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Chapter 9 Cell Respiration Mr. Hunter Hyde Park AcademyTRANSCRIPT
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
PowerPoint Lectures for Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Chapter 9
Cellular Respiration: Harvesting Chemical Energy
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• Overview: Life Is Work
• Living cells
– Require transfusions of energy from outside sources to perform their many tasks
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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
CO2 + H2O
Photosynthesisin chloroplasts
Cellular respiration
in mitochondria
Organicmolecules+ O2
ATP
powers most cellular work
HeatenergyFigure 9.2
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• Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
• These fuels can consists of high energy molecules such as ____________ and ________
• These molecules are rich in Carbon and Hydrogen. The actual energy is found in the bonds of the molecule. Hydrogen atoms provide an excellent source of energy by means of their _________.
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Catabolic Pathways and Production of ATP• The breakdown of organic molecules is exergonic
• All exergonic reactions release ________.
• All endergonic reactions require _________.
• Free energy can be defined as the energy available for a system to perform work when temperature and pressure are constant throughout the system. This environment is present within certain cellular components of the body.
• The quantitative value of free energy (G) in exergonic reactions is always negative because there is a net release of free energy. (-G) In endergonic reactions, since energy is required the free energy would be ______, due to a net gain in free energy.
• The ________ the decrease in free energy, the greater amount of work the reaction can perform.
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• Cellular respiration
– Is the most prevalent and efficient catabolic pathway
– Consumes oxygen and organic molecules such as glucose
– Yields ATP
ATP is the energy currency of the cell.
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• To keep working
– Cells must regenerate _______
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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
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• In oxidation
– A substance loses electrons, or is oxidized
• In reduction
– A substance gains electrons, or is reduced
– The reducing agent is the substance that __________ electrons.
– The oxidizing agent is the substance that ________ the electrons.
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• Examples of redox reactions
Na + Cl Na+ + Cl–
becomes oxidized(loses electron)
becomes reduced(gains electron)
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• Some redox reactions
– Do not completely exchange electrons
– Change the degree of electron sharing in covalent bonds
– The greater the atoms electronegativity, the stronger its pull on electrons.
– _______ has the greatest electronegativity among all the elements.
CH4
H
H
HH
C O O O O OC
H H
Methane(reducingagent)
Oxygen(oxidizingagent)
Carbon dioxide Water
+ 2O2CO
2+ Energy + 2 H2O
becomes oxidized
becomes reduced
Reactants Products
Figure 9.3
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Oxidation of Organic Fuel Molecules During Cellular Respiration• During cellular respiration
– Glucose is oxidized and oxygen is reduced
– The transfer of electrons are in the form of ________ atoms.
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
becomes oxidized
becomes reduced
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Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
• Cellular respiration
– Oxidizes glucose in a series of steps
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• Electrons from organic compounds
– Are usually first transferred to NAD+, a coenzyme
NAD+
H
O
OO O–
OO O–
O
O
O
P
P
CH2
CH2
HO OHH
HHO OH
HO
H
H
N+
C NH2
HN
H
NH2
N
N
Nicotinamide(oxidized form)
NH2+ 2[H](from food)
Dehydrogenase
Reduction of NAD+
Oxidation of NADH
2 e– + 2 H+
2 e– + H+
NADH
OH H
N
C +
Nicotinamide(reduced form)
N
Figure 9.4
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• NADH, the reduced form of NAD+
– Passes the electrons to the electron transport chain
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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
(a) Uncontrolled reaction
Free
ene
rgy,
G
H2O
Explosiverelease of
heat and lightenergy
Figure 9.5 A
H2 + 1/2 O2
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• The electron transport chain
– Passes electrons in a series of steps instead of in one explosive reaction
– Uses the energy from the electron transfer to form ATP
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2 H 1/2 O2
(from food via NADH)
2 H+ + 2 e–
2 H+
2 e–
H2O
1/2 O2
Controlled release of energy for synthesis of
ATP ATP
ATP
ATP
Electron transport chain
Free
ene
rgy,
G
(b) Cellular respiration
+
Figure 9.5 B
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The Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of three metabolic stages
– Glycolysis
– The citric acid cycle
– Oxidative phosphorylation
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• Anaerobic: Without Oxygen
• Aerobic: With Oxygen
• Glycolysis
– Breaks down glucose into two molecules of pyruvate
• The citric acid cycle
– Completes the breakdown of glucose
– It does this when oxygen is not available
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• Oxidative Phosphorylation
– Is driven by the electron transport chain (ETC).
– Generates ATP by transferring an inorganic phosphate to ADP.
– Generates ATP by means of a hydrogen ion gradient.
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• An overview of cellular respiration
Figure 9.6
Electronscarried
via NADH
GlycolsisGlucos
ePyruvate
ATP
Substrate-levelphosphorylation
Electrons carried via NADH and
FADH2
Citric acid cycle
Oxidativephosphorylation:
electron transport and
chemiosmosis
ATPATP
Substrate-levelphosphorylation
Oxidativephosphorylation
MitochondrionCytosol
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• Both glycolysis and the citric acid cycle
– Can generate ATP by _________ level phosphorylation. An inorganic phosphate is added to a substrate. The reaction is enzymatically catalyzed to produce ATP and a product.
Figure 9.7
Enzyme Enzyme
ATP
ADP
Product
SubstrateP
+
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• Concept 9.2: 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
– Energy investment phase
– Energy payoff phase
Glycolysis Citricacidcycle
Oxidativephosphorylation
ATP ATP ATP
2 ATP
4 ATP
used
formed
Glucose
2 ATP + 2 P
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H +
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Energy investment phase
Energy payoff phase
Glucose 2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H +
2 NADH
+ 2 H+
Figure 9.8
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Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
HH
H
HH
OHOH
HO HO
CH2OHH H
H
HO H
OHHO OH
P
CH2O P
H
OH
HO
HO
HHO
CH2OH
P O CH2O CH2 O P
HOH HO
HOH
OP CH2
C OCH2OH
HCCHOHCH2
O
O P
ATP
ADPHexokinase
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
ATP
ADP
Phosphoglucoisomerase
Phosphofructokinase
Fructose-1, 6-bisphosphate
Aldolase
Isomerase
Glycolysis
1
2
3
4
5
CH2OHOxidative
phosphorylation
Citricacidcycle
Figure 9.9 A
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2 NAD+
NADH2+ 2 H+
Triose phosphatedehydrogenase
2 P i
2P C
CHOHO
P
O
CH2 O
2 O–
1, 3-Bisphosphoglycerate2 ADP
2 ATP
Phosphoglycerokinase
CH2 O P
2
CCHOH
3-Phosphoglycerate
Phosphoglyceromutase
O–
CC
CH2OH
H O P
2-Phosphoglycerate
2 H2O
2 O–
Enolase
CC
OPO
CH2Phosphoenolpyruvate
2 ADP
2 ATPPyruvate kinase
O–
C
COO
CH3
2
6
8
7
9
10
Pyruvate
O
Figure 9.8 B
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• Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules
• The citric acid cycle
– Takes place in the ________ of the mitochondrion
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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
NADH + H+NAD+
2
31
CO2 Coenzyme APyruvate
Acetyle CoA
S CoA
C
CH3
O
Transport protein
O–
O
O
C
C
CH3
Figure 9.10
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• An overview of the citric acid cycle
ATP
2 CO2
3 NAD+
3 NADH
+ 3 H+
ADP + P i
FAD
FADH2
Citricacidcycle
CoA
CoA Acetyle CoA
NADH+ 3 H+
CoA
CO2
Pyruvate(from glycolysis,2 molecules per glucose)
ATP ATP ATP
Glycolysis Citricacidcycle
Oxidativephosphorylation
Figure 9.11
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• A closer look at the citric acid cycle
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Figure 9.12
Acetyl CoA
NADH
Oxaloacetate
CitrateMalate
Fumarate
SuccinateSuccinyl
CoA
-Ketoglutarate
Isocitrate
Citricacidcycle
S CoA
CoA SH
NADH
NADH
FADH2
FAD
GTP GDP
NAD+
ADP
P i
NAD+
CO2
CO2
CoA SH
CoA SH
CoAS
H2O
+ H+
+ H+ H2O
C
CH3
O
O C COO–
CH2
COO–
COO–
CH2
HO C COO–
CH2
COO–
COO–
COO–
CH2
HC COO–
HO CHCOO–
CHCH2
COO–
HO
COO–
CH
HC
COO–
COO–
CH2
CH2
COO–
COO–
CH2
CH2
C O
COO–
CH2
CH2
C O
COO–
1
2
3
4
5
6
7
8
Glycolysis Oxidativephosphorylation
NAD+
+ H+
ATP
Citricacidcycle
Figure 9.12
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• Concept 9.4: During oxidative phosphorylation, ____________ 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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• At the end of the chain
– Electrons are passed to oxygen, forming water
– Oxygen has the greatest affinity
– for electrons (electronegative)
H2O
O2
NADH
FADH2
FMNFe•S Fe•S
Fe•S
O
FAD
Cyt b
Cyt c1Cyt c
Cyt aCyt a3
2 H + + 12
III
III
IV
Multiproteincomplexes
0
10
20
30
40
50
Free
ene
rgy
(G) r
elat
ive
to O
2 (k
cl/m
ol)
Figure 9.13
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Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase
– Is the enzyme that actually makes ATPINTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+ H+
H+
P i
+ADP
ATP
A rotor within the membrane spins clockwise whenH+ flows past it down the H+
gradient.
A stator anchoredin the membraneholds the knobstationary.
A rod (for “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob.
Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. MITOCHONDRIAL MATRIXFigure 9.14
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• At certain steps along the electron transport chain (ETC)
– Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space.
– These Hydrogen ions are from the electron carriers _______ and ________ after they become _______.
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• The resulting H+ gradient
– Stores energy
– Drives chemiosmosis in ATP synthase
– Is referred to as a ________-motive force
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• Chemiosmosis
– Is an energy-coupling mechanism that uses ________ in the form of a H+ gradient across a membrane to drive cellular work
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• Chemiosmosis and the electron transport chain
Oxidativephosphorylation.electron transportand chemiosmosis
Glycolysis
ATP ATP ATP
InnerMitochondrialmembrane
H+
H+H+
H+
H+
ATPP i
Protein complexof electron carners
Cyt c
I
II
III
IV
(Carrying electronsfrom, food)
NADH+
FADH2
NAD+
FAD+ 2 H+ + 1/2 O2
H2O
ADP +
Electron transport chainElectron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane
ATPsynthase
Q
Oxidative phosphorylation
Intermembranespace
Innermitochondrialmembrane
Mitochondrialmatrix
Figure 9.15
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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 shuttlesspan membrane
CYTOSOL 2 NADH
2 FADH2
2 NADH 6 NADH 2 FADH22 NADH
Glycolysis
Glucose2
Pyruvate
2AcetylCoA
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
MITOCHONDRION
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol
Maximum per glucose:About
36 or 38 ATP
+ 2 ATP + 2 ATP + about 32 or 34 ATP
or
Figure 9.16
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• About 40% of the energy in a glucose molecule
– Is transferred to ATP during cellular respiration, making approximately 38 ATP
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• Concept 9.5: 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
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• In alcohol fermentation
– Pyruvate is converted to ethanol in two steps, one of which releases CO2
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• During lactic acid fermentation
– Pyruvate is reduced directly to NADH to form lactate as a waste product
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2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH
2 Pyruvate
2 Acetaldehyde 2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 P1 2 ATP
GlycolysisGlucose
2 NAD+ 2 NADH
2 Lactate
(b) Lactic acid fermentation
HH OH
CH3
C
O –
OCC O
CH3
HC O
CH3
O–
C O
C O
CH3OC O
C OHH
CH3
CO22
Figure 9.17
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Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other organic fuels to pyruvate
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• 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 catabolismGlucose
CYTOSOL
PyruvateNo O2 presentFermentation
O2 present Cellular respiration
Ethanolor
lactate
Acetyl CoAMITOCHONDRION
Citricacidcycle
Figure 9.18
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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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• Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways
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The Versatility of Catabolism
• Catabolic pathways
– Funnel electrons from many kinds of organic molecules into cellular respiration
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• The catabolism of various molecules from food
Amino acids
Sugars Glycerol Fattyacids
GlycolysisGlucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citricacidcycle
Oxidativephosphorylation
FatsProteins Carbohydrates
Figure 9.19
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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• Cellular respiration
– Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle
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• The control of cellular respirationGlucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphateInhibits Inhibits
Pyruvate
ATPAcetyl CoA
Citricacidcycle
Citrate
Oxidativephosphorylation
Stimulates
AMP
+– –
Figure 9.20