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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
Overview: Life Is Work
• Living cells require energy from outside
sources
• Some animals, such as the giant panda, obtain
energy by eating plants; others feed on
organisms that eat plants
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Energy flows into an ecosystem as sunlight
and leaves as heat
• Photosynthesis generates oxygen and organic
molecules, which are used in cellular
respiration
• Cells use chemical energy stored in organic
molecules to regenerate ATP, which powers
work
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
3 Key Pathways of Cellular Respiration
1. Glycolysis
2. Citric Acid Cycle
3. Oxidative Phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 9.1: Catabolic pathways yield energy by
oxidizing organic fuels
A. Catabolic Pathways and Production of ATP
1. The breakdown of organic molecules
is exergonic
2. Fermentation is a partial degradation
of sugars that occurs without oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Catabolic Pathways and Production of ATP
3. Cellular respiration consumes oxygen and
organic molecules and yields ATP
4. Although carbohydrates, fats, and proteins are
all consumed as fuel, it is helpful to trace
cellular respiration with the sugar glucose:
C6H12O6 + 6O2  6CO2 + 6H2O + Energy (ATP + heat)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
B. Redox Reactions: Oxidation and Reduction
1. The transfer of electrons during chemical
reactions releases energy stored in organic
molecules
2. This released energy is ultimately used to
synthesize ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. The Principle of Redox
1. Chemical reactions that transfer electrons
between reactants are called oxidationreduction reactions, or redox reactions
2. Oxidation
a. substance loses electrons
becomes oxidized
(loses electron)
b. is oxidized
Xe-
+
Y
X
+
Ye-
becomes reduced
(gains electron)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. The Principle of Redox
3. Reduction
a. substance gains electrons
b. is reduced (the amount of positive charge is
reduced)
becomes oxidized
(loses electron)
Xe-
+
Y
X
+
Ye-
becomes reduced
(gains electron)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4. The electron donor is called the reducing
agent
5. The electron receptor is called the oxidizing
agent
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
6. Some redox reactions do not transfer
electrons but change the electron sharing in
covalent bonds
• An example is the reaction between methane
and oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
D. Oxidation of Organic Fuel Molecules During
Cellular Respiration
1. During cellular respiration, the fuel (such as
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
D. Oxidation of Organic Fuel Molecules During
Cellular Respiration
2. In general, organic molecules with an
abundance of hydrogen are excellent fuels
because their bonds release energy when
electrons fall down their energy gradient
(usually toward oxygen)
3. Activation energy barrier holds back the flood
of electrons to a lower energy state
a. enzymes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
E. Stepwise Energy Harvest via NAD+ and the
Electron Transport Chain
1. In cellular respiration, glucose and other
organic molecules are broken down in a series
of steps
2. Electrons from organic compounds are
usually first transferred to NAD+
a. coenzyme
b. electron acceptor - functions as an oxidizing
agent during cellular respiration
c. derived from vitamin niacin
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
E. Stepwise Energy Harvest via NAD+ and the
Electron Transport Chain
3. Energy is passed to NADH
a. the reduced form of NAD+
b. NADH passes the electrons to the electron
transport chain
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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+
4. the electron transport chain passes electrons
in a series of steps instead of one explosive
reaction
a. Oxygen pulls electrons down the chain in an
energy-yielding tumble
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
F. Cellular Respiration has three stages
1. Glycolysis (breaks down glucose into two
molecules of pyruvate)
a. A small amount of ATP is formed in glycolysis
by substrate-level phosphorylation
1) substrate-level phosphorylation occurs
when an enzyme transfers a phosphate group
from a substrate molecule to ADP
[Animation listed on slide following figure]
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
F. Cellular Respiration has three stages
2. The citric acid cycle (completes the breakdown of
glucose)
a. a small amount of ATP is formed in citric acid
cycle by substrate-level phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
F. Cellular Respiration has three stages
3. Oxidative phosphorylation (accounts for most of
the ATP synthesis)
a. The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
b. oxidative phosphorylation accounts for almost
90% of the ATP generated by cellular respiration
c. inorganic phosphate is transferred to ADP
[Animation listed on slide following figure]
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-7
Enzyme
Enzyme
ADP
P
Substrate
+
Product
ATP
Concept 9.2: Glycolysis harvests energy by
oxidizing glucose to pyruvate
A. Glycolysis
1. “splitting of sugar”
2. breaks down glucose into two molecules of
pyruvate
3. 2-3 carbon sugars
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 9.2: Glycolysis harvests energy by
oxidizing glucose to pyruvate
B. Glycolysis occurs in the cytoplasm
C. two major phases:
1. Energy investment phase
2. Energy payoff phase
Animation: Glycolysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
A. Before the citric acid cycle can begin,
pyruvate must be converted to acetyl CoA,
which links the cycle to glycolysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-10
MITOCHONDRION
CYTOSOL
NAD+
NADH
+ H+
Acetyl Co A
Pyruvate
Transport protein
CO2
Coenzyme A
B. The citric acid cycle, also called the Krebs
cycle
C. takes place within the mitochondrial matrix
D. The cycle oxidizes organic fuel derived from
pyruvate, generating one ATP, 3 NADH, and 1
FADH2 per turn
Animation: Electron Transport
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-11
Pyruvate
(from glycolysis,
2 molecules per glucose)
CO2
NAD+
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
CoA
NADH
+ H+
Acetyl CoA
CoA
CoA
Citric
acid
cycle
FADH2
2 CO2
3 NAD+
3 NADH
+ 3 H+
FAD
ADP + P i
ATP
ATP
1. The citric acid cycle has eight steps, each
catalyzed by a specific enzyme
2. The acetyl group of acetyl CoA joins the
cycle by combining with oxaloacetate, forming
citrate
3. The next seven steps decompose the citrate
back to oxaloacetate, making the process a
cycle
4. The NADH and FADH2 produced by the cycle
relay electrons extracted from food to the
electron transport chain
E. Each glucose causes two turns of the cycle
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
A. Following glycolysis and the citric acid cycle,
NADH and FADH2 account for most of the
energy extracted from food
B. These two electron carriers donate electrons
to the electron transport chain, which powers
ATP synthesis via oxidative phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
C. The Pathway of Electron Transport
1. The electron transport chain is in the cristae of
the mitochondrion
2. Most of the chain’s components are proteins,
which exist in multiprotein complexes
3. The carriers alternate reduced and oxidized
states as they accept and donate electrons
4. 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
5. The electron transport chain generates no ATP
6. The chain’s function is to break the large freeenergy drop from food to O2 into smaller steps
that release energy in manageable amounts
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
D. Chemiosmosis: The Energy-Coupling
Mechanism
1. Electron transfer in the electron transport
chain causes proteins to pump H+ from the
mitochondrial matrix to the intermembrane
space
2. H+ then moves back across the membrane,
passing through channels in ATP synthase
3. 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-14
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
as shown when
H+ flows past
it down the H+
gradient.
H+
A stator anchored
in the membrane
holds the knob
stationary.
A rod (or “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
H+
ADP
+
P
ATP
i
MITOCHONDRAL MATRIX
Three catalytic
sites in the
stationary knob
join inorganic
phosphate to
ADP to make
ATP.
4. The energy stored in a H+ gradient across a
membrane couples the redox reactions of the
electron transport chain to ATP synthesis
5. The H+ gradient is referred to as a protonmotive force
a. emphasizing its capacity to do work
b. the force drives H+ back across the
membrane through H+ channels
Animation: Fermentation Overview
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
E. An Accounting of ATP Production by Cellular
Respiration
1. During cellular respiration, most energy flows
in this sequence:
glucose NADH electron transport chain
proton-motive force ATP
2. 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
A. Cellular respiration requires O2 to produce
ATP
B. Glycolysis can produce ATP with or without
O2 (in aerobic or anaerobic conditions)
C. In the absence of O2, glycolysis couples with
fermentation to produce ATP
D. Fermentation consists of glycolysis plus
reactions that regenerate NAD+, which can be
reused by glycolysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
E. Two common types of fermentation
1. alcoholic fermentation
a. pyruvate is converted to ethanol in two
steps, with the first releasing CO2
b. Alcohol fermentation by yeast is used in
brewing, winemaking, and baking
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
2. Lactic acid fermentation
a. pyruvate is reduced to NADH, forming
lactate as an end product, with no release of
CO2
b. 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
F. Fermentation and Cellular Respiration
Compared
1. Both processes use glycolysis to oxidize
glucose and other organic fuels to pyruvate
2. The processes have different final electron
acceptors: an organic molecule (such as
pyruvate) in fermentation and O2 in cellular
respiration
3. Cellular respiration produces much more ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
4. 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-18
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
G. The Evolutionary Significance of Glycolysis
1. Glycolysis occurs in nearly all organisms
2. Glycolysis probably evolved in ancient
prokaryotes before there was oxygen in the
atmosphere
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 9.6: Glycolysis and the citric acid cycle
connect to many other metabolic pathways
A. Gycolysis and the citric acid cycle are major
intersections to various catabolic and anabolic
pathways
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
B. The Versatility of Catabolism
1. Catabolic pathways funnel electrons from
many kinds of organic molecules into cellular
respiration
2. Glycolysis accepts a wide range of
carbohydrates
3. Proteins must be digested to amino acids;
amino groups can feed glycolysis or the citric
acid cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
B. The Versatility of Catabolism
4. Fats are digested to glycerol (used in
glycolysis) and fatty acids (used in generating
acetyl CoA)
a. An oxidized gram of fat produces more than
twice as much ATP as an oxidized gram of
carbohydrate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-19
Proteins
Carbohydrates
Amino
acids
Sugars
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Fats
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
C. Biosynthesis (Anabolic Pathways)
1. The body uses small molecules to build other
substances
2. These small molecules may come directly
from food, from glycolysis, or from the citric
acid cycle
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
D. Regulation of Cellular Respiration via Feedback
Mechanisms
1. Feedback inhibition is the most common
mechanism for control
2. If ATP concentration begins to drop,
respiration speeds up; when there is plenty of
ATP, respiration slows down
3. Control of catabolism is based mainly on
regulating the activity of enzymes at strategic
points in the catabolic pathway
** the energy that keeps us alive is released, not
produced by cellular respiration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 9-20
Glucose
AMP
Glycolysis
Fructose-6-phosphate
–
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation