7.1 overview of cellular · pdf file8/30/2013 3 7 phases of cellular respiration •...
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7.1 Overview of Cellular
Respiration• Cellular respiration is the release of energy from
molecules such as glucose accompanied by the
use of this energy to synthesize ATP molecules.
– Aerobic – requires O2
– Gives off CO2
ATP36-38P
glucose water
C6H12O6 + 6O2
oxygen
6CO2 + 6H2O
ADP +
carbondioxide
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3
7.1 Overview of Cellular
Respiration
• Glucose is a high-energy molecule, and as it is broken down, energy is released.
• This energy used to produce ATP.
• The breakdown of one glucose molecule
results in 36 or 38 ATP molecules.
• The pathways of cellular respiration allow the
energy within a glucose molecule to be released slowly for ATP synthesis.
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NAD+ and FAD
• Cellular respiration involves many individual
reactions, each requiring its own enzyme.
– Certain enzymes utilize two coenzymes.
• NAD+ (nicotinamide adenine dinucleotide)
• FAD (flavin adenine dinucleotide)
– Each carries two electrons and two hydrogen
atoms.
– They pick up electrons at specific enzymatic
reactions and carry these electrons to the electron
transport chain.
5
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NAD+
2H
oxidationreduction
2H
2e– + 2H+
NADH + H+
2e– + 2H+
Figure 7.1
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Phases of Cellular Respiration
• Phases of Cellular Respiration
– Glycolysis
– Preparatory Reaction
– Citric Acid Cycle
– Electron Transport Chain
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7
Phases of Cellular Respiration
• Glycolysis is the breakdown of glucose
into two molecules of pyruvate.
– Oxidation by removal of electrons (e-) and hydrogen ions (H+) provides the energy for the immediate buildup of two ATP.
8
Phases of Cellular Respiration
• Preparatory (Prep) Reaction
– Pyruvate is oxidized to acetyl CoA and carbon
dioxide is removed
– One three-carbon molecule becomes one two-carbon molecule.
– Prep reaction occurs twice because glycolysis produces two pyruvates.
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Phases of Cellular Respiration
• Citric Acid Cycle
– Cyclical series of oxidation reactions that
produce one ATP and carbon dioxide per turn
• Acetyl CoA is converted to citric acid and enters the cycle.
• Citric acid cycle turns twice because two acetyl CoA’s are produced per glucose.
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Phases of Cellular Respiration
• Electron Transport Chain
– Series of electron carrier molecules
• Electrons are passed from one carrier to another.
• As the electrons move from a higher energy state to a lower one, energy is released to make ATP.
• Under aerobic conditions 32-34 ATP per glucose molecule can be produced.
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e–
ATP
energy for
synthesis of
e–
electron
transport chain
high-energy
electrons
low-energy
electrons
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Figure 7.3
12Figure 7.2
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e–
e–
e–
e– Mitochondrion
2 ATP
2 ADP
4 ATP total4 ADP
ATP net gain 2 ADP ATP 32 or 34 ADP 32 or 34 ATP
pyruvateglucose
Glycolysis
Cytoplasm
Preparatory reaction Citric acidcycle
Electron transportchain and
chemiosmosis
e–
e–
NADH
NADH
NADH andFADH2
e–
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Phases of Cellular Respiration
• Pyruvate
– Pivotal metabolite in cellular respiration
• If no oxygen is available, pyruvate is reduced to
lactate (in animals) or alcohol and carbon dioxide (in
plants) in a process called fermentation.
• Fermentation results in a net gain of two
ATP/glucose.
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7.2 Outside the Mitochondria:
Glycolysis
• Glycolysis is the breakdown of glucose
to two molecules of pyruvate.
– Takes place in the cytoplasm
– Does not require oxygen
– Transforms one 6-carbon molecule into two
3-carbon molecules
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7.2 Outside the Mitochondria:
Glycolysis• Energy Investment Steps
– Two molecules of ATP used to activate
glucose as glycolysis begins
• Energy Harvesting Steps
– Oxidation of G3P results in NADH synthesis
– Additional chemical changes lead to direct
substrate-level phosphorylation, formation of 4 ATP
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e–
e–
e–
e– Mitochondrion
2 ATP
2 ADP
4 ATP total4 ADP
ATP net gain 2 ADP ATP 32 or 34 ADP 32 or 34 ATP
pyruvateglucose
Glycolysis
Cytoplasm
Preparatory reaction Citric acidcycle
Electron transportchain and
chemiosmosis
e–
e–
NADH
NADH
NADH andFADH2
e–
17
Inputs and Outputs of Glycolysis
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Glycolysis
outputsinputs
2 NAD+
2 ATP
P
2 ATP Net gain
totalATP
2 (3C) pyruvate
NADH
ADP2
2
4
6C glucose
4ADP + 4
18
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ADPADP
StepsEnergy-Investment Steps
- 2 ATPATP ATP 1. Two ATP are used
to activate glucose.
glucose
PP
Figure 7.4
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ADPADP
StepsEnergy-Investment Steps
- 2 ATPATP ATP 1. Two ATP are used
to activate glucose.
2. A resulting C6 molecule breaksdown into 2 C3 molecules.
glucose
P
G3P
P
G3P
PP
Figure 7.4
20
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glucose
PP
ADPADP
Steps
NAD+NAD+
PP
P
P P
P
NADH + H+
P P
Energy-Investment Steps
- 2
NADH + H+
Energy-Harvesting Steps
ATPATP ATP 1. Two ATP are used
to activate glucose.
2. A resulting C6 molecule breaksdown into 2 C3 molecules.
3. NAD+ takes an electronbecoming NADH + H+, withaddition of a second phosphateto the sugar.
BPGBPG
G3P G3P
Figure 7.4
21
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glucose
PP
ADPADP
Steps
+ 2
NAD+
3PG3PG
NAD+
PP
P
P P
ADPADP
P
NADH + H+
P P
P P
Energy-Investment Steps
- 2
ATP
ATP ATP
NADH + H+
Energy-Harvesting Steps
ATPATP ATP 1. Two ATP are used
to activate glucose.
2. A resulting C6 molecule breaksdown into 2 C3 molecules.
3. NAD+ takes an electronbecoming NADH + H+, withaddition of a second phosphateto the sugar.
4. Removal of high-energyphosphate from 2 BPG by 2 ADPproduces 2 ATP and 2 3PGmolecules.
BPGBPG
G3P G3P
Figure 7.4
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22
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glucose
PP
ADPADP
Steps
+ 2
NAD+NAD+
PP
P
P P
ADPADP
P
H2O
P
NADH + H+
P P
P
P P
Energy-Investment Steps
- 2
H2O
ATP
ATP ATP
NADH + H+
Energy-Harvesting Steps
ATPATP ATP 1. Two ATP are used
to activate glucose.
2. A resulting C6 molecule breaksdown into 2 C3 molecules.
3. NAD+ takes an electronbecoming NADH + H+, withaddition of a second phosphateto the sugar.
4. Removal of high-energyphosphate from 2 BPG by 2 ADPproduces 2 ATP and 2 3PGmolecules.
5. Oxidation of 2 3PG by removalof water results in 2 high-energyPEP molecules.
BPG
3PG
PEP
BPG
3PG
PEP
G3P G3P
Figure 7.4
23
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PP
ADPADP
Steps
ATP+ 2
+ 2
(net gain)2
NAD+NAD+
PP
P
P P
ADPADP
P
ADP
H2O
ADP
P
NADH + H+
P P
P
P P
b.
Energy-Investment Steps
- 2
H2O
ATP
ATP
ATP
ATP
ATP
ATP
NADH + H+
Energy-Harvesting Steps
ATPATP ATP 1. Two ATP are used
to activate glucose.
2. A resulting C6 molecule breaks
down into 2 C3 molecules.
3. NAD+ takes an electron
becoming NADH + H+, with
addition of a second phosphateto the sugar.
4. Removal of high-energy
phosphate from 2 BPG by 2 ADP
produces 2 ATP and 2 3PGmolecules.
6. Removal of high-energy
phosphate from 2 PEP by 2
ADP produces 2 ATP and 2pyruvate molecules.
5. Oxidation of 2 3PG by removal
of water results in 2 high-energy
PEP molecules.
glucose
G3P G3P
BPGBPG
3PG3PG
PEPPEP
pyruvate pyruvate
Figure 7.4
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7.3 Outside the Mitochondria:
Fermentation
• If O2 is limited, cells may utilize anaerobic pathways, such as fermentation.
• In animal cells, pyruvate from glycolysis accepts two hydrogen ions and two electrons and is reduced to lactate.
• Yeast generates ethyl alcohol and CO2 by fermentation.
• Two NADH pass electrons to pyruvate to reduce it to lactate.
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Advantages and Disadvantages of Fermentation
• Fermentation is essential to humans since it can provide a rapid burst of ATP.
• In muscles working vigorously over a short period, fermentation is used to produce ATP as
O2 is in limited supply.
• Lactate is toxic to cells.
• As it accumulates, lactate changes the pH of the muscle cells, causing the “burn” feeling.
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Energy Yield of Fermentation
• Fermentation yields only two ATP by substrate-level ATP synthesis.
• These two ATP represent a small fraction of potential energy stored in glucose.
• In cellular respiration, 36 to 38 ATP molecules produced.
• Therefore, most of the potential energy stored in glucose has not been released.
27
inputs outputs
glucose
4 ADP + 2 P
ATP2
ATP2
ATP4
Fermentation
2 lactate or
2 alcohol and 2 CO2
2 ADP
net gain
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28Figure 7.5
+4 4
2
glucose
ATP–2
ATP
ATP
E1
2 ADP
2 NAD+
G3P
BPG
pyruvate
4 ADP
E2
2 P
P
2 alcohol2 lactate
2
E4
2
2
2
(net gain)
or
2 CO2
or
ATPE3
ATP
NADH2
Animalsand bacteria
Plantsand yeast
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29
Preparatory Reaction
• Preparatory Reaction
– Produces the molecule that will enter the citric
acid cycle.
• Reaction occurs in the cristae of mitochondria.
• Cristae are folds of the inner membrane that jut out into the matrix.
• 3C pyruvate is converted to 2C acetyl group.
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Preparatory Reaction
– Acetyl group attached to CoA to become acteyl CoA
– Carbon dioxide is produced.
– Hydrogen atoms are removed from pyruvate and picked up to form NADH + H+.
– This reaction occurs twice per glucose.Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2 acetyl—CoA + 2 carbon dioxide2 pyruvate + 2 CoA
2 NADH + H+2 NAD+
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Citric Acid Cycle
• Citric Acid Cycle
– Cyclical pathway that occurs in the matrix of
mitochondria
• A two-carbon acetyl group of Acetyl CoA combines with
a C4 molecule (oxaloacetate) to produce C6 citrate.
• The CoA is recycled to the preparatory reaction.
32
Citric Acid Cycle
– Each two-carbon acetyl group is oxidized to two CO2 molecules.
– Reactions produce three NADH + H+ and one
FADH2 .
– One ATP is produced by substrate-level ATP synthesis.
– Cycle turns twice per original glucose molecule.
33
inputs outputs
6 NAD+
2 ADP + 2 PATP2
Citric acid cycle
2 acetyl groups 4 CO2
6 NADH + H+
2 FADH22 FAD
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Citric Acid Cycle
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2 ADP 22
ATP
e–
NADH
e–
e–
Glycolysis
glucose pyruvatePreparatory reaction
2 ATP
2 ADP
4 ADP 4 ATP total
ATP net
Matrix
Citric acidcycle
NADH
NADHand FADH2
Electron transportchain and
chemiosmosis
32 ADPor 34
32or 34
ATP
e–
e–
e–
e–
Figure 7.6
35
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1. The C2 acetyl group combineswith a C4 molecule to produce
citrate, a C6 molecule.
C4
CoA
Citric acidcycle
Preparatoryreaction
CoA
acetyl CoA
Figure 7.6
36
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1. The C2 acetyl group combineswith a C4 molecule to producecitrate, a C6 molecule.
NAD+
CO2
NADH + H+
2. Oxidationreactionsproduce twoNADH + H+.
citrate
C4
CoA
C5
Citric acidcycle
Preparatoryreaction
CoA
acetyl CoA
Figure 7.6
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ATP
1. The C2 acetyl group combines
with a C4 molecule to producecitrate, a C6 molecule.
NAD+
NADH + H+
CO2
NADH + H+
CO2
2. Oxidation
reactionsproduce twoNADH + H+.
citrate
The loss of two
CO2 results In a new C4
molecule.
C4
One ATP is produced
by substrate-level
ATP synthesis.
CoA
4.
C4
NAD+C5
3.
Citric acid
cycle
Preparatory
reaction
CoA
acetyl CoA
Figure 7.6
38
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ATP
1. The C2 acetyl group combines
with a C4 molecule to producecitrate, a C6 molecule.
NADH + H+
NAD+
NADH + H+
CO2
NADH + H+
CO2
2. Oxidation
reactionsproduce twoNADH + H+.
citrate
The loss of two
CO2 results In a new C4
molecule.
C4
C4
One ATP is produced
by substrate-level
ATP synthesis.
NAD+
CoA
Additional oxidation reactions
produce an FADH2 and anotherNADH + H+ and regenerateoriginal C4 molecule.
4.
FAD
C4
FADH2
NAD+C5
5.
3.
Citric acid
cycle
Preparatory
reaction
CoA
acetyl CoA
Figure 7.6
39
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ATP
2 ADT 22
ATP
e–
NADH
e–
e–
Glycolysis
glucose pyruvatePreparatory reaction
2 ATP
2 ADP
4 ADP 4 ATP total
ATP net
1. The C2 acetyl group combines
with a C4 molecule to produce
citrate, a C6 molecule.
NADH + H+
Matrix
Citric acid
cycle
NADH
NADHand FADH2
Electron transportchain and
chemiosmosis
32 ADPor 34
32or 34
ATP
NAD+
NADH + H+
CO2
NADH + H+
CO2
2. Oxidation
reactions
produce two
NADH + H+.
citrate
The loss of two
CO2 results
In a new C4
molecule.
C4
C4
One ATP is producedby substrate-levelATP synthesis.
NAD+
CoA
Additional oxidation reactions
produce an FADH2 and another
NADH + H+ and regenerate
original C4 molecule.
4.
FAD
C4
FADH2
NAD+C5
e–
e–
e–
e–
5.
3.
Citric acid
cycle
Preparatory
reaction
CoA
acetyl CoA
Figure 7.6
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Electron Transport Chain
• Electron Transport Chain
– Located in cristae of mitochondria
• Electrons are passed to a series of electron carriers.
– Some carriers are cytochromes, iron-containing proteins.
• High-energy electrons enter system and low-energy
electrons leave the system.
• Two electrons per NADH + H+ and FADH2 enter the
electron transport chain.
• Each carrier reduced and then oxidized.
41
Electron Transport Chain
– As electrons pass from one carrier to another, energy is captured and stored as a hydrogen ion concentration gradient.
– Oxygen combines with hydrogen ions to form water.
– NAD+ and FAD are recycled to pick up more electrons from glycolysis, prep reaction, and citric acid cycle.
42
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2 ADT 22 ATP
NADH
e–
Glycolysis
glucose pyruvatePreparatory reaction
2 ATP
2 ADP
4 ADP 4 ATP total
ATP net
Citric acid
cycle
NADH
NADH and
FADH2
Electron transport
chain andchemiosmosis
32 or ADP
34
32 or
34
ATP
e–
e–
e–
e–
e–
e–
Figure 7.7
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43
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H2O
2H+
ADP + P
O212
ADP + P
ADP + P
ATP
ATP
ATP
FADH2
FAD + 2H+2e–
2e–
e–
e–
electron
carrier
2e–
2e–
2e–
made by
chemiosmosis
made by
chemiosmosis
made by
chemiosmosis
NAD+ + 2H+
NADH + H+
electron
carrier
electron
carrier
electron
carrier
electron
carrier
Figure 7.7
44
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H2O
2H+
ADP + P
O2
12
ADP + P
ADP + P
ATP
ATP
ATP
FADH2
FAD + 2H+2e–
2e–
e–
e–
electron
carrier
2e–
2e–
2e–
made by
chemiosmosis
made by
chemiosmosis
made by
chemiosmosis
NAD+ + 2H+
NADH + H+
electron
carrier
electron
carrier
electron
carrier
electron
carrier
2 ADT 22 ATP
NADH
e–
Glycolysis
glucose pyruv atePreparatory reaction
2 ATP
2 ADP
4 ADP 4 ATP total
ATP net
Citric acid
cycle
NADH
NADH and
FADH2
Electron transport
chain and
chemiosmosis
32 or ADP
34
32 or
34
ATP
e–
e–
e–
e–
e–
e–
Figure 7.7
45
Organization of Cristae
• Electron carriers are located in the cristae of the
mitochondria.
• NADH pass electrons to first acceptor of the
electron transport chain.
• As electrons pass along a series of electron
carriers, the energy released is used to pump H+
into the intermembrane space of mitochondrion.
• Protons accumulate in the intermembranous
space (proton gradient).
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Organization of Cristae
• The cristae also have ATP synthase
complexes.
• The H+ ions flow through an ATP synthase
complex, back into the matrix.
• As the H+ pass through the complex, energy is
released and captured to form ATP from ADP.
– This process is called chemiosmosis.
47
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cristae
intermembrane space matrix
Figure 7.8
48
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2
ADP + H2O
NAD+
H+
H+H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
P
2+
O212
Electron transportchain
proteincomplex
e-
FADH2
matrix
ATP synthase
complex
H+H+ATP
channelprotein
intermembrane
spacechemiosmosis
FAD
NADH + H+
ATP
e-
ATP
e-
e-e-
Figure 7.8
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49
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cristae
2
ADP + H2O
NAD+
H+
H+H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
P
2+
O212
intermembrane space matrix
Electron transportchain
protein
complex
e-
FADH2
matrix
ATP synthasecomplex
H+H+ATP
channelprotein
intermembranespace
chemiosmosis
FAD
NADH + H+
ATP
e-
ATP
e-
e-e-
Figure 7.8
50
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Energy Yield from Cellular Respiration
• What is the energy yield for the complete
breakdown of glucose to CO2 and H2O?
– Total of 4 ATP by substrate-level ATP synthesis
• 2 net from glycolysis
• 2 from citric acid cycle
– 32-34 ATP produced by electron transport chain and chemiosmosis
• Some cells have to pay to pump NADH from glycolysis into mitochondria
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Cyto
pla
sm
Mit
och
on
dri
on
Ele
ctr
on
tra
nsp
ort
ch
ain
2net
2
glucose
subtotal subtotal
2 CO2
4 CO2
FADH2
2
2
6
2
4 or 6
6
18
4
324
6 O2
ATP
or 34
ATP
ATP
ATP
ATPATP
ATP
ATP
ATP
2 pyruvate
2 acetyl CoA
Citric acidcycle
NADH + H+
NADH + H+
NADH + H+
glycolysis
6 H2O
36 or 38totalFigure 7.9
53
Efficiency of Cellular Respiration
• The difference in energy content of reactants (glucose and oxygen) and products (carbon dioxide and water) is 686 kcal.
• ATP phosphate bond has 7.3 kcal of energy.
• 36 ATP are produced in respiration.
• 36 X 7.3 = 263 kcal.
• 263/686 = 39% efficiency of energy capture.
• The rest of the energy is lost as heat.