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Chapter 6
How Cells Harvest Chemical Energy
PowerPoint Lectures for
Campbell Biology: Concepts & Connections, Seventh Edition
Reece, Taylor, Simon, and Dickey
© 2012 Pearson Education, Inc.
Lecture by Edward J. Zalisko
Figure 6.0_1
Chapter 6: Big Ideas
Cellular Respiration:
Aerobic Harvesting
of Energy
Fermentation: Anaerobic
Harvesting of Energy
Stages of Cellular
Respiration
Connections Between
Metabolic Pathways
CELLULAR RESPIRATION:
AEROBIC HARVESTING
OF ENERGY
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Figure 6.1_1
Sunlight energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2
Glucose
H2O
O2
Cellular respiration
in mitochondria
(for cellular
work)
ATP
Heat energy
Cellular Respiration
 Summary Equation:
C6H12O6
6
Glucose
Oxygen
O2
6 CO2
Carbon
dioxide
6
H2O
ATP
Water
 Heat
 Cellular respiration is an exergonic process
 Transfers energy from the bonds in glucose to form
ATP.
 produces up to 32 ATP molecules from each
glucose molecule
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Figure 6.2_1
O2
Breathing
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
Cellular Respiration
Glucose  O2
CO2  H2O  ATP
Figure 4.13
Mitochondrion
Outer
membrane
Intermembrane
space
Inner
membrane
Cristae
Matrix
Cellular Respiration is a Redox Process
Loss of hydrogen atoms
(becomes oxidized)
C6H12O6
6 O2
6 CO2
6 H2O
Glucose
Gain of hydrogen atoms
(becomes reduced)
ATP
 Heat
 Electrons from glucose are slowly harvested and
transferred to two different electron carriers:
– NAD+ and FAD
– NAD+ reduced to NADH; FAD reduced to FADH2
 These electrons are then used to generate ATP by and
electron transport chain and chemiosmosis
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Figure 6.5B
Becomes oxidized
2H
Becomes reduced
NAD
2H
2 H
NADH
2
(carries
2 electrons)
H
Figure 6.5C
NADH
NAD
ATP
2
Controlled
release of
energy for
synthesis
of ATP
H
2
1 O
2 2
2 H
H 2O
STAGES OF CELLULAR
RESPIRATION
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Cellular respiration occurs in three main stages
 Stage 1 – Glycolysis
– Cytoplasm
– Converts glucose to pyruvate
 Stage 2 – Pyruvate oxidation and citric acid cycle
– Mitochondrial matrix
– Pyruvate oxidation: oxidizes pyruvate to acetyl-CoA; generates
NADH
– TCA: acetyl-CoA oxidized to CO2; generates NADH and FADH2
 Stage 3 – Oxidative phosphorylation (pay-off phase)
– Inner membrane of mitochondria
– Produces ATP by chemiosmosis
© 2012 Pearson Education, Inc.
Figure 6.6
CYTOPLASM
NADH
Electrons
carried by NADH
NADH
Glycolysis
Glucose
Pyruvate
Pyruvate
Oxidation
Citric Acid
Cycle
FADH2
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
Mitochondrion
ATP
Substrate-level
phosphorylation
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
Stage 1: Glycolysis occurs in the CYTOPLASM
1 Glucose + 2 ATP + 2 NAD+ + 4 ADP + 4 P
2 Pyruvate + 2 ADP + 2 P + 2 NADH + 4 ATP
 Net Gain: 2 ATP, 2 NADH, 2 Pyruvate
 NO O2 required - Anaerobic process
 NO CO2 yet released - All carbons from original
glucose still accounted for
 All living organisms able to use glycolysis stage to
gain 2 ATP from glucose!!
© 2012 Pearson Education, Inc.
Figure 6.7Ca_s2
Steps 1 – 3 A fuel
molecule is energized,
using ATP.
Glucose
ATP
Step
ENERGY
INVESTMENT
PHASE
1
ADP
P
Glucose 6-phosphate
P
Fructose 6-phosphate
P
Fructose
1,6-bisphosphate
2
ATP
3
ADP
Step 4 A six-carbon
intermediate splits
into two three-carbon
intermediates.
P
4
P
P
Glyceraldehyde
3-phosphate (G3P)
Figure 6.7Cb_s2
Step 5
A redox reaction
generates NADH.
NAD
NAD
5
P
NADH
5
P
NADH
H
H
P
P
P
ADP
Steps 6 – 9
ATP and pyruvate
are produced.
ENERGY
PAYOFF
PHASE
P
P
P
1,3-Bisphosphoglycerate
P
3-Phosphoglycerate
ADP
6
6
ATP
ATP
P
7
7
P
P
2-Phosphoglycerate
8
H2O
P
P
ADP
Phosphoenolpyruvate (PEP)
ADP
9
9
ATP
8
H2O
ATP
Pyruvate
Figure 6.7A
Glucose
2 ADP
2 NAD
2 P
–Direct transfer of P from
one molecule to ADP
2 NADH
2
ATP is formed in
glycolysis by substratelevel phosphorylation
during which
ATP
2 Pyruvate
2 H
Figure 6.6_1
CYTOPLASM
NADH
Electrons
carried by NADH
NADH
Glycolysis
Pyruvate
Glucose
Pyruvate
Oxidation
Citric Acid
Cycle
FADH2
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
Mitochondrion
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Stage 2: Pyruvate Oxidation and The Citric Acid
Cycle Occurs in the mitochondrial matrix
 Pyruvate Oxidation
– The pyruvate formed in glycolysis is transported from the
cytoplasm into mitochondrial matrix (NOTE: Only IF O2 present)
– Two molecules of pyruvate are produced for each molecule of
glucose that enters glycolysis.
NAD
NADH
H
2
CoA
Pyruvate
Acetyl coenzyme A
1
CO2
3
Coenzyme A
Stage 2: Carbons Enter TCA cycle As AcetylCoA
 For each acetyl-CoA that enters the TCA cycle:
– the two-carbon group of acetyl CoA is added to a fourcarbon compound called oxaloacetate, forming citrate
– citrate is degraded back to the four-carbon compound,
– two CO2 are released, and
– 1 ATP, 3 NADH, and 1 FADH2 are produced.
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Figure 6.9A
Acetyl CoA
CoA
CoA
2 CO2
Citric Acid Cycle
3 NAD
FADH2
3 NADH
FAD
3 H
ATP
ADP
P
Figure 6.9B_s1
Acetyl CoA
CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citric Acid Cycle
Step 1
Acetyl CoA stokes
the furnace.
Figure 6.9B_s2
Acetyl CoA
CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citrate
NAD
NADH
2
H
Citric Acid Cycle
CO2 leaves cycle
Alpha-ketoglutarate
3
CO2 leaves cycle
NAD
ADP
Step 1
Acetyl CoA stokes
the furnace.
P
Steps 2 – 3
ATP
NADH, ATP, and CO2
are generated during redox reactions.
NADH
H
Figure 6.9B_s3
Acetyl CoA
CoA
CoA
2 carbons enter cycle
Oxaloacetate
1
Citrate
NADH
H
NAD
5
NAD
NADH
2
H
Citric Acid Cycle
CO2 leaves cycle
Malate
FADH2
Alpha-ketoglutarate
4
3
FAD
CO2 leaves cycle
NAD
Succinate
ADP
Step 1
Acetyl CoA stokes
the furnace.
P
Steps 2 – 3
ATP
NADH, ATP, and CO2
are generated during redox reactions.
NADH
H
Steps 4 – 5
Further redox reactions generate
FADH2 and more NADH.
Energy Accounting (per glucose)
 Glycolysis: 2 NADH; 2 ATP
 Pyruvate oxidation: 2 NADH
 TCA: 2 ATP, 6 NADH, and 2 FADH2.
 Sum Total:
– 4 ATP
– 10 NADH
– 2 FADH2
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Stage 3: Oxidative Phosphorylation uses
electron transport chain and ATP synthase
embedded in inner membrane
 Stage 3: Oxidative phosphorylation (ETC)
– Pay-off phase!! (Get 28 ATPs)
– Electrons carried by NADH and FADH2 are deposited
into ETC to generate ATP by chemiosmosis.
– Each NADH = 2.5 ATPs (x10 = 25 ATP)
– Each FADH2 = 1.5 ATPs (x2 = 3 ATP)
– O2 required as final electron acceptor!!!!
© 2012 Pearson Education, Inc.
6.10 Most ATP production occurs by oxidative
phosphorylation
 Electrons from NADH and FADH2 travel down the
electron transport chain to O2.
 Oxygen picks up H+ to form water.
 Energy released by these redox reactions is used
to pump H+ from the mitochondrial matrix into the
intermembrane space.
 In chemiosmosis, the H+ diffuses back across the
inner membrane through ATP synthase
complexes, driving the synthesis of ATP.
© 2012 Pearson Education, Inc.
Figure 6.10
H
Intermembrane
space
H
H
H
H Mobile
electron
carriers
Protein
complex
of electron
carriers
H ATP
synthase
IV
I
II
FADH2
Electron
flow
NADH
Mitochondrial
matrix
H
H
III
Inner mitochondrial
membrane
H
NAD
FAD
2 H
1
2 O2
H2O
H
ADP
P
ATP
H
Electron Transport Chain
Oxidative Phosphorylation
Chemiosmosis
Figure 6.11
Rotenone
Cyanide,
carbon monoxide
H
H
H
Oligomycin
ATP
synthase
H
H H H
DNP
FADH2
NAD
NADH
FAD
1
O
2 2
2 H
H
H2O
ADP
P
ATP
Figure 6.12
CYTOPLASM
Electron shuttles
across membrane
2 NADH
Mitochondrion
2 NADH
or
2 FADH2
6 NADH
2 NADH
Glycolysis
2
Pyruvate
Glucose
Pyruvate
Oxidation
2 Acetyl
CoA
Citric Acid
Cycle
2 FADH2
Oxidative
Phosphorylation
(electron transport
and chemiosmosis)
Maximum
per glucose:
2
ATP
by substrate-level
phosphorylation
2
ATP
by substrate-level
phosphorylation
 about
28 ATP
by oxidative
phosphorylation
About
32 ATP