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PowerLecture:
Chapter 8
How Cells Release Stored Energy
Impacts, Issues: When
Mitochondria Spin Their Wheels

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
When Mitochondria Spin Their Wheels
Fig. 8-1, p.122
“Killer” Bees
 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
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
Making ATP
 Plants
 Cells
make ATP during photosynthesis
of all organisms make ATP by
breaking down carbohydrates, fats, and
protein
Main Types of
Energy-Releasing Pathways
Anaerobic pathways
Aerobic pathways


Evolved first
 Don’t require oxygen
 Start with glycolysis in
cytoplasm
 Completed in
cytoplasm
Evolved later
 Require oxygen
 Start with glycolysis
in cytoplasm
 Completed in
mitochondria
Main Types of
Energy-Releasing Pathways
start (glycolysis) in
cytoplasm
start (glycolysis) in
cytoplasm
completed in
cytoplasm
completed in
mitochondrion
Anaerobic EnergyReleasing Pathways
Aerobic
Respiration
Fig. 8-2, p.124
Summary Equation for Aerobic
Respiration
C6H1206 + 6O2
glucose
oxygen
6CO2 + 6H20
carbon
water
dioxide
CYTOPLASM
2
glucose
ATP
4
Glycolysis
e- + H +
(2 ATP net)
2 pyruvate
2 NADH
e- + H +
2 CO2
Overview of Aerobic
Krebs
Respiration
Cycle
2 NADH
8 NADH
2 FADH2
e-
ATP
e- + H +
e-
+
4 CO2
H+
2
Electron
Transfer
Phosphorylation
H+
32
ATP
ATP
water
e- + oxygen
Typical Energy Yield: 36 ATP
Fig. 8-3, p. 135
The Role of Coenzymes
 NAD+
and FAD accept electrons and
hydrogen
 Become
 Deliver
NADH and FADH2
electrons and hydrogen to the
electron transfer chain
Glucose
 A simple
sugar
(C6H12O6)
 Atoms
held
together by
covalent bonds
In-text figure
Page 126
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
glucose
GYCOLYSIS
pyruvate
Glycolysis
to second stage of aerobic
respiration or to a different
energy-releasing pathway
GLUCOSE
Fig. 8-4a, p.126
Glycolysis
ATP
ENERGY-REQUIRING STEPS
OF GLYCOLYSIS
glucose
2 ATP invested
ADP
P
glucose–6–phosphate
P
fructose–6–phosphate
ATP
ADP
P
fructose–1,6–bisphosphate
P
DHAP
Fig. 8-4b, p.127
Glycolysis
P
P
PGAL
PGAL
NAD+
NAD+
NADH
Pi
P
P
ATP
NADH
Pi
P
1,3–bisphosphoglycerate
ADP
ENERGY-RELEASING STEPS
OF GLYCOLYSIS
P
1,3–bisphosphoglycerate
ADP
substrate-level
phsphorylation
ATP
2 ATP invested
P
3–phosphoglycerate
P
3–phosphoglycerate
Fig. 8-4c, p.127
Glycolysis
P
P
2–phosphoglycerate
2–phosphoglycerate
H2O
H2O
P
P
PEP
PEP
ADP
ATP
pyruvate
ADP
ATP
substrate-level
phsphorylation
2 ATP produced
pyruvate
Fig. 8-4d, p.127
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
Second Stage Reactions
 Preparatory


Pyruvate is oxidized into two-carbon acetyl
units and carbon dioxide
NAD+ is reduced
 Krebs


reactions
cycle
The acetyl units are oxidized to carbon
dioxide
NAD+ and FAD are reduced
Second Stage Reactions
inner
mitochondrial
membrane
outer
mitochondrial
membrane
inner
outer
compartment compartment
Fig. 8-6a, p.128
Preparatory Reactions
pyruvate
coenzyme A (CoA)
NAD+
NADH
O
CoA
acetyl-CoA
O carbon dioxide
The Krebs Cycle
Overall Reactants
Overall Products


Acetyl-CoA
 3 NAD+
 FAD
 ADP and Pi




Coenzyme A
2 CO2
3 NADH
FADH2
ATP
Acetyl-CoA
Formation
pyruvate
coenzyme A
(CO2)
Preparatory
Reactions
NAD+
NADH
CoA
acetyl-CoA
Krebs Cycle
CoA
oxaloacetate
citrate
NAD+
NADH
NADH
NAD+
FADH2
NAD+
FAD
NADH
ATP
ADP +
phosphate
group
Fig. 8-7a, p.129
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
Two pyruvates cross the inner
mitochondrial membrane.
Krebs
Cycle
2
NADH
6
NADH
2
FADH2
2
6 CO2
ATP
outer mitochondrial
compartment
inner mitochondrial
compartment
Eight NADH, two FADH 2,
and two ATP are the payoff
from the complete breakdown 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
Coenzyme Reductions during
First Two Stages
 Glycolysis
2 NADH
 Preparatory
reactions
 Krebs cycle
 Total
NADH
2 NADH
2 FADH2 + 6 NADH
2 FADH2 + 10
Phosphorylation
glucose
ATP
2 PGAL
ATP
2 NADH
2 pyruvate
glycolysis
2 CO2
2 FADH2
e–
2 acetyl-CoA
2 NADH
H+
H+
2
ATP
6 NADH
Krebs
Cycle
KREBS
CYCLE
ATP
2 FADH2
4 CO2
H+
H+
ATP
36 ATP
electron
transfer
phosphorylation
H+
H+
ADP
+ Pi
H+
H+
H+
Fig. 8-9, p.131
Electron Transfer
Phosphorylation
 Occurs
in the mitochondria
 Coenzymes deliver electrons to electron
transfer chains
Creating an H+ Gradient
Electron transfer sets up H+ ion gradients
OUTER COMPARTMENT
NADH
INNER COMPARTMENT
Making ATP:
Chemiosmotic Model
Flow of H+ down gradients powers ATP formation
ATP
INNER
COMPARTMENT
ADP
+
Pi
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
Anaerobic Pathways
 Do
not use oxygen
 Produce
 Two
less ATP than aerobic pathways
types

Fermentation pathways

Anaerobic electron transport
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+
glycolysis
C6H12O6
2
ATP
energy input
2 ADP
2 NAD+
2
4
Alcoholic
Fermentation
NADH
ATP
energy output
2 pyruvate
2 ATP net
ethanol
formation
2 H2O
2 CO2
2 acetaldehyde
electrons, hydrogen
from NADH
2 ethanol
Fig. 8-10d, p.132
glycolysis
2
C6H12O6
Lactate
Fermentation
ATP
energy input
2 NAD+
2 ADP
2
4
NADH
ATP
energy output
2 pyruvate
2 ATP net
lactate
fermentation
electrons, hydrogen
from NADH
2 lactate
Fig. 8-11, p.133
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
Summary of Energy Harvest
(per molecule of glucose)

Glycolysis


Krebs cycle and preparatory reactions


2 ATP formed by substrate-level phosphorylation
2 ATP formed by substrate-level phosphorylation
Electron transport phosphorylation

32 ATP formed
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+
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
FOOD
fats
fatty
acids
glycogen
glycerol
complex
carbohydrates
proteins
simple sugars
(e.g., glucose)
amino acids
NH3
glucose-6phosphate
urea
carbon
backbones
Alternative
Energy
Sources
PGAL
2
glycolysis
ATP
4 ATP
(2 ATP net)
NADH
pyruvate
acetyl-CoA
NADH
NADH,
FADH2
CO2
Krebs
Cycle
2 ATP
CO2
e–
ATP
electron transfer
phosphorylation
H+
ATP
ATP
many ATP
water
e– + oxygen
Fig. 8-13b, p.135
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
Processes Are Linked
p.136b