You Light Up My Life

1
PowerLectureChapter 8
How Cells Release Stored Energy
2
Impacts, Issues When Mitochondria Spin Their
Wheels

• More than 100 mitochondrial disorders are known
• Friedreichs 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

3
When Mitochondria Spin Their Wheels
Fig. 8-1, p.122
4
Killer Bees

• Descendents of African honeybees that were
  imported to Brazil in the 1950s
• More aggressive, wider-ranging than other
  honeybees
• Africanized bees muscle cells have large
  mitochondria

5
ATP Is Universal Energy Source

• 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

6
Making ATP

• Plants make ATP during photosynthesis
• Cells of all organisms make ATP by breaking down
  carbohydrates, fats, and protein

7
Main Types of Energy-Releasing Pathways

• Aerobic pathways
• Evolved later
• Require oxygen
• Start with glycolysis in cytoplasm
• Completed in mitochondria

• Anaerobic pathways
• Evolved first
• Dont require oxygen
• Start with glycolysis in cytoplasm
• Completed in cytoplasm

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Main Types of Energy-Releasing Pathways
start (glycolysis) in cytoplasm
start (glycolysis) in cytoplasm
completed in cytoplasm
completed in mitochondrion
Aerobic Respiration
Anaerobic Energy-Releasing Pathways
Fig. 8-2, p.124
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Summary Equation for Aerobic Respiration
C6H1206 6O2 6CO2 6H20
glucose oxygen carbon
water dioxide
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CYTOPLASM
glucose
ATP
4
2
ATP
Glycolysis
(2 ATP net)
e- H
2 pyruvate
2 NADH
Overview of Aerobic Respiration
e- H
2 CO2
2 NADH
e- H
4 CO2
8 NADH
KrebsCycle
e- H
2
ATP
2 FADH2
e-
Electron Transfer Phosphorylation
32
ATP
water
H
e- oxygen
Typical Energy Yield 36 ATP
Fig. 8-3, p. 135
11
The Role of Coenzymes

• NAD and FAD accept electrons and hydrogen
• Become NADH and FADH2
• Deliver electrons and hydrogen to the electron
  transfer chain

12
Glucose

• A simple sugar
• (C6H12O6)
• Atoms held together by covalent bonds

In-text figurePage 126
13
Glycolysis Occurs in Two Stages

• 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

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glucose
Glycolysis
GYCOLYSIS
pyruvate
to second stage of aerobic respiration or to a
different energy-releasing pathway
GLUCOSE
Fig. 8-4a, p.126
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Glycolysis
ENERGY-REQUIRING STEPS OF GLYCOLYSIS
glucose
ATP
2 ATP invested
ADP
P
glucose6phosphate
P
fructose6phosphate
ATP
ADP
P
P
fructose1,6bisphosphate
DHAP
Fig. 8-4b, p.127
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Glycolysis
ENERGY-RELEASING STEPS OF GLYCOLYSIS
P
P
PGAL
PGAL
NAD
NAD
NADH
NADH
Pi
Pi
P
P
P
P
1,3bisphosphoglycerate
1,3bisphosphoglycerate
substrate-level phsphorylation
ADP
ADP
ATP
ATP
2 ATP invested
P
P
3phosphoglycerate
3phosphoglycerate
Fig. 8-4c, p.127
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Glycolysis
P
P
2phosphoglycerate
2phosphoglycerate
H2O
H2O
P
P
PEP
PEP
substrate-level phsphorylation
ADP
ADP
ATP
ATP
2 ATP produced
pyruvate
pyruvate
Fig. 8-4d, p.127
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Glycolysis Net Energy Yield
Energy requiring steps 2 ATP invested
Energy releasing steps 2 NADH formed 4
ATP formed Net yield is 2 ATP and 2 NADH
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Second Stage Reactions

• 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

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Second Stage Reactions
inner mitochondrial membrane
outer mitochondrial membrane
inner compartment
outer compartment
Fig. 8-6a, p.128
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Preparatory Reactions
pyruvate
coenzyme A (CoA)
NAD
carbon dioxide
NADH
CoA
acetyl-CoA
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The Krebs Cycle

• Overall Products
• Coenzyme A
• 2 CO2
• 3 NADH
• FADH2
• ATP

• Overall Reactants
• Acetyl-CoA
• 3 NAD
• FAD
• ADP and Pi

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Acetyl-CoA Formation
pyruvate
Preparatory Reactions
coenzyme A
NAD
(CO2)
NADH
CoA
acetyl-CoA
Krebs Cycle
CoA
oxaloacetate
citrate
NAD
NADH
NADH
NAD
FADH2
NAD
FAD
NADH
ADP phosphate group
ATP
Fig. 8-7a, p.129
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Results of the Second Stage

• 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

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Two pyruvates cross the inner mitochondrial
membrane.
outer mitochondrial compartment
inner mitochondrial compartment
NADH
2
NADH
6
Krebs Cycle
Eight NADH, two FADH 2, and two ATP are the
payoff from the complete break-down of two
pyruvates in the second-stage reactions.
FADH2
2
ATP
2
The six carbon atoms from two pyruvates diffuse
out of the mitochondrion, then out of the cell,
in six CO
6 CO2
Fig. 8-6b, p.128
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Coenzyme Reductions during First Two Stages

• Glycolysis 2 NADH
• Preparatory
• reactions 2 NADH
• Krebs cycle 2 FADH2 6 NADH
• Total 2 FADH2 10 NADH

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Phosphorylation
glucose
ATP
2 PGAL
ATP
2 NADH
2 pyruvate
glycolysis
2 FADH2
2 CO2
e
2 acetyl-CoA
2 NADH
H
H
KREBS CYCLE
6 NADH
2
ATP
Krebs Cycle
ATP
H
2 FADH2
ATP
H
4 CO2
36
ATP
H
H
ADP Pi
electron transfer phosphorylation
H
H
H
Fig. 8-9, p.131
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Electron Transfer Phosphorylation

• Occurs in the mitochondria
• Coenzymes deliver electrons to electron transfer
  chains

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Creating an H Gradient
Electron transfer sets up H ion gradients
OUTER COMPARTMENT
NADH
INNER COMPARTMENT
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Making ATP Chemiosmotic Model
Flow of H down gradients powers ATP formation
ATP
INNER COMPARTMENT
ADPPi
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Importance of Oxygen

• Electron transport phosphorylation requires the
  presence of oxygen
• Oxygen withdraws spent electrons from the
  electron transfer chain, then combines with H to
  form water

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Anaerobic Pathways

• Do not use oxygen
• Produce less ATP than aerobic pathways
• Two types
• Fermentation pathways
• Anaerobic electron transport

36
Fermentation Pathways

• 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

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glycolysis
Alcoholic Fermentation
C6H12O6
ATP
2
2 ADP
energy input
2 NAD
NADH
2
ATP
4
2 pyruvate
energy output
2 ATP net
ethanol formation
2 H2O
2 CO2
2 acetaldehyde
electrons, hydrogen from NADH
2 ethanol
Fig. 8-10d, p.132
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Lactate Fermentation
glycolysis
C6H12O6
ATP
2
energy input
2 ADP
2 NAD
NADH
2
4
ATP
2 pyruvate
energy output
2 ATP net
lactate fermentation
electrons, hydrogen from NADH
2 lactate
Fig. 8-11, p.133
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Anaerobic Electron Transport

• 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

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Summary of Energy Harvest(per molecule of
glucose)

• 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

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Energy Harvest Varies

• 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

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Efficiency of Aerobic Respiration

• 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

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Alternative Energy Sources
FOOD
complex carbohydrates
fats
glycogen
proteins
simple sugars (e.g., glucose)
fatty acids
amino acids
glycerol
NH3
carbon backbones
glucose-6-phosphate
urea
PGAL
glycolysis
4
ATP
2
ATP
(2 ATP net)
NADH
pyruvate
acetyl-CoA
NADH
CO2
Krebs Cycle
NADH, FADH2
2
ATP
CO2
e
ATP
ATP
electron transfer phosphorylation
ATP
many ATP
water
H
e oxygen
Fig. 8-13b, p.135
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Evolution of Metabolic Pathways

• 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

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Processes Are Linked
p.136b