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Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic + O
molecules 2
CO2 + H2O
Cellular respiration
in mitochondria
ATP
powers most cellular work
Heat
energy
Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is exergonic
• Fermentation is a partial degradation of sugars
that occurs without oxygen
• Cellular respiration consumes oxygen and
organic molecules and yields ATP
• Cellular Respiration Equation:
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The Principle of Redox
• Chemical reactions that transfer electrons
between reactants are called oxidation-reduction
reactions, or redox reactions
• Oxidation:
• Reduction:
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• The electron donor is called the reducing agent
• The electron receptor is called the oxidizing
agent
becomes oxidized
(loses electron)
Xe-
+
Y
X
+
becomes reduced
(gains electron)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Ye-
LE 9-3
Products
Reactants
becomes oxidized
CH4
2 O2
+
CO2
C
Energy
2 H2O
+
becomes reduced
H
H
+
H
O
O
O
C
O
H
O
H
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water
H
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration, the fuel (such as
glucose) is oxidized and oxygen is reduced:
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
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Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
• 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
• NADH represents stored energy that is tapped to
synthesize ATP
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LE 9-4
2 e– + 2 H+
NAD+
2 e– + H+
H+
NADH
Dehydrogenase
+ 2[H]
(from food)
Nicotinamide
(oxidized form)
+
Nicotinamide
(reduced form)
H+
• NADH passes the electrons to the electron
transport chain
• Oxygen pulls electrons down the chain in an
energy-yielding tumble
• The energy yielded is used to regenerate ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-5
H2 + 1/2 O2
+
2H
1 /2
O2
1/2
O2
(from food via NADH)
Explosive
release of
heat and light
energy
Free energy, G
Free energy, G
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e–
2
H+
H2O
Uncontrolled reaction
H2O
Cellular respiration
The Stages of Cellular Respiration: A Preview
• Cellular respiration 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)
NADH and
NADH
Glycolysis
Cytosol
ATP
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FADH2
Citric
electron transport
acid
and
cycle
Mitochondrion chemiosmosis
ATP
ATP
LE 9-6_1
Glycolysis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Substrate-level
phosphorylation
LE 9-6_2
Glycolysis
Pyruvate
Glucose
Cytosol
Citric
acid
cycle
Mitochondrion
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
LE 9-6_3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Animation: Cell Respiration Overview
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• Oxidative phosphorylation accounts for almost
90% of the ATP generated by cellular respiration
• A small amount of ATP is formed in glycolysis and
the citric acid cycle by substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
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+
Product
ATP
Concept 9.2: Glycolysis harvests energy by
oxidizing glucose to pyruvate
• Glycolysis (“splitting of sugar”) breaks down
glucose into two molecules of pyruvate
• Glycolysis occurs in the cytoplasm and has two
major phases:
– Energy investment phase
– Energy payoff phase
Animation: Glycolysis
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LE 9-8
Energy investment phase
Glucose
2 ATP used
2 ADP + 2 P
Glycolysis
Citric
acid
cycle
Oxidative
phosphorylation
Energy payoff phase
ATP
ATP
ATP
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Net
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
LE 9-9a_1
Glucose
ATP
Hexokinase
ADP
Glucose-6-phosphate
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
LE 9-9a_2
Glucose
ATP
Hexokinase
ADP
Glucose-6-phosphate
Phosphoglucoisomerase
Fructose-6-phosphate
ATP
Phosphofructokinase
ADP
Fructose1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
LE 9-9b_1
2 NAD+
Triose phosphate
dehydrogenase
2 NADH
+ 2 H+
1, 3-Bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
2-Phosphoglycerate
LE 9-9b_2
2 NAD+
Triose phosphate
dehydrogenase
2 NADH
+ 2 H+
1, 3-Bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
2-Phosphoglycerate
2 H2O
Enolase
Phosphoenolpyruvate
2 ADP
Pyruvate kinase
2 ATP
Pyruvate
Concept 9.3: The citric acid cycle completes the
energy-yielding oxidation of organic molecules
• Before the citric acid cycle can begin, pyruvate
must be converted to acetyl CoA, which links
the cycle to glycolysis
MITOCHONDRION
CYTOSOL
NAD+
NADH
+ H+
Acetyl Co A
Pyruvate
CO2
Transport protein
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Coenzyme A
• The citric acid cycle, also called the Krebs cycle,
takes place within the mitochondrial matrix
Pyruvate
(from glycolysis,
2 molecules per glucose)
CO2
NAD+
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
CoA
NADH
+ H+
ATP
Acetyl CoA
CoA
CoA
Citric
acid
cycle
2 CO2
FADH2
3 NAD+
3 NADH
+ 3 H+
FAD
ADP + Pi
ATP
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Animation: Electron Transport
• The citric acid cycle has eight steps, each
catalyzed by a specific enzyme
acetyl CoA + oxaloacetate
citrate
• The next seven steps decompose the citrate back
to oxaloacetate, making the process a cycle
• Electron Carriers:
•
NADH and FADH2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-12_1
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
Acetyl CoA
H2O
Oxaloacetate
Citrate
Isocitrate
Citric
acid
cycle
LE 9-12_2
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
Acetyl CoA
H2O
Oxaloacetate
Citrate
Isocitrate
CO2
Citric
acid
cycle
NAD+
NADH
+ H+
a-Ketoglutarate
NAD+
Succinyl
CoA
NADH
+ H+
CO2
LE 9-12_3
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
Acetyl CoA
H2O
Oxaloacetate
Citrate
Isocitrate
CO2
Citric
acid
cycle
NAD+
NADH
+ H+
Fumarate
a-Ketoglutarate
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
LE 9-12_4
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
Acetyl CoA
NADH
+ H+
H2O
NAD+
Oxaloacetate
Malate
Citrate
Isocitrate
CO2
Citric
acid
cycle
H2O
NAD+
NADH
+ H+
Fumarate
a-Ketoglutarate
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Concept 9.4: 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 cristae of the
mitochondrion
• Most of the chain’s components are proteins
• Electrons drop in free energy as they go down the
chain and are finally passed to O2, forming water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-13
NADH
50
Free energy (G) relative to O2 (kcal/mol)
FADH2
40
FMN
I
Multiprotein
complexes
FAD
Fe•S II
Fe•S
Q
III
Cyt b
30
Fe•S
Cyt c1
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylation:
electron transport
and chemiosmosis
IV
Cyt c
Cyt a
Cyt a3
20
10
0
2 H+ + 1/2 O2
H2O
ATP
Chemiosmosis: The Energy-Coupling Mechanism
• Electron transfer in the ETC causes proteins to
pump H+ from the mitochondrial matrix to the
intermembrane space
• H+ then moves back across the membrane,
passing through channels in ATP synthase
• This is an example of chemiosmosis, the use of
energy in a H+ gradient to drive cellular work
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-15
Inner
mitochondrial
membrane
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP
H+
H+
H+
H+
Intermembrane
space
Cyt c
Protein complex
of electron
carriers
Q
IV
III
I
ATP
synthase
II
Inner
mitochondrial
membrane
FADH2
NADH + H+
2H+ + 1/2 O2
H2O
FAD
NAD+
Mitochondrial
matrix
ATP
ADP + P i
(carrying electrons
from food)
H+
Electron transport chain
Electron transport and pumping of protons (H+),
Which create an H+ gradient across the membrane
Oxidative phosphorylation
Chemiosmosis
ATP synthesis powered by the flow
of H+ back across the membrane
LE 9-14
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
H+
A rotor within
the membrane
spins as shown
when H+ flows
past
it down the H+
gradient.
A stator
anchored in the
membrane
holds the knob
stationary.
H+
ADP
+
Pi
MITOCHONDRAL MATRIX
ATP
A rod (or
“stalk”)
extending into
the knob also
spins,
activating
catalytic sites in
the knob.
Three catalytic
sites in the
stationary knob
join inorganic
phosphate to
ADP to make
ATP.
The H+ gradient is referred to as a proton-motive force,
emphasizing its capacity to do work
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 40% of the energy in a glucose molecule is
transferred to ATP during cellular respiration,
making about 38 ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-16
Electron shuttles
span membrane
CYTOSOL
2 NADH
Glycolysis
Glucose
2
Pyruvate
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2
Acetyl
CoA
6 NADH
Citric
acid
cycle
+ 2 ATP
+ 2 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
About
36 or 38 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by oxidation phosphorylation, depending
on which shuttle transports electrons
form NADH in cytosol
Concept 9.5: Fermentation enables some cells to
produce ATP without the use of oxygen
• Cellular respiration requires O2 to produce ATP
• Glycolysis can produce ATP with or without O2 (in
aerobic or anaerobic conditions)
• In the absence of O2, glycolysis couples with
fermentation to produce 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, with the first releasing CO2
• Alcohol fermentation by yeast is used in brewing,
Play
winemaking, and baking
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LE 9-17a
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 Ethanol
Alcohol fermentation
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
• 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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LE 9-17b
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 CO2
2 Pyruvate
2 Lactate
Lactic acid fermentation
• Yeast and many
bacteria are
facultative
anaerobes, meaning
that they can survive
using either
fermentation or
cellular respiration
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
Ethanol
or
lactate
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O2 present
Cellular respiration
MITOCHONDRIO
Acetyl CoA
Citric
acid
cycle
The Versatility of Catabolism
• Catabolic pathways
funnel electrons from
many kinds of
organic molecules
into cellular
respiration
Proteins
Carbohydrates
Amino
acids
Sugars
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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