closer look
Intermembrane space H H
Protein
complex
of electron
carriers H H
Cyt c IV Q
III I
Glycolysis
&
ATP
synthase II
2 H  ½ O2
Krebs cycle
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
Matrix 13

14. 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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15. So then, where does the ATP get generated?
Figure 7.14b
So then, where does the ATP get generated?
ATPase is an integral membrane protein
More of a motor than an enzyme
Allows H+ to pass through by chemiosmosis
As this happens the H+ release free energy (ie. exergonic) which is used to do work – make ATP
This gradient is called the proton-motive force due to its ability to do work H
ATP
synthase
Figure 7.14b Chemiosmosis couples the electron transport chain to ATP synthesis (part 2: chemiosmosis)
ADP  P
ATP i H 2
Chemiosmosis 15

16. Video: ATP Synthase 3-D Side View
Video: ATP Synthase 3-D Top View
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17. So, this is the forest, and the trees
Figure 7.15
So, this is the forest, and the trees
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:
Can you draw this process? Can you explain it? 17

18. Tally of the ATP
During cellular respiration, most energy flows in the following sequence:
glucose  NADH  electron transport chain  proton-motive force  ATP
The ETC produces ~26-28 ATP
Glycolysis = 2 ATP net
Krebs = 2 ATP (1/turn, 2 turns/glucose)
Therefore the total generated = 36 (or 34 depending on who you ask)
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20. 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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21. 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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22. 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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23. 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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24. (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 24

25. (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 25

26. (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 26

27. 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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28. 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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29. 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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30. 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 30

31. 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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32. 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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33. The Versatility of Catabolism
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
Fats are digested to glycerol 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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34. 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 34

35. 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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36. Inputs Glycolysis Glucose ATP  2 NADH
Figure 7.UN11
Inputs
Outputs
Glycolysis
Glucose
2 Pyruvate  2
ATP
 2
NADH
Figure 7.UN11 Summary of key concepts: pyruvate 36

37. CO2 Inputs Outputs 2 Pyruvate 2 Acetyl CoA 2 ATP 8 NADH Citric acid
Figure 7.UN12
Inputs
Outputs
2 Pyruvate
2 Acetyl CoA 2
ATP 8
NADH
Citric
acid
cycle
2 Oxaloacetate
CO2 6 2
FADH2
Figure 7.UN12 Summary of key concepts: citric acid cycle 37

39. 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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