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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
Life is Work
Living cells
– Require transfusions of energy from outside
sources to perform their many tasks
– Ultimate energy source is SUN
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• The giant panda
– Obtains energy for its cells by eating plants
Figure 9.1
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• Energy
– Flows into an ecosystem as sunlight and
leaves as heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
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Heat
energy
Catabolic Pathways
Catabolic is the breakdown of molecules
Ex. Cellular respiration
breaks down glucose & releases energy
Yields ATP
exergonic reaction (-686 kcal/mol)
*Does not directly move or pump anything
or do other cellular work
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How does a catabolic pathway yield energy?
*By transferring electrons during chemical
reaction.
Relocation of electrons release energy stored
in the bonds of organic molecules.
Uses the principle of REDOX reactions
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The Principle of Redox
• Redox reactions terms
1. Oxidation (LEO)
2. Reduction (GER)
3. Reducing agent (electron donor)
4. Oxidizing agent (electron acceptor)
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• Examples of redox reactions
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
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Cl–
• Some redox reactions
– Do not completely exchange electrons
– Change the degree of electron sharing in
covalent bonds
Products
Reactants
becomes oxidized
+
CH4
CO
2O2
+
Energy
2 H2O
becomes reduced
O
O
C
O
H
O
O
H
H
H
C
+
2
H
H
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Figure 9.3
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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
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Cellular respiration
Oxidizes glucose in a series of steps
Catalyzed by ENZYMES
Electrons travel with hydrogen atom
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• Electrons from organic compounds
– Are usually first transferred to NAD+, a
coenzyme
2 e– + 2 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
O
H
HO
N
H
OH
Reduction of NAD+
+ 2[H]
(from food) Oxidation of NADH
NH2
N
N
2 e– + H+
H
Figure 9.4
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NADH
H O
C
H
N
NH2
Nicotinamide
(reduced form)
+
• NADH, the reduced form of NAD+
– Passes the electrons to the electron transport
chain
– Oxygen is FINAL ELECTRON ACCEPTOR
– * electrons go downhill
(think hill, higher up has more PE)
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• 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
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(a) Uncontrolled reaction
• The electron transport chain (ETS)
– Passes electrons in a series of steps instead of
in one explosive reaction
– NADH used in ETS
– Uses the energy from the electron transfer to
form ATP
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2H
1/
+
2
O2
1/
O2
(from food via NADH)
Free energy, G
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e–
2
H+
H2O
Figure 9.5 B
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(b) Cellular respiration
2
The Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of three
metabolic stages
1. Glycolysis (technically not respiration, but is
included b/c it’s the first step whether oxygen is
present or not)
2. The citric acid cycle
3. Oxidative phosphorylation
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1. Glycolysis (occurs in cytoplasm)
– Breaks down glucose into two molecules of
pyruvate
2. The citric acid cycle (mitochrondrial matrix)
– Completes the breakdown of glucose
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3. Oxidative phosphorylation (occurs in the inner
mitochondria membrane)
a. Is driven by the electron transport chain
b. chemiosmosis
• Generates ATP – 90% of all ATP cell makes
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• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Figure 9.6
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Substrate-level
phosphorylation
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ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
• Both glycolysis and the citric acid cycle
– Can generate ATP by substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Figure 9.7
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Product
ATP
Stages of Cellular Respiration
1. 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
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• Glycolysis consists of two major phases
– A. Energy investment phase
– B. Energy payoff phase
Citric
acid
cycle
Glycolysis
Oxidative
phosphorylation
ATP
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 formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Glucose
4 ATP formed – 2 ATP used
Figure 9.8
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2 NAD+ + 4 e– + 4 H
+
2 Pyruvate + 2 H2O
2 ATP + 2 H+
2 NADH
A. Energy Investment phase
Steps
1. Glu  glu-6-phospate
Hexokinase adds P group
ATP used
2. glu-6-P  fructose-6-P (isomer)
Phosphoglucoisomerase
3. fru-6-P  fru 1,6 bisphosphate
Phosphofructokinase adds P group
ATP used
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4.
Fru 1,6 bisP  dihydroxyacetone or glyceraldehyde-3-P
Aldolase splits into 2 3-C groups (ISOMERS)
5.
ISOMERASE catalyzes rxn btwn two forms
Equilibrium never met b/c next step only uses
glyceraldehyde-3-P
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CH2OH
HH
H
HO H
HO
OH
H OH
Glycolysis
Glucose
ATP
1
Hexokinase
ADP
CH2OH P
HH OH
OH H
HO
H OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
CH2O P
O CH2OH
H HO
HO
H
HO H
Fructose-6-phosphate
ATP
3
Phosphofructokinase
ADP
P O CH2 O CH2 O P
HO
H
OH
HO H
Fructose1, 6-bisphosphate
4
Aldolase
5
H
P O CH2 Isomerase
C O
C O
CHOH
CH2OH
CH2 O P
Figure 9.9 A
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
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Citric
Oxidative
acid
cycle phosphorylation
B. Energy Payoff Phase
6.
Glyceraldehyde-3-P  1,3-biphosphoglycerate
Transfer of electrons & H+ to NAD+
Forms 2 NADH
Triose phosphate dehydrogenase
7.
1,3-biphosphoglycerate  3-phosphoglycerate
Phosphoglycerokinase
2 ATP produced
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•
8. 3-Phosphoglycerate  2-Phosphoglycerate
–
Relocates the P group
–
Phosphoglyceromutase
9.
2-Phosphoglycerate  phosphoenolpyruvate (PEP)
Enolase
2 water molecules released
Molecule has unstable P bond
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• 10. Phosphoenolpyruvate  PYRUVATE
P group goes to ADP
Pyruvate kinase
2 ATP formed
Sum of Glycolysis
2 net ATP
2 NADH
2 pyruvate
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6
Triose phosphate
dehydrogenase
2 NAD+
2 Pi
2 NADH
+ 2 H+
2
P
O C O
CHOH
CH2 O P
1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
O–
2
C
CHOH
CH2 O P
3-Phosphoglycerate
8
Phosphoglyceromutase
2
O–
C
O
H C O
P
CH2OH
2-Phosphoglycerate
9
Enolase
2H O
2
2
O–
C O
C O
P
CH2
Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
O–
C O
C O
Figure 9.8 B
CH3
Pyruvate
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Stages of Cellular Respiration
2.
The citric acid cycle (Kreb’s cycle)
if oxygen present  pryuvate enters the matrix of the
mitochondrion
A. Btwn glycolysis & Krebs:
Pyruvate  Acetyl CoA
1.
Carbon dioxide given off
2.
NADH is formed
3.
CoA added to pyruvate
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• 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
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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
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Citric Acid Cycle
B. Acetyl CoA enters Krebs cycle
8 steps
1. Acetyl CoA adds to oxaloacetate  citrate
2. Citrate  Isocitrate (one water removed, one water
added)
3. Isocitrate  alpha- ketoglutarate
Carbon dioxide given off
NADH formed
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4.
Alpha-ketoglutarate  Succinyl CoA
NADH formed
Carbon dioxide given off
5.
Succinyl CoA  Succinate
ATP formed
6.
Succinate  Fumarate
FADH2 formed
7.
Fumarate  Malate
Water added
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• 8. Malate  Oxaloacetate
–
NADH formed
TOTAL per pyruvate (MULTIPLY BY 2 to get total)
Before enter Kreb’s cycle:
1 NADH
CO2 produced
Krebs cycle:
2 CO2
1 ATP
3 NADH
FADH2
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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
Figure
CH2
HO
Citrate
9.12
COO–
Isocitrate
COO–
H2O
COO–
CH
CO2
Citric
acid
cycle
7
3
NAD+
COO–
Fumarate
HC
CH
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
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4
C O
COO–
CH2
5
CH2
FADH2
COO–
NAD+
NADH
+ H+
+ H+
a-Ketoglutarate
CH2
COO–
NADH
CO2
Oxidative Phosphorylation
• Chemiosmosis couples electron transport to
ATP synthesis
• NADH and FADH2
– Donate electrons to the electron transport
chain, which then powers ATP synthesis
– ATP is not produced directly
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A. Electron Transport Chain
•
Electrons from NADH and FADH2 lose energy
in several steps
•
Located in the folds of inner membrane called
CRISTAE
•
In the cristae, protein complexes I- IV
electrons are transferred
•
Cytochromes – proteins that are electron
carriers w/in complexes
Electron acceptor – O2 (form H2O)
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• 1. At complex I, NADH adds e- at higher level
2. FADH2 at complex II (1/3 less energy for ATP)
NADH
50
Free energy (G) relative to O2 (kcl/mol)
FADH2
40
FMN
I
Fe•S
Fe•S II
O
30
Multiprotein
complexes
FAD
III
Cyt b
Fe•S
20
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
10
0
Figure 9.13
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2 H + + 12 O2
H2 O
B. Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase (enzyme that actually makes ATP)
• Like an ion pump in reverse
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
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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
1. Electron transfer causes protein complexes I-IV
to pump H+ from the mitochondrial matrix to
the intermembrane space
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• 2. The resulting H+ gradient
A. Stores energy
B. Drives chemiosmosis in ATP synthase
C. 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
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• 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
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Oxidative phosphorylation
ATP Production Total
Overall:
Glu  NADH ETS Promotive force  ATP
Glycolysis total:
Citric Acid (2 turns):
2 ATP
2 ATP
2 NADH
6 NADH
30 ATP
2 pyruvate
2 FADH2
4 ATP
2 NADH (before cycle)
Total: 34 ATP
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Ox Phos:
ATP Production
TOTAL (glycolysis, Kreb’s cycle, ox phos)
34 ATP (from ox phos)
4 ATP (substrate phos)
- 2 ATP (active transport, using FADH instead of NADH
before entering Kreb’s cycle)
TOTAL: net 36 ATP OVERALL
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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
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP
Figure 9.16
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Fermentation (lack 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
Two types:
1. Alcohol fermentation (pyruvate to ethanol)
2. Lactic Acid fermentation (pyruvate to lactate)
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1. Alcohol fermentation
Pyruvate converted to ethanol
Two steps:
a. Pyruvate to acetaldehyde (2 carbons)
b. Acetaldehyde reduced by NADH to ethanol
NAD regenerated for glycolysis
CO2 released
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Who does alcohol fermentation?
Bacteria, yeast
Responsible for brewing, winemaking, baking)
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2. Lactic Acid Fermentation
One step:
Pyruvate  lactate (NADH reduced)
No CO2 produced
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Who does lactic acid fermentation?
1. Fungi, bacteria
Makes cheese, yogurt
2. Human muscle cells
lack O2
cause muscle fatigue & pain
lactate goes to liver & converted back to
pyruvate
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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
• 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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• The catabolism of various molecules from food
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Figure 9.19
Oxidative
phosphorylation
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Fatty
acids