CAMPBELL BIOLOGY IN FOCUS
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Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
7 Cellular
Respiration
and Fermentation
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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Figure 7.1
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
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Video: Carbon Cycle
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Figure 7.2
Light energy
ECOSYSTEM
Photosynthesis in chloroplasts
CO2 H2O
Cellular respiration in mitochondria
Organic molecules
O2
ATP ATP powers most cellular work
Heat energy
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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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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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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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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The Principle of Redox
Chemical reactions that transfer electrons between
reactants are called oxidation-reduction reactions, or
redox reactions
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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Figure 7.UN01
becomes oxidized (loses electron)
becomes reduced (gains electron)
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Figure 7.UN02
becomes oxidized
becomes reduced
The electron donor is called the reducing agent
The electron acceptor is called the oxidizing agent
Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds
An example is the reaction between methane and O2
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Figure 7.3
Reactants Products
Methane (reducing
agent)
Oxygen (oxidizing
agent)
Carbon dioxide Water
becomes reduced
becomes oxidized
Redox reactions that move electrons closer to
electronegative atoms, like oxygen, release chemical
energy that can be put to work
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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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Figure 7.UN03
becomes oxidized
becomes reduced
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
As an electron acceptor, NAD functions as an
oxidizing agent during cellular respiration
Each NADH (the reduced form of NAD) represents
stored energy that is tapped to synthesize ATP
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Figure 7.4
NAD
Nicotinamide (oxidized form)
Nicotinamide (reduced form)
Oxidation of NADH
Reduction of NAD
Dehydrogenase NADH
2[H] (from food)
2 e− 2 H
2 e− H
H
H
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Figure 7.4a
NAD
Nicotinamide (oxidized form)
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Figure 7.4b
Nicotinamide (reduced form)
Oxidation of NADH
Reduction of NAD
Dehydrogenase NADH
2 e− 2 H
2 e− H
H
H 2[H] (from food)
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Figure 7.UN04
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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Figure 7.5
Explosive
release
(a) Uncontrolled reaction (b) Cellular respiration
H2O
Fre
e e
nerg
y,
G
Fre
e e
nerg
y,
G
Controlled release of
energy
H2O
2 H
2 e−
2 H 2 e−
ATP
ATP
ATP
½
½
½ H2 O2
O2
O2
2 H
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
(completes the breakdown of glucose)
Oxidative phosphorylation (accounts for most of
the ATP synthesis)
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Animation: Cellular Respiration
Right click slide / Select play
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Figure 7.UN05
Glycolysis (color-coded teal throughout the chapter)
Pyruvate oxidation and the citric acid cycle
(color-coded salmon)
1.
Oxidative phosphorylation: electron transport and
chemiosmosis (color-coded violet)
2.
3.
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Figure 7.6-1
Electrons via NADH
Glycolysis
Glucose Pyruvate
CYTOSOL
ATP
Substrate-level
MITOCHONDRION
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Figure 7.6-2
Electrons via NADH
Glycolysis
Glucose Pyruvate
Pyruvate oxidation
Acetyl CoA
Citric acid cycle
Electrons via NADH and
FADH2
CYTOSOL
ATP
Substrate-level
ATP
Substrate-level
MITOCHONDRION
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Figure 7.6-3
Electrons via NADH
Glycolysis
Glucose Pyruvate
Pyruvate oxidation
Acetyl CoA
Citric acid cycle
Electrons via NADH and
FADH2
Oxidative phosphorylation: electron transport
and chemiosmosis
CYTOSOL
ATP
Substrate-level
ATP
Substrate-level
MITOCHONDRION
ATP
Oxidative
The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
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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 by substrate-level
phosphorylation
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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Figure 7.7
Substrate
P
ADP
Product
ATP
Enzyme Enzyme
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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Figure 7.UN06
Glycolysis Pyruvate
oxidation
Citric acid cycle
Oxidative
phosphorylation
ATP ATP ATP
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Figure 7.8
Energy Investment Phase
Energy Payoff Phase
Net
Glucose
Glucose
2 ADP 2 P
4 ADP 4 P
2 NAD 4 e− 4 H
2 NAD 4 e− 4 H
4 ATP formed − 2 ATP used
2 ATP
4 ATP
used
formed
2 NADH 2 H
2 Pyruvate 2 H2O
2 Pyruvate 2 H2O
2 NADH 2 H
2 ATP
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Figure 7.9a
Glycolysis: Energy Investment Phase
Glucose ATP
ADP
Glucose 6-phosphate
Phosphogluco-
isomerase
Hexokinase
1 2 3
4
ATP
ADP
Fructose 6-phosphate
Phospho-
fructokinase
Fructose 1,6-bisphosphate
Aldolase
Isomerase
5
Glyceraldehyde 3-phosphate (G3P)
Dihydroxyacetone phosphate (DHAP)
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Figure 7.9aa-1
Glycolysis: Energy Investment Phase
Glucose
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Figure 7.9aa-2
Glycolysis: Energy Investment Phase
Glucose Glucose
6-phosphate
ADP
ATP
Hexokinase
1
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Figure 7.9aa-3
Glycolysis: Energy Investment Phase
Glucose Glucose
6-phosphate
ADP
ATP
Hexokinase
1
Fructose 6-phosphate
Phosphogluco-
isomerase
2
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Figure 7.9ab-1
Glycolysis: Energy Investment Phase
Fructose 6-phosphate
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Figure 7.9ab-2
Glycolysis: Energy Investment Phase
Fructose 6-phosphate
Phospho-
fructokinase
3
Fructose 1,6-bisphosphate
ATP
ADP
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Figure 7.9ab-3
Glycolysis: Energy Investment Phase
Fructose 6-phosphate
Phospho-
fructokinase
3
Aldolase
Isomerase
4
5
Fructose 1,6-bisphosphate
Glyceraldehyde 3-phosphate (G3P)
ATP
ADP
Dihydroxyacetone phosphate (DHAP)
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Figure 7.9b
Glycolysis: Energy Payoff Phase
2 NAD Glyceraldehyde
3-phosphate (G3P)
Triose
phosphate
dehydrogenase
6
2 H
2 NADH
2
2 P i
1,3-Bisphospho- glycerate
3-Phospho- glycerate
2-Phospho- glycerate
Phosphoenol-
pyruvate (PEP)
Pyruvate
Phospho-
glycerokinase
Phospho-
glyceromutase
Enolase Pyruvate
kinase
2 ADP 2 2 2 2 2 ADP
2 ATP 2 H2O
2 ATP
9 10 8 7
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Figure 7.9ba-1
Isomerase
4
Glyceraldehyde 3-phosphate (G3P)
Dihydroxyacetone phosphate (DHAP)
Glycolysis: Energy Payoff Phase
Aldolase 5
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Figure 7.9ba-2
Isomerase
Glyceraldehyde 3-phosphate (G3P)
Dihydroxyacetone phosphate (DHAP)
Glycolysis: Energy Payoff Phase
2 NAD
Triose phosphate
dehydrogenase
2 H
2 NADH
2
1,3-Bisphospho- glycerate
2
Aldolase
P i
5 6
4
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Figure 7.9ba-3
Isomerase
Glyceraldehyde 3-phosphate (G3P)
Dihydroxyacetone phosphate (DHAP)
Glycolysis: Energy Payoff Phase
2 NAD
Triose phosphate
dehydrogenase
2 H
2 NADH
2
1,3-Bisphospho- glycerate
3-Phospho- glycerate
Phospho- glycerokinase
2 ADP
2 ATP
2
Aldolase
P i
2
5 7 6
4
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Figure 7.9bb-1
3-Phospho- glycerate
Glycolysis: Energy Payoff Phase
2
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Figure 7.9bb-2
8 3-Phospho- glycerate
Glycolysis: Energy Payoff Phase
Phospho- glyceromutase
2 2 2
2 H2O
2-Phospho- glycerate
Phosphoenol- pyruvate (PEP)
Enolase
9
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Figure 7.9bb-3
3-Phospho- glycerate
Glycolysis: Energy Payoff Phase
2 ATP
Phospho- glyceromutase
2 2 2 2 2 ADP
2 H2O
2-Phospho- glycerate
Phosphoenol- pyruvate (PEP)
Pyruvate
Enolase Pyruvate kinase
9 10 8
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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Figure 7.UN07
Glycolysis Pyruvate
oxidation
Citric acid cycle
Oxidative
phosphorylation
ATP ATP ATP
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Figure 7.10
CYTOSOL Pyruvate (from glycolysis, 2 molecules per glucose)
CO2
CoA NAD
NADH
MITOCHONDRION CoA
CoA
Acetyl CoA H
Citric acid cycle
FADH2
FAD
ADP P i
ATP
NADH
3 NAD
3
3 H
2 CO2
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Figure 7.10a
CYTOSOL Pyruvate (from glycolysis, 2 molecules per glucose)
CO2
CoA NAD
NADH
MITOCHONDRION CoA
Acetyl CoA H
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Figure 7.10b
CoA
Citric
acid
cycle FADH2
FAD
ADP P i
ATP
NADH
3 NAD
3
3 H
2 CO2
CoA
Acetyl CoA
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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Figure 7.UN08
Glycolysis Pyruvate
oxidation
Oxidative
phosphorylation
ATP ATP ATP
Citric acid cycle
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Figure 7.11-1
Acetyl CoA
Oxaloacetate
CoA-SH
Citrate
H2O
Isocitrate
Citric acid cycle
2
1
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Figure 7.11-2
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD
H
CO2
-Ketoglutarate
Citric acid cycle
3
1
CoA-SH
2
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Figure 7.11-3
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD
H
CO2
-Ketoglutarate
Citric acid cycle
CoA-SH
CO2 NAD
NADH
H Succinyl CoA
4
1
3
CoA-SH
2
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Figure 7.11-4
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD
H
CO2
-Ketoglutarate
Citric acid cycle
CoA-SH
CO2 NAD
NADH
H
ATP formation
Succinyl CoA
ADP
GDP GTP
P i
ATP
Succinate
5
4
1
CoA-SH
3
CoA-SH
2
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Figure 7.11-5
Malate
Succinate
FAD
FADH2
Fumarate
H2O 7
6
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD
H
CO2
-Ketoglutarate
Citric acid cycle
CoA-SH
CO2 NAD
NADH
H
ATP formation
Succinyl CoA
ADP
GDP GTP
P i
ATP
5
4
1
CoA-SH
3
CoA-SH
2
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Figure 7.11-6
NADH
NAD
H
8
Malate
Succinate
FAD
FADH2
Fumarate
H2O 7
6
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD
H
CO2
-Ketoglutarate
Citric acid cycle
CoA-SH
CO2 NAD
NADH
H
ATP formation
Succinyl CoA
ADP
GDP GTP
P i
ATP
5
4
1
CoA-SH
3
CoA-SH
2
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Figure 7.11a
CoA-SH
Acetyl CoA
Start: Acetyl CoA adds its two-carbon group to oxaloacetate, producing citrate; this is a highly exergonic reaction.
Oxaloacetate
Citrate
Isocitrate
H2O 1
2
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Figure 7.11b
Isocitrate Redox reaction: Isocitrate is oxidized; NAD is reduced.
Redox reaction: After CO2 release, the resulting four-carbon molecule is oxidized (reducing NAD), then made reactive by addition of CoA.
CO2 release
CO2 release
-Ketoglutarate
Succinyl CoA
NAD
NADH
H
CO2
CO2
CoA-SH
NAD
NADH
H
3
4
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Figure 7.11c
CoA-SH
Redox reaction: Succinate is oxidized; FAD is reduced.
Fumarate
Succinate
Succinyl CoA
ATP formation
ATP
ADP
GDP GTP
FAD
FADH2
P i
5
6
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Figure 7.11d
Redox reaction: Malate is oxidized; NAD is reduced.
Fumarate
Malate
Oxaloacetate
H2O
NAD
H
NADH
7
8
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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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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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
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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Figure 7.UN09
Glycolysis Pyruvate
oxidation
Citric acid cycle
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP ATP ATP
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Figure 7.12
Multiprotein complexes
(originally from NADH or FADH2)
Fre
e e
nerg
y (
G)
rela
tive t
o O
2 (
kcal/m
ol)
50
40
30
20
10
0
NADH
NAD
FADH2
FAD
2
2
e−
e−
FMN
Fe•S Fe•S
Q
I II
III Cyt b
Cyt c1
Fe•S
Cyt c IV
Cyt a
Cyt a3
2 e−
O2 2 H ½
H2O
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Figure 7.12a
Multiprotein complexes
Fre
e e
nerg
y (
G)
rela
tive t
o O
2 (
kcal/m
ol)
50
40
30
20
10
NADH
NAD
FADH2
FAD
2
2
e−
e−
FMN
Fe•S Fe•S
Q
I
II
III Cyt b
Cyt c1
Fe•S
Cyt c IV
Cyt a
Cyt a3
2 e−
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Figure 7.12b
30
20
10
0
Cyt c1
Cyt c IV
Cyt a
Cyt a3
2 e−
Fre
e e
ne
rgy (
G)
rela
tive t
o O
2 (
kcal/
mo
l)
(originally from NADH or FADH2)
2 H ½ O2
H2O
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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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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Video: ATP Synthase 3-D Side View
Video: ATP Synthase 3-D Top View
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Figure 7.13
INTERMEMBRANE SPACE
MITOCHONDRIAL MATRIX
Rotor
Internal rod
Catalytic knob
Stator H
ATP
ADP
P i
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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© 2014 Pearson Education, Inc.
Figure 7.UN09
Glycolysis Pyruvate
oxidation
Citric acid cycle
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP ATP ATP
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Figure 7.14
Protein complex of electron carriers
H
H H
H
Q
I
II
III
FADH2 FAD
NAD NADH
(carrying electrons
from food)
Electron transport chain
Oxidative phosphorylation
Chemiosmosis
ATP
synthase
H
ADP ATP P i
H2O 2 H ½ O2
IV
Cyt c
1 2
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Figure 7.14a
Protein complex of electron carriers
H
Q
I
II
III
FADH2 FAD
NAD NADH
(carrying electrons
from food)
Electron transport chain
H2O 2 H ½ O2
Cyt c
1
IV
H H
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Figure 7.14b
ATP
synthase
Chemiosmosis 2
H
H
ADP P i
ATP
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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© 2014 Pearson Education, Inc.
Figure 7.15
Electron shuttles span membrane
CYTOSOL 2 NADH
2 NADH
2 FADH2
or
2 NADH
Glycolysis
Glucose 2 Pyruvate
Pyruvate oxidation
2 Acetyl CoA
Citric acid cycle
6 NADH 2 FADH2
Oxidative phosphorylation: electron transport
and chemiosmosis
about 26 or 28 ATP 2 ATP 2 ATP
About 30 or 32 ATP
Maximum per glucose:
MITOCHONDRION
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Figure 7.15a
Electron shuttles span membrane
2 NADH
2 FADH2
or
2 NADH
Glycolysis
Glucose 2 Pyruvate
2 ATP
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Figure 7.15b
2 NADH 6 NADH 2 FADH2
Citric acid cycle
Pyruvate oxidation
2 Acetyl CoA
2 ATP
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Figure 7.15c
2 NADH
2 NADH 6 NADH 2 FADH2
2 FADH2
or
Oxidative phosphorylation: electron transport
and chemiosmosis
about 26 or 28 ATP
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Figure 7.15d
Maximum per glucose: About
30 or 32 ATP
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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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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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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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
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Animation: Fermentation Overview
Right click slide / Select play
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Figure 7.16
2 ADP 2 2 ATP P i
Glucose Glycolysis
2 Pyruvate
2 CO2 2 NADH
2 H
2 NAD
2 Ethanol
(a) Alcohol fermentation
2 Acetaldehyde
(b) Lactic acid fermentation
2 Lactate
2 NADH
2 H
2 NAD
2 Pyruvate
Glycolysis
2 ATP 2 ADP 2 P i
Glucose
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Figure 7.16a
2 ADP 2 2 ATP P i
Glucose Glycolysis
2 Pyruvate
2 CO2 2 NADH
2 H
2 NAD
2 Ethanol
(a) Alcohol fermentation
2 Acetaldehyde
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Figure 7.16b
2 ADP 2 2 ATP P i
Glucose Glycolysis
2 Pyruvate
2 NADH
2 H
2 NAD
(b) Lactic acid fermentation
2 Lactate
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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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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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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© 2014 Pearson Education, Inc.
Figure 7.17 Glucose
CYTOSOL Glycolysis
Pyruvate
O2 present:
Aerobic cellular
respiration
No O2 present:
Fermentation
Ethanol, lactate, or
other products
Acetyl CoA
Citric acid cycle
MITOCHONDRION
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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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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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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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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© 2014 Pearson Education, Inc.
Figure 7.18-1
Proteins
Amino acids
Carbohydrates
Sugars
Fats
Glycerol Fatty acids
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Figure 7.18-2
Proteins
Amino acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
NH3
Fats
Glycerol Fatty acids
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Figure 7.18-3
Proteins
Amino acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
Acetyl CoA
NH3
Fats
Glycerol Fatty acids
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Figure 7.18-4
Proteins
Amino acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
Acetyl CoA
Citric acid cycle
NH3
Fats
Glycerol Fatty acids
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Figure 7.18-5
Proteins
Amino acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
Acetyl CoA
Citric acid cycle
NH3
Fats
Glycerol Fatty acids
Oxidative phosphorylation
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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© 2014 Pearson Education, Inc.
Figure 7.UN10a
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Figure 7.UN10b
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Figure 7.UN11
Inputs
Glucose
Glycolysis
2 Pyruvate 2
Outputs
ATP NADH 2
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Figure 7.UN12
Inputs
2 Pyruvate 2 Acetyl CoA
2 Oxaloacetate Citric
acid
cycle
Outputs
ATP
CO2
2
6 2
8 NADH
FADH2
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Figure 7.UN13a
Protein complex of electron carriers
INTERMEMBRANE SPACE
MITOCHONDRIAL MATRIX (carrying electrons from food)
NADH NAD
FADH2 FAD
Cyt c
Q
I
II
III
IV
2 H ½O2 H2O
H
H H
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Figure 7.UN13b
INTER- MEMBRANE SPACE
MITO- CHONDRIAL MATRIX
ATP synthase
ATP ADP H
H
P i
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Figure 7.UN14
Time
pH
dif
fere
nc
e
acro
ss m
em
bra
ne