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鄭智美
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PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
細胞呼吸: 能量的產生
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Key Concepts
• Catabolic Pathways yield energy by oxidizing organic fuel
• Glycolysis harvests chemical energy by oxidizing glucose
to pyruvate
• The citric Acid cycle completes the energy yielding
oxidation of organic molecules
• Chemiosmosis couples electron transport to ATP synthesis
• Fermentation enables some cels to produce ATP without
the use of oxygen
• Glycolysis and citric acid cycle connect to many other
metabolic pathways
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Life Is Work
• Living cells
– Require transfusions of energy from outside
sources to perform their many tasks
– Obtains energy
for its cells by
eating plants
Figure 9.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energy flow and Chemical Recycling
• Energy
– Flows into an ecosystem as sunlight and leaves as
heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts Organic
CO2 + H2O
+O
Cellular
molecules 2
respiration
in mitochondria
AT
P
powers most cellular work
Figure 9.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Heat
energ
y
Catabolic pathways yield energy by oxidizing
organic fuels
• The breakdown of organic molecules is
exergonic
Organic compound+ O2→CO2+ H2O+Energy
• To keep working
– Cells must regenerate ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Catabolic Pathways and Production of ATP
• fermentation
– Is a partial degradation of sugars that
occurs without oxygen
• Cellular respiration
– Is the most prevalent and efficient catabolic
pathway
– Consumes oxygen and organic molecules
such as glucose
– Yields ATP
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Redox Reactions: Oxidation and Reduction
• Catabolic pathways yield energy
– Due to the transfer of electrons
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The Principle of Redox
• Redox reactions
– Transfer electrons from one reactant to another by
oxidation and reduction
• In oxidation
– A substance loses electrons, or is oxidized
• In reduction
– A substance gains electrons, or is reduced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Examples of redox reactions
becomes oxidized
(loses electron)
Na
+
Cl
Na+
becomes
reduced
(gains
electron)
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+
Cl–
Methane combustion as an energy yielding redox
reaction
• Some redox reactions
– Do not completely exchange electrons
– Change the degree of electron sharing in covalent
bonds
Products
Reactants
becomes
oxidized
+
CH4
2O2
+ 2 H2O
Energy
becomes reduced
O
O
C
O
H
O
O
H
H
H
C
+
CO2
H
H
Methane
(reducing
agent)
Figure 9.3
Oxygen
(oxidizing
agent)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Carbon dioxide
Water
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration
– Glucose is oxidized and oxygen is reduced
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
• Cellular respiration
– Oxidizes glucose in a series of steps
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
NAD+ as an electron shuttle
• Electrons from organic compounds
– Are usually first transferred to NAD+, a coenzyme
2 e– + 2 H+
2 e– + H+
NAD+
Dehydrogenase
O
NH2
H
C
CH2
O
O–
O
O P
O
H
–
O P O HO
O
N+ Nicotinamide
(oxidized form)
H
OH
HO
CH2
N
H
HO
N
H
OH
•
NH2
N
H
O
Reduction of NAD+
+ 2[H]
(from food) Oxidation of NADH
N
Figure 9.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H O
C
H
N
NH2
+
Nicotinamide
(reduced form)
NADH, the reduced form of
NAD+
–
H
NADH
Passes the electrons to
the electron transport
chain
The Uncontrolled Exergonic Reaction
• If electron transfer is not stepwise
– A large release of energy occurs
– As in the reaction of hydrogen and oxygen to form
water
Free energy, G
H2 + 1/2 O2
Figure 9.5 A
Explosive
release of
heat and light
energy
H2O
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(a) Uncontrolled reaction
Cellulae Respiration
2H
• The electron
transport chain
2 H+ + 2 e–
– Uses the energy
from the electron
transfer to form
ATP
O2
Controlled
release of
energy for
synthesis of
ATP
1/
O2
ATP
ATP
ATP
2 e–
2
H+
H2O
Figure 9.5 B
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2
(from food via NADH)
Free energy, G
– Passes electrons
in a series of steps
instead of in one
explosive reaction
1/
+
(b) Cellular respiration
2
The Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of
three metabolic stages
– Glycolysis
Breaks down glucose into two molecules of
pyruvate
– The citric acid cycle
Completes the breakdown of glucose
– Oxidative phosphorylation
Is driven by the electron transport chain
Generates ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
gure 9.6
Substrate-level
phosphorylation
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
ATP
Substrate-level
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ATP
Oxidative
phosphorylation
Substrate Level Phosphorylation
• Both glycolysis and the citric acid cycle
– Can generate ATP by substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Figure 9.7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Product
ATP
Glycolysis harvests energy by oxidizing glucose to
pyruvate
• Glycolysis
– Means “splitting of sugar”
– Breaks down glucose into pyruvate
– Occurs in the cytoplasm of the cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energy Input and Output of Glycolysis
• Glycolysis consists of two major phases
– Energy investment phase
– Energy payoff phase
Citric
acid
cycle
Glycolysis
ATP
Oxidative
phosphorylation
ATP
ATP
Energy investment phase
Glucose
2 ATP + 2
P
2 ATP
used
Energy payoff phase
4 ADP + 4
P
2 NAD+ + 4 e- + 4 H +
4 ATP
2 NADH
formed
+ 2 H+
2 Pyruvate + 2 H2O
Glucose
4 ATP formed – 2 ATP used
Figure 9.8
2 NAD+ + 4 e– + 4 H +
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 Pyruvate + 2 H2O
2 ATP
+ 2 H+
2 NADH
A closer look at the energy investment phase
CH2OH
H H
H
HO H
HO
OH
H
OH
Glycolysis
Glucose
ATP
1
Hexokinase
ADP
CH2OH
P
O H
H H
OH H
HO
H
OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
CH2O
P
O
HO
H
H
CH2OH
HO
H
HO
Fructose-6-phosphate
3
ATP
Phosphofructokinase
ADP
P
O
CH2
O
CH2
HO
H
OH
H
HO
O
Fructose1, 6-bisphosphate
P
4
Aldolase
5
P
Figure 9.9 A
O
CH2
O
C
CH2OH
Dihydroxyacetone
phosphate
Isomerase
H
C
O
CHOH
CH2 O
Glyceraldehyde3-phosphate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
P
Citric
acid
cycle
Oxidative
phosphorylation
A closer look at the energy payoff phase
6
Triose phosphate
dehydrogenase
2 NAD+
2
2
P
Pi
2
NADH
+ 2 H+
O
C
O
CHOH
P
CH2
O
1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
O–
2
C
CHOH
O
CH2
3-Phosphoglycerate
8
P
Phosphoglyceromutase
O–
2
C
H
2 H2 O
2
O
C
O
P
CH2OH
2-Phosphoglycerate
9
Enolase
O–
C
O
C
O
P
CH2
Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
Figure 9.8 B
O–
C
O
C
O
CH3
Pyruvate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The citric acid cycle completes the energy-yielding
oxidation of organic molecules
The citric acid cycle
– Takes place in the matrix of the mitochondrion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Conversion of pyruvate to Acetyl CoA, the junction
beween glycolysis and the citric acid cycle
• Before the citric acid cycle can begin
– Pyruvate must first be converted to acetyl CoA,
which links the cycle to glycolysis
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
O–
S
CoA
C
O
2
C
C
O
O
1
3
CH3
Pyruvate
Transport protein
Figure 9.10
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH3
Acetyle CoA
CO2
Coenzyme A
An overview of the citric acid cycle
Pyruvate
(from glycolysis,
2 molecules per glucose)
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
CoA
NADH
+ 3 H+ Acetyle CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD+
FADH2
FAD
3 NADH
+ 3 H+
ADP + P i
ATP
Figure 9.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
A closer look at the citric acid cycle
Glycolysis
Citric
Oxidative
acid phosphorylation
cycle
S
CoA
C
O
CH3
Acetyl CoA
CoA SH
O
NADH
+ H+
C COO–
COO–
1
CH2
COO–
NAD+
8 Oxaloacetate
HO C
COO–
COO–
CH2
COO–
HO CH
H2O
CH2
CH2
2
HC COO–
COO–
Malate
HO
Citrate
CH2
COO–
Isocitrate
COO–
H2O
CH
7
COO–
CH
CO2
Citric
acid
cycle
3
NAD+
COO–
Fumarate
HC
CH2
CoA SH
6
CoA SH
COO–
FAD
CH2
CH2
COO–
C O
Succinate
Pi
S
CoA
GTP GDP Succinyl
CoA
ADP
ATP
Figure 9.12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4
C O
COO–
CH2
5
CH2
FADH2
COO–
NAD+
NADH
+ H+
+ H+
a-Ketoglutarate
CH2
COO–
NADH
CO2
During oxidative phosphorylation,
chemiosmosis couples electron transport to
ATP synthesis
NADH and FADH2
– Donate electrons to the electron transport chain,
which powers ATP synthesis via oxidative
phosphorylation
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The Pathway of Electron Transport
• In the electron transport chain
– Electrons from NADH and FADH2 lose
energy in several steps
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Free Energy Change During Electron Transport
• At the end of the chain
– Electrons are passed to oxygen, forming water
NADH
50
Free energy (G) relative to O2 (kcl/mol)
FADH2
40
I
FMN
Multiprotein
complexes
FAD
Fe•S
Fe•S
II
O
III
Cyt b
30
Fe•S
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
20
10
0
Figure 9.13
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 H + + 12
O2
H2 O
Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase
– Is the enzyme that actually makes ATP
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
clockwise when
H+ flows past
it down the H+
gradient.
A stator anchored
in the membrane
holds the knob
stationary.
H+
ADP
+
Pi
Figure 9.14
MITOCHONDRIAL MATRIX
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ATP
A rod (for “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.
At certain steps along the electron transport chain

Electron transfer causes protein complexes
to pump H+ from the mitochondrial matrix
to the intermembrane space
• The resulting H+ gradient
– Stores energy
– Drives chemiosmosis in ATP synthase
– Is referred to as a proton-motive force
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Chemiosmosis
– Is an energy-coupling mechanism that uses
energy in the form of a H+ gradient across a
membrane to drive cellular work
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chemiosmosis and the electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane
ATP
ATP
H+
H+
H+
Intermembrane
space
Protein complex
of electron
carners
Q
I
Inner
mitochondrial
membrane
IV
III
ATP
synthase
II
FADH2
NADH+
Mitochondrial
matrix
H+
Cyt c
FAD+
NAD+
2 H+ + 1/2 O2
H2O
ADP +
(Carrying electrons
from, food)
ATP
Pi
H+
Chemiosmosis
Electron transport chain
+
ATP
synthesis
powered by the flow
Electron transport and pumping of protons (H ),
+
+
which create an H gradient across the membrane Of H back across the membrane
Figure 9.15
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidative phosphorylation
An Accounting of ATP Production by Cellular
Respiration
• During respiration, most energy flows in
this sequence
– Glucose to NADH to electron transport
chain to proton-motive force to ATP
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There are three main processes in this metabolic
enterprise
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
6 NADH
Citric
acid
cycle
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
+ 2 ATP
by substrate-level
phosphorylation
About
36 or 38 ATP
Figure 9.16
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2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by oxidative phosphorylation, depending
on which shuttle transports electrons
from NADH in cytosol
Accounting of ATP production by cellular respiration
• About 40% of the energy in a glucose molecule
– Is transferred to ATP during cellular respiration,
making approximately 38 ATP
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Fermentation enables some cells to produce ATP
without the use of oxygen
• Cellular respiration
– Relies on oxygen to produce ATP
• In the absence of oxygen
– Cells can still produce ATP through fermentation
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Glycolysis
– Can produce ATP with or without oxygen, in
aerobic or anaerobic conditions
– 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 glyocolysis
• In alcohol fermentation
– Pyruvate is converted to ethanol in two steps, one
of which releases CO2
• In lactic acid fermentation
– Pyruvate is reduced directly to NADH to form lactate
as a waste product
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Fermentation
2 ADP + 2
P1
2 ATP
O–
C O
Glucose
Glycolysis
C O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
2 CO2
H
H C OH
C O
CH3
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
2 ATP
Glycolysis
O–
C O
C O
O
2 NAD+
2 NADH
C O
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
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CH3
Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
• Fermentation and cellular respiration
– Differ in their final electron acceptor
• Cellular respiration
– Produces more ATP
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Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
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Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in nearly all organisms
– Probably evolved in ancient prokaryotes
before there was oxygen in the atmosphere
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Glycolysis and the citric acid cycle connect to many
other metabolic pathways
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The catabolism of various molecules from food
Proteins
• Catabolic pathways
Amino
acids
– Funnel electrons from
many kinds of organic
molecules into cellular
respiration
Carbohydrates
Sugars
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Figure 9.19
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Oxidative
phosphorylation
Fats
Glycerol
Fatty
acids
Biosynthesis (Anabolic Pathways)
• The body
– Uses small molecules to build other substances
• These small molecules
– May come directly from food or through glycolysis
or the citric acid cycle
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Regulation of Cellular Respiration via Feedback
Mechanisms
Glucose
Glycolysis
• Cellular respiration
– Is controlled by
allosteric enzymes at
key points in
glycolysis and the
citric acid cycle
Fructose-6-phosphate
–
Inhibits
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
Citrate
ATP
Acetyl CoA
Citric
acid
cycle
Figure 9.20
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AMP
Oxidative
phosphorylation