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Chapter 7: Respiration
Respiration: The release of stored energy
(sugar). Usually involves oxygen (the reason we
breath is to release energy from our food).
Aerobic vs Anaerobic: Aerobic means in the
presence of oxygen.
Mitochondrion
Inner Membrane
Inner Space
Outer Membrane
First Stage: Glycolysis
BASICS:
Glycolysis doesn’t require oxygen (anaerobic)!
Glycolysis doesn’t occur in the mitochondria, so it
can happen in prokaryotes (lacking organelles).
Glycolysis occurs in the cytoplasm.
Glycolysis begins with glucose and ends with two
pyruvate molecules, yielding minimal energy
gain.
First Stage: Glycolysis
1. Two ATP are invested to rearrange
glucose.
2. When glucose is split into two 3-carbon
compounds, energy is released.
3. Released energy is stored in 4 ATP
(through substrate-level phosphorylation,
or direct transfer of phosphate group).
4. NAD+ picks up e- and H+ to become
NADH
ENERGY-REQUIRING STEPS
OF GLYCOLYSIS
glucose
ATP
ADP
2 ATP invested
P
glucose-6-phosphate
P
fructose-6-phosphate
ATP
ADP
P
fructose-1,6-bisphosphate
(see next slide)
Fig. 8.4b, p. 135
ENERGY-RELEASING STEPS
OF GLYCOLYSIS
PGAL
PGAL
NAD+
NADH
Pi
P
P
NAD+
NADH
Pi
P
1,3-bisphosphoglycerate
P
1,3-bisphosphoglycerate
ATP
ATP
substrate-level
phosphorylation
2 ATP invested
P
P
3-phosphoglycerate
3-phosphoglycerate
P
P
2-phosphoglycerate
H2
O
2-phosphoglycerate
H2
O
PEP
PEP
P
ADP
ATP
P
ADP
ATP
substrate-level
phosphorylation
2 ATP invested
pyruvate
pyruvate
to second set of reactions
Fig. 8.4c, p. 135
Second Step: Krebs Cycle
1. Two pyruvate molecules enter the
mitochondrion (enter into the inner
compartment of mito).
2. Coenzyme-A strips a carbon, yielding
CO2.
3. Acetyl-CoA enters Krebs Cycle/Citric
Acid Cycle, yielding more CO2.
4. Final yield: ATP, NADH, FADH2.
1 Pyruvate from
cytoplasm inters
inner mitochondrial
compartment.
OUTER COMPARTMENT
NADH
acetyl-CoA
Krebs
Cycle
NADH
NADH
3 NADH and
FADH2 give up
electrons and
H+ to membranebound electron
transport systems.
ATP
2 Krebs cycle and
preparatory steps:
NAD+ and FADH2
accept electrons and
hydrogen stripped
ADP
from the pyruvate.
+ Pi
ATP forms. Carbon
dioxide forms.
INNER COMPARTMENT
4 As electrons
move through the
transport system,
H+ is pumped to
outer compartment.
ATP
ATP
ATP
5 Oxygen
accepts
electrons,
joins with H+
to form water.
free oxygen
6 Following its gradients, H+ flows back
into inner compartment, through ATP
synthases. The flow drives ATP formation.
Fig. 8.5b, p. 136
PREPARATORY
STEPS
pyruvate
coenzyme A (CoA)
NAD+
(CO2)
NADH
CoA
Acetyl–CoA
KREBS CYCLE
CoA
oxaloacetate
citrate H O
2
NADH
H2O
NAD+
malate
NAD+
H2O
isocitrate
NADH
fumarate
FADH2
FAD
a-ketogluterate
CoA
NAD+
NADH
succinate
CoA
succinyl–CoA
ATP
ADP + phosphate
group (from GTP)
Fig. 8.6, p. 137
Step 3: Electron Transfer
Phosphorylation
1. NADH and FADH2 transfer e- and H+ to
inner membrane of mitochondria, buiding
up concentration of protons in
intermembrane space.
2. When protons flow through ATP
synthases, up to 34 ATP are produced.
3. Oxygen will accept extra hydrogens,
resulting in water.
Electron Transport Chain
ATP Synthase
1 Pyruvate from
cytoplasm inters
inner mitochondrial
compartment.
OUTER COMPARTMENT
NADH
acetyl-CoA
Krebs
Cycle
NADH
NADH
3 NADH and
FADH2 give up
electrons and
H+ to membranebound electron
transport systems.
ATP
2 Krebs cycle and
preparatory steps:
NAD+ and FADH2
accept electrons and
hydrogen stripped
ADP
from the pyruvate.
+ Pi
ATP forms. Carbon
dioxide forms.
INNER COMPARTMENT
4 As electrons
move through the
transport system,
H+ is pumped to
outer compartment.
ATP
ATP
ATP
5 Oxygen
accepts
electrons,
joins with H+
to form water.
free oxygen
6 Following its gradients, H+ flows back
into inner compartment, through ATP
synthases. The flow drives ATP formation.
Fig. 8.5b, p. 136
Possible Pathways
Glucose
(no oxygen,
for muscle)
Lactate
Fermentation
Glycolysis
(if oxygen)
(no oxygen for
yeast, bacteria)
Alcoholic
Fermentation
Aerobic Respiration (in mitochondria)
Alcoholic Fermentation (anaerobic)
If no oxygen is available, only
glycolysis can occur.
In this case, pyruvate doesn’t enter
the mitochondrion but rather is
modified in the cytoplasm.
The result is ethanol and carbon
dioxide.
Very little energy release as
compared to aerobic respiration, so
not an option for large, active animals.
Lactic Acid Fermentation (anaerobic)
If no oxygen is available, only
glycolysis can occur.
In this case, pyruvate doesn’t
enter the mitochondrion but
rather is modified in the
cytoplasm.
The result is lactate.
Very little energy release as
compared to aerobic respiration,
so only used for short bursts of
energy.