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Cellular Respiration
Chemical Equation
6 O2 + C6H12O6  6 H2O + 6 CO2 + ATP
Page 107
Adenosine Triphosphate
Adenosine Diphosphate
Background
Aerobic= requires oxygen
Anaerobic= does not require oxygen
Usually think of respiration as breathing,
but cellular respiration refers to the
energy-releasing pathways
However, we breathe to get oxygen to fuel the
cellular respiration
1st Step- Glycolysis (breaking apart
glucose)
Occurs in the cytoplasm
Requires 2 ATP to make 4 ATP = NET
GAIN OF 2 ATP
Pyruvate is made
Next step depends on whether there is
oxygen present or not…
Step 2-If oxygen is present…aerobic
Glycolysis is followed by the Krebs
cycle/Citric Acid Cycle and then the
electron transport chain
Occurs in the mitochondria
Yields 34 more ATP
2a- Krebs Cycle
Pyruvate is broken down into carbon
dioxide in a series of energy-extracting
reactions. (thus resulting in the CO2 we
exhale)
2 ATPs are made
High energy electrons transferred to
electron carriers, (NAD+, FADH) NADH &
FADH2
The Citric Acid Cycle
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NADH
NADH
NADH and
FADH2
Glycolysis
glucose
pyruvate
Preparatory reaction
Citric acid
cycle
Electron transport
chain and
chemiosmosis
2 ATP
2 ADP
4 ADP
4 ATP total
2 ATP
net
2 ADP
2
ATP
32 ADP
32
or 34
NADH
ATP
NAD+
or 34
1. The cycle begins when
an acetyl group carried by
CoA combines with a C4
molecule to form citrate.
citrate
C6
CO2
CoA
2. Twice over, substrates
are oxidized as NAD+ is
reduced to NADH,
and CO2 is released.
ketoglutarate
C5
acetyl CoA
Citric acid
cycle
NAD+
oxaloacetate
C4
NADH
NADH
5. Once again a substrate
is oxidized, and NAD+
is reduced to NADH.
succinate
C4
NAD+
CO2
fumarate
C4
FAD
4. Again a substrate is
oxidized, but this time
FAD is reduced to FADH2.
FADH2
ATP
3. ATP is produced as an
energized phosphate is
transferred from a substrate
to ADP.
Citric Acid Cycle: Balance Sheet
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Citric acid cycle
inputs
outputs
2 pyruvates
6 NAD+
2 FAD
4 CO2
6 NADH
2 ADP + 2 P
2 FADH2
2
ATP
9
Electron Transport Chain
ETC uses high energy electrons from the
Krebs cycle to convert ADP to ATP.
Massive amounts of ATP are generated.
(32 ATPs)
Oxygen is a reactant & water is also a
product
Electron Transport Chain
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e–
NADH
NADH
e–
e–
e–
Glycolysis
glucose
pyruvate
e–
NADH and
FADH2
e–
e–
Citric acid
cycle
Preparatory reaction
Electron transport
chain and
chemiosmosis
2 ATP
2 ATP
4 ADP
4 ADP total
2
ADP
net
2 ADP
2
ADP
32 or ADP 32 or ADP
34
34
NADH +H+
eNAD+ + 2H+
NADH-Q
reductase
P
2e-
ATP
made by
chemiosmosis
e-
coenzyme Q
FADH2
2e-
FAD + 2H+
cytochrome
reductase
ADP + P
2e-
ATP
made by
chemiosmosis
ATP
made by
chemiosmosis
cytochrome
c
2e-
cytochrome
oxidase
ADP + P
2e2
1/
11
2 O2
H+
H2O
Overall Energy Yielded per Glucose
Molecule
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glycolysis
2
net
ATP
2
NADH
2
NADH
6
NADH
2
FADH
2 pyruvate
Mitochondrion
2 acetyl CoA
2 CO2
2
ATP
Citric acid
cycle
4 CO2
6
ATP
18
ATP
4
ATPP
6 H2O
subtotal
32
or 34
ATP
36 or 38
total
12
ATP
2
6
O2
subtotal
4
4 or 6
Electron transport chain
Cytoplasm
glucose
ATP
ATP
Energy and Exercise
 Quick energy- cells contain enough ATP for a
few seconds
Lactic acid fermentation- can provide enough energy for
about 90 seconds of work
 Reason a runner breathes so heavily after a race
 Lactic acid causes “soreness”
 Long-Term energy- comes from respiration
comes from glycogen stored in cells for 15 – 20 minutes
After that, body breaks down other stored food
molecules, including fats
 Reason aerobic exercise is beneficial for weight control
The Metabolic Pool Concept
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proteins
carbohydrates
amino
acids
glucose
Glycolysis
fats
glycerol
ATP
pyruvate
acetyl CoA
Citric
acid
cycle
ATP
Electron
transport
chain
ATP
© C Squared Studios/Getty Images.
14
fatty
acids
Vocabulary
 Calorie- the amount of energy needed to raise
the temperature of 1 gram of water 1 degree
Celsius
 Glycolysis- the process in which one molecule of
glucose is broken in half , producing two
molecules of pyruvic acid.
 Cellular respiration- the process that releases
energy by breaking down glucose and other
food molecules in the presence of oxygen
 NAD+ - an electron carrier
 Fermentation- the pathway that allows glycolysis
to continue by returning electrons to pyruvic acid
Anaerobic- oxygen is not required
Aerobic- oxygen is required
Kreb’s cycle- the process in which pyruvic
acid is broken down into carbon dioxide in
a series of energy-releasing steps
Electron transport chain- the process in
which high-energy electrons convert ADP
to ATP (a lot of it).
ATP- the principal chemical compound
that cells use to store and release energy
Step 2-If oxygen is not present =
anaerobic
Fermentation- process that allows
glycolysis to continue by returning
electrons to pyruvate
Therefore, 2 more ATP’s will be made…then 2
more…then 2 more
Two Types of Fermentation
Alcoholic fermentation- occurs in yeast and bacteria
 Yeast are unicellular eukaryotic fungi that carry out
aerobic respiration, however when oxygen is not
available, they can switch to anaerobic respiration
• Pyruvate + NADH  ethanol + NAD+ + CO2
• Very important in industry…alcohol, bread, ethanol for fuel
Lactic acid fermentation – occurs in muscles
 During strenuous exercise when your lungs cannot
provide you with enough oxygen, your muscles switch to
lactic acid fermentation…most of the lactic acid diffuses
into the bloodstream and goes to the liver to be converted
back to Pyruvate, however some remains and causes
“soreness”.
• Pyruvate + NADH  lactic acid + NAD+
Glycolysis: Inputs and Outputs
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Glycolysis
inputs
outputs
glucose
2 pyruvate
2 NADH
2 NAD+
2
ATP
2 ADP
4 ADP + 4 P
4 ATP total
2
19
ATP
net gain
Summary-Aerobic
Cycle
Glycolysis
Krebs
Cycle
Electron
Transport
Chain
Total
Anaerobic
Net ATP
production
2 ATP
Cycle
Net ATP
production
Glycolysis
2 ATP
2 ATP
Fermentation
32 ATP
Glycolysis
2 ATP
Total
Depends on
# of cycles
36 ATP
Glucose Breakdown: Overview of 4 Phases
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NADH
e–
e–
NADH
e–
e–
Cytoplasm
e–
NADH and
FADH2
e–
e–
Glycolysis
Citric acid
cycle
Preparatory reaction
glucose
Mitochondrion
pyruvate
Electron transport
chain and
chemiosmosis
2 ATP
2 ATP
4 ATP total
4 ADP
2
21
ATP
net gain
2 ADP
2
ATP
32 ADP
or 34
32
or 34
ATP
Chemical Equations
Cellular Respiration
O2 + C6H12O6 
CO2
+ H2O + energy
Oxygen + glucose  Carbon Dioxide + Water + ATP
Photosynthesis
CO2 + H2O + energy 
O2 + C6H12O6
Carbon Dioxide + Water + sunlight  Oxygen + glucose
Energy in the biosphere
 Starts with the sun
 Plants take in sunlight and convert the energy
via photosynthesis into sugars. Extra energy is
stored as starches and cellulose.
 Animals eat plants and convert energy into ATP.
Extra energy or calories are stored as glycogen
and fats.
 When animals die, the energy gets released
back to the ecosystem by bacteria digesting the
bodies.
 “Food chain”
Real-life applications
A calorie is how we measure the amount
of energy stored in foods. This is because
it is the extra energy taken by plants from
the sun, or other animals from their food
and stored. Therefore, if you take in more
energy than you are using, you also store
that extra “energy” in glycogen and fat.