how cells release stored energy. more than 100 mitochondrial disorders are known friedreich’s...
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CELLULAR RESPIRATIONChapter 8
How Cells Release Stored Energy
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More than 100 mitochondrial disorders are known
Friedreich’s ataxia, caused by a mutant gene, results in loss of cordination, weak muscles, and visual problems
Animal, plants, fungus, and most protists depend on structurally sound mitochondria
Defective mitochondria can result in life threatening disorders
Impacts, Issues: When Mitochondria Spin Their Wheels
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p.123
When Mitochondria Spin Their Wheels
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Descendents of African honeybees that
were imported to Brazil in the 1950s
More aggressive, wider-ranging than other
honeybees
Africanized bee’s muscle cells have large
mitochondria
“Killer” Bees
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Photosynthesizers get energy from the sun
Animals get energy second- or third-hand from plants or other organisms
Regardless, the energy is converted to the chemical bond energy of ATP
ATP Is Universal Energy Source
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Anaerobic pathways
Evolved first Don’t require oxygen Start with glycolysis
in cytoplasm Completed in
cytoplasm
Aerobic pathways
Evolved later Require oxygen Start with
glycolysis in cytoplasm
Completed in mitochondria
Main Types of Energy-Releasing Pathways
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start (glycolysis) in cytoplasm
completed in mitochondrion
start (glycolysis) in cytoplasm
completed in cytoplasm
Aerobic Respiration
Anaerobic Energy-Releasing Pathways
Fig. 8-2, p.124
Main Types of Energy-Releasing Pathways
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C6H1206 + 6O2 6CO2 + 6H20
glucose oxygen carbon water
dioxide
Summary Equation for Aerobic Respiration
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Overview of Aerobic Respiration
CYTOPLASM
Glycolysis
Electron Transfer
Phosphorylation
Krebs CYCL
E
ATP
ATP
2 CO2
4 CO2
2
32
water
2 NADH
8 NADH
2 FADH2
2 NADH 2 pyruvate
e- + H+
e- + oxygen
(2 ATP net)
glucose
Typical Energy Yield: 36 ATP
e-
e- + H+
e- + H+
ATP
H+
e- + H+
ATP2 4
Fig. 8-3, p. 135
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NAD+ and FAD accept electrons and
hydrogen
Become NADH and FADH2
Deliver electrons and hydrogen to the
electron transfer chain
The Role of Coenzymes
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A simple sugar(C6H12O6)
Atoms held together by covalent bonds
Glucose
In-text figurePage 126
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Energy-requiring steps◦ ATP energy activates glucose and its six-
carbon derivatives
Energy-releasing steps◦ The products of the first part are split into
three-carbon pyruvate molecules
◦ ATP and NADH form
Glycolysis Occurs in Two Stages
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GLUCOSE
glucose
GYCOLYSIS
pyruvate
to second stage of aerobicrespiration or to a differentenergy-releasing pathway
Fig. 8-4a, p.126
Glycolysis
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ATP
ATP
2 ATP invested
ENERGY-REQUIRING STEPSOF GLYCOLYSIS
glucose
ADP
ADP
P
P
P
P
glucose–6–phosphate
fructose–6–phosphate
fructose–1,6–bisphosphate DHAP
Fig. 8-4b, p.127
Glycolysis
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ATPADP
ENERGY-RELEASING STEPSOF GLYCOLYSIS
NAD+
P
PGAL
1,3–bisphosphoglyceratesubstrate-levelphsphorylation
Pi
1,3–bisphosphoglycerate
ATP
NADHNADH
P
PGALNAD+
Pi
P PP P
3–phosphoglycerate 3–phosphoglycerateP P
2 ATP invested
ADP
Fig. 8-4c, p.127
Glycolysis
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2 ATP produced
ATPADP
P
substrate-levelphsphorylation
2–phosphoglycerate
ATP
P
pyruvate pyruvate
ADP
P P
2–phosphoglycerate
H2O H2O
PEP PEP
Fig. 8-4d, p.127
Glycolysis
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Energy-Requiring Steps
2 ATP investedEnergy-Requiring Steps of Glycolysis
glucose
PGAL PGALPP
ADP
P
ATP
glucose-6-phosphate
Pfructose-6-phosphate
ATP
fructose1,6-bisphosphate
P P
ADP
Figure 8-4(2)
Page 127
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Energy-Releasing Steps
ADPATP
pyruvate
ADPATP
pyruvate
H2
OP
PEP
H2
OP
PEP
P
2-phosphoglycerate
P
2-phosphoglycerate
ADPATP
P3-phosphoglycerate
ADPATP
P3-phosphoglycerate
NAD+
NADHPi
1,3-bisphosphoglycerateP P
NAD+
NADHPi
1,3-bisphosphoglycerateP P
PGAL
PPGAL
P
Figure 8-4 Page 127
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Energy requiring steps: 2 ATP invested
Energy releasing steps:2 NADH formed 4 ATP formed
Net yield is 2 ATP and 2 NADH
Glycolysis: Net Energy Yield
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Preparatory reactions◦ Pyruvate is oxidized into two-carbon acetyl units
and carbon dioxide◦ NAD+ is reduced
Krebs cycle◦ The acetyl units are oxidized to carbon dioxide◦ NAD+ and FAD are reduced
Second Stage Reactions
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Fig. 8-5a, p.128
mitochondrion
mitochondrion
Second Stage Reactions
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innermitochondrial
membrane
outermitochondrial
membrane
innercompartment
outercompartment
Fig. 8-6a, p.128
Second Stage Reactions
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Two pyruvates cross the innermitochondrial membrane.
outer mitochondrialcompartment
NADH
NADH
FADH2
ATP
2
6
2
2
KrebsCycle
6 CO2
inner mitochondrialcompartment
Eight NADH, two FADH 2, and two ATP are the payoff from the complete break-down of two pyruvates in the second-stage reactions.
The six carbon atoms from two pyruvates diffuse out of the mitochondrion, then out of the cell, in six CO
Fig. 8-6b, p.128
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Preparatory Reactions
pyruvate
NAD+
NADH
coenzyme A (CoA)
O Ocarbon dioxide
CoAacetyl-CoA
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Acetyl-CoAFormation
acetyl-CoA
(CO2)
pyruvatecoenzyme A NAD+
NADH
CoA
Krebs Cycle CoA
NADH
FADH2
NADH
NADH
ATP ADP + phosphategroup
NAD+
NAD+
NAD+
FAD
oxaloacetate citrate
Fig. 8-7a, p.129
Preparatory Reactions
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glucose
GLYCOLYSIS
pyruvate
KREBSCYCLE
ELECTRON TRANSFERPHOSPHORYLATION
Fig. 8-7b, p.129
Preparatory Reactions
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Overall Reactants
Acetyl-CoA 3 NAD+
FAD ADP and Pi
Overall Products
Coenzyme A 2 CO2
3 NADH FADH2
ATP
The Krebs Cycle
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Krebs Cycle
NAD+
NADH
=CoAacetyl-CoA
oxaloacetate citrate
CoA
H2
O
malate isocitrate
H2
OH2
O
FAD
FADH2
fumarate
succinate
ADP + phosphate
groupATP
succinyl-CoA
O O
CoANAD+
NADH
O ONAD+
NADH
a-ketoglutarate
Figure 8-6Page 129
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All of the carbon molecules in pyruvate end up in carbon dioxide
Coenzymes are reduced (they pick up electrons and hydrogen)
One molecule of ATP forms Four-carbon oxaloacetate regenerates
Results of the Second Stage
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Glycolysis 2 NADH Preparatory
reactions 2 NADH Krebs cycle 2 FADH2 + 6 NADH
Total 2 FADH2 + 10 NADH
Coenzyme Reductions during First Two Stages
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Occurs in the mitochondria Coenzymes deliver electrons to electron
transfer chains Electron transfer sets up H+ ion gradients Flow of H+ down gradients powers ATP
formation
Electron Transfer Phosphorylation
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glucose
GLYCOLYSIS
pyruvate
KREBSCYCLE
ELECTRON TRANSFERPHOSPHORYLATION
Fig. 8-8a, p.130
Phosphorylation
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Fig. 8-8b, p.130
OUTER COMPARTMENT
INNER COMPARTMENT
Electron Transfer Chain ATP Synthase
ATP
H+
H+H+
H+
H+
H+
H+H+
H+H+
H+
H+H+
H+
H+
H+
H+
H+H+
H+
H+
H+
H+
H+
NADH + H+NAD+ + 2H+ FAD + 2H+FADH2 2H+ + 1/2 02 H2O ADP + Pi
e-e- e-
Phosphorylation
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glucose
glycolysis
e–
KREBSCYCLE
electrontransfer
phosphorylation
2 PGAL
2 pyruvate
2 NADH
2 CO2
ATP
ATP
2 FADH2
H+
2 NADH
6 NADH
2 FADH2
2 acetyl-CoA
ATP2 KrebsCycle
4 CO2
ATP
ATP
ATP
36
ADP + Pi
H+
H+
H+
H+
H+
H+
H+
H+
Fig. 8-9, p.131
Phosphorylation
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Creating an H+ Gradient
NADH
OUTER COMPARTMENT
INNER COMPARTMENT
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Making ATP: Chemiosmotic Model
ATP
ADP+Pi
INNER COMPARTMENT
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Electron transport phosphorylation requires the presence of oxygen
Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water
Importance of Oxygen
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Glycolysis◦ 2 ATP formed by substrate-level
phosphorylation Krebs cycle and preparatory reactions
◦ 2 ATP formed by substrate-level phosphorylation
Electron transport phosphorylation◦ 32 ATP formed
Summary of Energy Harvest(per molecule of glucose)
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NADH formed in cytoplasm cannot enter mitochondrion
It delivers electrons to mitochondrial membrane
Membrane proteins shuttle electrons to NAD+ or FAD inside mitochondrion
Electrons given to FAD yield less ATP than those given to NAD+
Energy Harvest Varies
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686 kcal of energy are released
7.5 kcal are conserved in each ATP
When 36 ATP form, 270 kcal (36 X 7.5) are
captured in ATP
Efficiency is 270 / 686 X 100 = 39 percent
Most energy is lost as heat
Efficiency of Aerobic Respiration
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Do not use oxygen
Produce less ATP than aerobic pathways
Two types
◦ Fermentation pathways
◦ Anaerobic electron transport
Anaerobic Pathways
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Begin with glycolysis
Do not break glucose down completely to
carbon dioxide and water
Yield only the 2 ATP from glycolysis
Steps that follow glycolysis serve only to
regenerate NAD+
Fermentation Pathways
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C6H12O6
ATP
ATPNADH
2 acetaldehyde
electrons, hydrogen from NADH
2 NAD+
2
2 ADP
2 pyruvate
2
4
energy output
energy input
glycolysis
ethanol formation
2 ATP net
2 ethanol
2 H2O
2 CO2
Fig. 8-10d, p.132
Alcoholic Fermentati
on
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C6H12O6
ATP
ATPNADH
2 lactate
electrons, hydrogen from NADH
2 NAD+
2
2 ADP
2 pyruvate
2
4
energy output
energy input
glycolysis
lactate fermentatio
n
2 ATP net
Fig. 8-11, p.133
Lactate Fermentation
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Fig. 8-12, p.133
Lactate Fermentation
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Carried out by certain bacteria Electron transfer chain is in bacterial
plasma membrane Final electron acceptor is compound from
environment (such as nitrate), not oxygen ATP yield is low
Anaerobic Electron Transport
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FOOD
complex carbohydrates
simple sugars
pyruvate
acetyl-CoA
glycogenfats proteins
amino acids
carbon backbones
fatty acids
glycerol
NH3
PGAL
glucose-6-phosphate
GLYCOLYSIS
KREBS CYCLE
urea
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FOOD
fats glycogencomplex
carbohydrates
proteins
simple sugars(e.g., glucose) amino acids
glucose-6-phosphate
carbon backbone
s
NH3
urea
ATP
(2 ATP net)
PGAL
glycolysisATP2
glycerolfatty acids
NADH pyruvate
acetyl-CoA
NADH CO2
KrebsCycle
NADH,FADH2
CO2
ATP
ATPATP
many ATP
waterH+
e– + oxygen
e–
4
ATP2
Fig. 8-13b, p.135
electron transfer phosphorylation
Alternative Energy Sources
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When life originated, atmosphere had little
oxygen
Earliest organisms used anaerobic
pathways
Later, noncyclic pathway of
photosynthesis increased atmospheric
oxygen
Cells arose that used oxygen as final
acceptor in electron transport
Evolution of Metabolic Pathways
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p.136b
Processes Are Linked