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Biology 20 IB
Cellular Respiration Notes
1. Cellular respiration – releases energy stored in
glucose (and other fuel molecules) in a controlled step
by step process that allows the production of ATP
(adenosine triphosphate).
C6H12O6 + 6O2
6CO2 + 6H2O
- fuel molecules are oxidized to form CO2.
- O2 is reduced to form water.
- intermediate electron acceptors used to transfer
electrons (in an electron transport chain) before they
are finally grabbed by O2.
- NAD+ is the is the main electron acceptor molecule
in the ETC.
2. Steps of cellular respiration:
1) Glycolysis - glucose is split (in cytoplasm).
2) Kreb’s cycle - completes oxidation process
- in mitochondrial matrix.
3) Electron transport chain
- step by step energy release for ATP
production.
- includes chemiosmosis.
- across mitochondrial inner membranes.
3. Energy yields:
- occur in two ways:
a. substrate level phosphorylation - ATP
production results directly from breakdown of
substrates (fuel molecules).
b. oxidative phosphorylation – ATP
production due to transfer of electrons from
glucose to O2, via the electron transport
chain and chemiosmosis.
4. Glycolysis: occurs in the cytoplasm
- splitting glucose
- done by ALL cells in some form or another.
- no O2 req’d.
- need glucose
- yields ATP, NADH + H+, pyruvate
Glycolysis
glucose
ATP
ADP
glucose
phosphate
ATP
phosphorylation
of glucose
ADP
fructose
diphosphate
lysis
substrate level
phosphorylation
NAD+
TP
NADH + H+
GP
ADP
ADP
ATP
ATP
ADP
ADP
ATP
ATP
Pyruvate
TP
NAD+
NADH + H+
GP
Pyruvate
Glycolysis summary:
- use 2 ATP, but gain 4 ATP back.
- net yield per glucose:
2 ATP, 2 NADH + H+, 2 pyruvate
(Note: the 2NADH and 2 pyruvate enter the
mitochondria)
5. Kreb’s Cycle: occurs in the mitochondrial matrix:
(draw a mitochondrion:show outer membrane, inner membrane,
cristae, intermembrane space, matrix)
a. the Link-reaction:
-pyruvate is transported by a membrane protein into the
mitochondrion, where it it converted to a 2-carbon acetyl
coenzyme A.
cytoplasm
mitochondrion
transport protein
coenzyme A
acetyl
coenzyme A
pyruvate
CO2
NAD+
NADH + H+
step1: O2 removed (decarboxylation)
step 2: remaining carbons oxidized
(NAD+ reduced to NADH + H+)
step 3: coenzyme A (CoA) is added to form
acetyl CoA (acetyl CoA)
The link reaction yields:
1 CO2
1 NADH + H+
1 acetyl CoA
b. Acetyl CoA enters Kreb’s Cycle:
C3
(pyruvate)
link reaction
C2
C4
CO2
(acetyl CoA)
Kreb’s
Cycle
C5
C6
CO2
One turn of the cycle yields:
2 CO2
3 NADH + H+
1 FADH2
1 ATP (by substrate phosphorylation)
Electron Transport Chains:
 all NADH + H+, and FADH2 are electron carriers.
 electrons are passed from these to other molecules
embedded in the inner membrane of the mitochondria.
 coupled with the ETC is the pumping of H+ from the
matrix across the membrane to the intermembrane
space.
 the accumulated H+ diffuse back to the matrix through
ATP synthase, causing ATP production.
 This is called oxidative phophorylation
NADH + H+
ADP + P
ATP
FADH2
ADP + P
ATP
cytochromes
ADP + P
ATP
H2O
O2
**Each NADH + H+ yields 3 ATP
**Each FADH2 yields 2 ATP
*The terminal electron acceptor IS Arnold
Schwarzenegger, I mean, OXYGEN. And, the final
product formed from the ETC is water.
6. Calculation of total ATP yield during aerobic respiration:
Glycolysis
Link
Reaction
Kreb’s
Cycle
ETC
Total
ATP
X3
X3
X 2**
18
6
4
X2
4
1 GLUCOSE:
2 pyruvate
2 pyruvate:
2 acetyl
CoA
2 acetyl
CoA:
6 NADH + H+
2 NADH +
H+
2 NADH + H+
2 FADH2
2 ATP
(substrate
level
phosphorylation)
2 ATP
(substrate
level
phosphorylation)
2
2
36
ATP
Waste Gas
6 CO2
2 CO2
4 CO2
** it takes two ATP to transfer the electrons from NADH produced by
glycolysis (in the cytoplasm) through the mitochondrial membrane
into the matrix.
Consequently, the total ATP produced by the aerobic respiration of
one glucose is 36.
Even the total of 36 ATP per glucose is an average because the cell
uses energy from the proton gradient in the mitochondria for other
purposes such as the uptake of pyruvate from the cytoplasm.
Further energy summary:
Total yield for each molecule of glucose oxidized
 36 ATP per glucose:
 4 ATP from substrate level phosphorylation
 32 ATP from oxidative phosphorylation-ETC
7. Anaerobic respiration:
 O2 not required
 energy yield much lower
 two types (for you to know):
1. Alcohol fermentation
2. Lactic acid production in muscles
**both are modified forms of glycolysis
8. Alcoholic Fermentation:
glucose
ATP
ADP
glucose
phosphate
ATP
phosphorylation
of glucose
ADP
fructose
diphosphate
lysis
substrate level
phosphorylation
TP
NAD+
NADH + H+
GP
ADP
ADP
ATP
ATP
ADP
ADP
ATP
ATP
Pyruvate
TP
NADH + H+
GP
Pyruvate
NADH + H+
NADH + H+
NAD+
Ethanol + CO2
NAD+
Ethanol + CO2
Summary: - uses 2 ATP, gains back 4 ATP
- reducing pyruvate allows recycling of NAD+
- done by yeast and many bacteria do this.
(wine and beer-making, food spoilage)
Net Yield: - 2 ATP, 2 Ethanol + 2 CO2
NAD+
9. Lactic Acid production by muscles:
glucose
ATP
ADP
glucose
phosphate
ATP
phosphorylation
of glucose
ADP
fructose
diphosphate
lysis
substrate level
phosphorylation
TP
NAD+
NADH + H+
GP
ADP
ADP
ATP
ATP
ADP
ADP
ATP
ATP
Pyruvate
TP
NADH + H+
GP
Pyruvate
NADH + H+
NADH + H+
NAD+
Lactic Acid
NAD+
NAD+
Lactic Acid
Summary: - uses 2 ATP, gains back 4 ATP
- reducing pyruvate allows recycling of NAD+
- done by muscles when an O2 debt exists. (Lactic acid is
carried to liver by blood and converted back to pyruvate.)
- also done by bacteria and yeast (cheese, yogurt)
- results in a burning sensation in muscles
Net Yield: - 2 ATP, 2 lactic acid
NOTE:
 -aerobic respiration is 18X more efficient
(2 ATP vs 36 ATP)
 anaerobic respiration yields about 5% of the
aerobic respiration yield.
10. Other fuel molecules:
Other food molecules can be used for ATP synthesis,
but they may enter the cellular respiration pathways in
different places:
Proteins
Carbohydrates
Amino Acids
Simple sugars
Lipids
Glycerol
Fatty acids
Glycolysis
NH3
(pyruvate)
Acetyl CoA
Kreb’s
Cycle
Electron transport chain
and oxidative phosphorylation
Acetyl CoA plays a central role in food metabolism:
 it is an intermediate in sugar breakdown.
 fatty acids chains are broken into 2-carbon acetyl
groups.
When energy is in short supply an organism will
metabolize:
 simple sugars
 stored complex sugars (glycogen)
 fats
 proteins (as a last resort)
10.



Uses of ATP in the cell include energy for:
chemical reactions (such as protein synthesis)
nerve impulse transmission
mechanical action (muscle contraction and the
motion of flagella and cilia)
 active transport
Ah yes, remember also that the energy conversions of
cellular respiration are not 100%, some energy is lost
as heat.