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Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview: Life Is Work
• Living cells
–
Require transfusions of energy from outside sources to perform
their many tasks
Ex: The giant panda
–
Obtains (chemical, potential) energy for its cells by eating plants
Figure 9.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energy
Flows into an ecosystem as sunlight and leaves
as heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Heat
energy
Review:
• 1st law- Energy cannot be created or destroyed.
Energy can be converted from one form to another.
The sum of the energy before the conversion is equal
to the sum of the energy after the conversion.
• 2nd law- Some usable energy dissipates during
transformations and is lost.
During changes from one form of energy to another,
some usable energy dissipates, usually as heat. The
amount of usable energy therefore decreases.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cellular Respiration
• Glucose + O2  energy (ATP) + CO2 + H2O
• This is exergonic –DG and converts one form of chemical
energy (glucose) into another (ATP), with heat dissipates
– Consumes oxygen and organic molecules (such as
glucose)
– Glucose Oxidation is the most prevalent and efficient
catabolic pathway
– Yields lots of ATP
• An alternate catabolic process, fermentation
– Is a partial degradation of sugars that occurs without
oxygen (in anaerobic conditions)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
More on ATP
• ATP (adenosine triphosphate)
• ATP is a nucleotide. Nucleotides are
the building blocks of nucleic acids such
as DNA and RNA. They contain a
nitrogen-containing base, a 5-carbon
sugar, and phosphate groups.
• The energy in one glucose molecule is
used to produce up to 38 ATP. ATP has
approximately the right amount of energy
for most cellular reactions.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ATP, ADP, AMP
The bonds between the phosphate groups are highenergy bonds. Energy is required (and stored) to
form the bonds and energy is released when the
bonds are broken. (below)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Phosphorylation
• ATP is produced and used continuously. The entire amount of ATP
in an organism is recycled once per minute. Most cells maintain only
a few seconds supply of ATP.
• To keep working, cells must regenerate ATP
• When a phosphate group is transferred to another molecule, it is
called PHOSPHORYLATION.
ADP + Pi + energy ----> ATP
• It takes about 7.3 kcals of energy to phosphorylate ADP into ATP
• Enzyme that catalyzes this reaction is ATP synthase
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Phosphorylation
• Phosphate groups from ATP can also be transferred to other
molecules.
•Enzymes that catalyze this reaction are called KINASES.
•In these phosphorylation reactions, energy is transferred from the
phosphate group in ATP to the phosphorylated compound. This
newly energized compound will participate in other reactions.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Redox Reactions: Oxidation and Reduction
• Catabolic pathways also yield energy due to the
transfer of electrons
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
Cl–
becomes reduced
(gains electron)
•
In oxidation
–
•
A substance loses electrons, or is oxidized
In reduction
–
A substance gains electrons, or is reduced
• “Redox” reactions
– Transfer electrons from one reactant to another
by oxidation and reduction
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“Redox” reactions
Transfer of electrons from one reactant to
another by oxidation and reduction
When the electron moves to a lower energy
level, energy is released.
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Redox cont’d
• Some redox reactions
– Do not completely exchange electrons, instead
they change the degree of electron sharing in
covalent bonds
Products
Reactants
becomes oxidized
+
CH4
CO
2O2
+
Energy
2 H2O
becomes reduced
O
O
C
O
H
O
O
H
H
H
C
+
2
H
H
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Figure 9.3
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Carbon dioxide
Water
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration
– Glucose is oxidized and oxygen is reduced
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
Glucose + Oxygen ----> Carbon dioxide + water + Energy
Yields DG = -686 Kcal/mole
This energy is used to add phosphates to ADP + P  ATP
There is a need to convert glucose (sugar) which is stored chemical
energy into ATP which is usable cell energy
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Electron carriers
• Some compounds can accept and donate electrons
readily, and these are called electron carriers in
organisms. There are a number of molecules that serve
as electron carriers.
– NAD (nicotinamide adenine dinucleotide) is used in
respiration. Reduced to NADH.
– NADP (nicotinamide adenine dinucleotide
phosphate) is another used in photosynthesis.
Reduced to NADPH
– These molecules readily give up electrons (oxidized)
and gain electrons (reduced).
– FAD (flavin adenine dinucleotide) is reduced to
FADH2
– H often represents one electron, one proton.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The electron transport chain
NADH, the reduced form of
NAD+
–
•
•
•
1/
+
2
O2
1/
O2
(from food via NADH)
Passes the electrons
along an electron
transport chain
Electron are passed in a
series of steps instead of in
one explosive reaction
If electron transfer is not
stepwise
–
2H
2 H+ + 2 e–
A large release of
energy occurs =
dangerous to living cells
ATP
ATP
ATP
2 e–
2
Uses the energy from the
electron transfer to form ATP
H+
H2O
Figure 9.5 B
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Controlled
release of
energy for
synthesis of
ATP
Free energy, G
•
(b) Cellular respiration
2
ATP originates in cellular respiration
• What happens is that sugar is broken
down into smaller molecules and
energy is released.
• This energy is used to generate ATP
from ADP and P.
•
Sugar ------> smaller molecules--------->ADP + Pi ------> ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Stages of Cellular Respiration: A Preview
Respiration is a cumulative function of three
metabolic stages
• Glycolysis
– Breaks down glucose into two molecules of pyruvate
• The citric acid (Krebs) cycle
– Completes the breakdown of glucose
• Oxidative phosphorylation
– Is driven by the electron transport chain (ETC)
– Generates ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Figure 9.6
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Substrate-level
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
• Both glycolysis and the citric acid cycle
– Can generate ATP by substrate-level
phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Figure 9.7
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Product
ATP
Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate
Glycolysis
– Means “splitting of sugar”
– Breaks down glucose into pyruvate
– Occurs in the cytoplasm of the cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis consists of two major phases
– Energy investment phase
Citric
acid
cycle
Glycolysis
– Energy payoff phase
Oxidative
phosphorylation
ATP
ATP
ATP
Energy investment phase
Glucose
2 ATP + 2 P
2 ATP
used
Energy payoff phase
4 ADP + 4 P
exergonic, energy liberating DG
2 NAD+ + 4 e- + 4 H
+
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
endergonic, energy intake +DG
Glucose
4 ATP formed – 2 ATP used
Figure 9.8
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 NAD+ + 4 e– + 4 H
+
2 Pyruvate + 2 H2O
2 ATP + 2 H+
2 NADH
A closer look at the energy investment phase:
[Step 1] Energy input required
Terminal P from an ATP (-->ADP) is bonded to the C6 of a glucose
DG = - 3.3 (enzyme: hexokinase)
[Step 2] glucose - 6 - phosphate------> fructose-6-phosphate
•atoms rearranged
DG = + 0.4 (enzyme: phosphoglucoisomerase)
CH2OH
HH
H
HO H
HO
OH
H OH
Glycolysis
Glucose
ATP
1
Hexokinase
ADP
[Step 3] fructose-6-phosphate------> fructose 1,6 biphosphate
•Phosphate added to C1
DG = - 3.4 (enzyme: phosphofructokinase)
• splits into two products
[Step 4] fructose -1, 6 - biphosphate---> dihydroxyacetone phosphate
AND glyceraldehyde phosphate*
DG = + 5.7 ( enzyme: aldolase)
•Our 6-carbon sugar is split into TWO 3-carbon products
[Step 5] *Ultimately, all of the dihydroxyacetone phosphate will be
converted into glyceraldehyde-3-phosphate, so each step is actually x 2
from here (because each of the two molecules will proceed through
Steps 5- 9 )
dihydroxyacetone phosphate-------> glyceraldehyde-3-phosphate
(enzyme: isomerase)
CH2OH P
HH OH
OH H
HO
H OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
CH2O P
O CH2OH
H HO
HO
H
HO H
Fructose-6-phosphate
ATP
3
Phosphofructokinase
ADP
P O CH2 O CH2 O P
HO
H
OH
HO H
Fructose1, 6-bisphosphate
4
Aldolase
5
H
P O CH2 Isomerase
C O
C O
CHOH
CH2OH
CH2 O P
Figure 9.9 A
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Citric
Oxidative
acid
cycle phosphorylation
A closer look at the energy payoff phase
[Step 6]
2 Glyceraldehyde-3-phosphate molecules are then oxidized
•
2 hydrogens (with e-) are removed, and NAD+ is reduced to NADH and H+
•
Also, a free phosphate attaches to each of the glyceraldehyde-3-phosphates
2 Glyceraldehyde-3-phosphate---------------> 1, 3 biphosphoglycerate (x2)
P
•
Pi = free phosphates, not taken from another molecule such as ATP
•
NAD = nicotinamide adenine dinucleotide (niacin derivative)
DG = + 1.5
(enzyme: triose phosphate dehydrogenase)
[Step 7] a P is released from each 1,3 biphosphoglycerate molecule and is used to "recharge" 2 ADPs----> 2 ATPs
thus, converting the 1,3 biphosphoglycerate to 3-phosphoglycerate
O C O
CHOH
CH2 O P
1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
O–
2
C
CHOH
(highly exergonic= large DG to pull preceding reactions forward)
(x2) 1,3 Diphosphoglycerate-----------------------------> 3-phosphoglycerate
ADP---> ATP
DG = -4.5
2 Pi
2 NADH
+ 2 H+
2
NAD+ is reduced to NADH and H+
6
Triose phosphate
dehydrogenase
2 NAD+
(enzyme: phosphoglycerokinase)
CH2 O P
3-Phosphoglycerate
8
Phosphoglyceromutase
2
O–
C
(x 2) [Step 8] The remaining P group is enzymatically transferred from the 3C to
P
CH2OH
2-Phosphoglycerate
9
Enolase
2H O
the 2C
3- phosphoglycerate-----------------------> 2 - phosphoglycerate
DG = + 1.0
O
H C O
2
(enzyme: phosphoglyceromutase)
2
O–
C O
C O
(x 2) [Step 9] A molecule of H2O removed
2 - phosphoglycerate----------------> phosphoenolpyruvate
- H2O
Pyruvate kinase
DG = + 0.4 (enzyme: enolase)
2 ATP
2
O–
C O
(x 2) [Step 10] Another phosphate P is transferred to ADP
C O
( highly exergonic, pulls 2 preceding rxns!!!)
phosphoenolpyruvate--------------------> pyruvate (pyruvic acid)
P
CH2
Phosphoenolpyruvate
2 ADP
10
DG = - 7.5 ( enzyme: pyruvate kinase)
ADP---> ATP
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CH3
Pyruvate
Mitochondria Review
•
The mitochondrion is surrounded by two membranes. The outer is smooth and the
inner folds inwards. The inner folds are called cristae. Within the inner compartment
of the mitochondrion, surrounding the cristae, there is a dense solution known as the
matrix. The matrix contains enzymes, co-enzymes, water, phosphates, and other
molecules needed in respiration.
•
The outer membrane is permeable to most small molecules, but the inner one
permits the passage of only certain molecules, such as pyruvic acid and ATP.
•
Proteins are built into the membrane of the cristae. These proteins are involved with
the Electron Transport Chain. The inner membrane is about 80% protein and 20%
lipids. 95% of the ATP generated by the heterotrophic cell is produced by the
mitochondrion.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Fate of the Pyruvate
• The pyruvate passes from the cytoplasm (where its
produced thru glycolysis) and crosses the outer & inner
membranes of the mitochondria
• Before entering the Krebs Cycle, the 3-C pyruvate
molecule is oxidized: the carbon and oxygen atoms of the
carboxyl group are removed (into CO2) and a 2-C acetyl
group is left (CH3CO)
• In the course of this rxn, the carboxyl hydrogen reduces a
molecule of NAD+ to NADH
• The acetyl is momentarily accepted by a "coenzyme A"
molecule (a large, complex molecule formed from
pantothenic acid (vitamin B)), forming Acetyl-CoA
• From here the Acetyl CoA can enter the Krebs (aka, Citric
Acid) Cycle. Acetyl CoA moves into the mitochondria
and is completely dismantled by the enzymes in the
mitochondria.
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• Before the citric acid cycle can begin
– Pyruvate must first be converted to acetyl CoA,
which links the cycle to glycolysis
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
O–
S
CoA
C
O
2
C
C
O
O
1
3
CH3
Pyruvate
Transport protein
Figure 9.10
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CH3
Acetyle CoA
CO2
Coenzyme A
An overview of the citric acid cycle
• Discovered 1937 by British
biochemist Sir Hans Adolf Krebs
•
• CO2 is produced.
Pyruvate
(from glycolysis,
2 molecules per glucose)
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
• Acetyls are dismantled and
reconfigured. The electrons are
what's important.
CoA
NADH
+ 3 H+ Acetyle CoA
CoA
CoA
• The Krebs's cycle only gives us two
molecules of ATP. Added with the two
molecules of ATP made in Glycolysis,
the total is now a meager four
molecules of ATP.
•The remainder of the ATPs come
from the Electron Transport System,
which takes the electrons produced in
the Krebs's cycle and makes ATP.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Citric
acid
cycle
2 CO2
3 NAD+
FADH2
FAD
3 NADH
+ 3 H+
ADP + P i
ATP
Figure 9.11
A closer look at the citric acid cycle
In general:
Citric
• 2-C acetyl combines with 4-C oxaloacetic acid toGlycolysis
Oxidative
acid phosphorylation
cycle
form a 6-C citric acid.
• Two carbons (per cycle) are oxidized to CO2 which
S CoA
regenerates a molecule of oxaloacetic acid
C O
• Each turn of the cycle uses up one acetyl group
CH
Acetyl
CoA
and regenerates a oxaloacetic acid, then begins the
CoA SH
cycle again.
O C COO
• Energy is released by breaking C-H and C-C
NADH
COO
CH
1
+H
bonds and is stored by transforming ADP to ATP (1
CH
COO
+
NAD
8 Oxaloacetate HO C COO
molecule per turn of the cycle) and to convert NAD+
CH
COO
to NADH and H+ (3x per cycle)
COO
HO CH
Citrate
• Also, FAD (flavin adenine dinucleotide) is
Figure 9.12 CH Malate
COO
converted to FADH2 (one molecule per cycle)
Citric
1. No oxygen is required in Krebs Cycle
acid
7
cycle
2. All e- and p+ are accepted by either NAD+ or FAD H2O
COO
3
–
–
+
H2O
2
–
COO–
2
–
–
CH2
2
HC COO–
2
–
HO
CH
COO–
2
Isocitrate
–
CO2
3
NAD+
–
CH
• There are 8 steps in the cycle and the aim is to
totally dismantle the Acetyl CoA, using only its
electrons.
• We have totally taken apart the glucose molecule.
• Only four ATPs have resulted, 2 from glycolysis
and 2 from the CAC.
• But we still have a lot of ELECTRONS captured in
the form of NADH and FADH2 = potential energy
Fumarate
HC
CH2
CoA SH
6
CoA SH
COO–
FAD
CH2
CH2
COO–
C O
Succinate
Pi
S
CoA
GTP GDP Succinyl
CoA
ADP
ATP
4
C O
COO–
CH2
5
CH2
FADH2
COO–
NAD+
NADH
+ H+
NADH
+ H+
a-Ketoglutarate
CH2
COO–
Figure 9.12
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COO–
CO2
Oxidative phosphorylation
• Concept 9.4: During oxidative phosphorylation,
chemiosmosis couples electron transport to
ATP synthesis
• NADH and FADH2
– Donate electrons to the electron transport
chain, which powers ATP synthesis via
oxidative phosphorylation
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The Pathway of Electron Transport
In the electron transport chain
Electrons from NADH and FADH2 lose energy
in several steps
At the end of the chain
Electrons are passed to oxygen, forming water
NADH
50
electrons are "passed down" a "staircase" of
cytochromes and the energy released in
lowering the energy level is stored in
additional ATP molecules...called
Oxidative Phosphorylation
remember, the energy from lowering electrons
can do this: ADP + P = ATP
FADH2
Free energy (G) relative to O2 (kcl/mol)
Transport Chain carriers are called
CYTOCHROMES (consist of protein and
a heme group = atom of iron enclosed in
a porphyrin ring (note the similarity to
hemoglobin!)
40
FMN
I
Fe•S
Fe•S II
O
30
20
Multiprotein
complexes
FAD
III
Cyt b
Fe•S
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
10
0
2 H + + 12 O2
e-
---> for every
passed down the chain from
NADH, 3 ATPs are formed
Figure 9.13
---> for every 2e- from FADH2, 2 ATP's are
formed
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H2 O
Chemiosmosis: The Energy-Coupling Mechanism
• ATP synthase
– Is the enzyme that actually makes ATP
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
clockwise when
H+ flows past
it down the H+
gradient.
A stator anchored
in the membrane
holds the knob
stationary.
H+
ADP
+
Pi
Figure 9.14
MITOCHONDRIAL MATRIX
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ATP
A rod (for “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
Three catalytic
sites in the
stationary knob
join inorganic
Phosphate to ADP
to make ATP.
Chemiosmosis
Is an energy-coupling
mechanism that uses
energy in the form of a
H+ gradient across a
membrane to drive
cellular work
At certain steps along the
electron transport
chain, electron transfer
causes protein
complexes to pump H+
from the mitochondrial
matrix to the
intermembrane space
The resulting H+ gradient
•
Stores energy
•
Drives chemiosmosis
in ATP synthase
•
Is referred to as a
“proton-motive force”
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• Chemiosmosis and the electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane
ATP
ATP
H+
H+
H+
Intermembrane
space
Protein complex
of electron
carners
Q
I
Inner
mitochondrial
membrane
IV
III
ATP
synthase
II
FADH2
NADH+
Mitochondrial
matrix
H+
Cyt c
FAD+
NAD+
2 H+ + 1/2 O2
H2O
ADP +
(Carrying electrons
from, food)
ATP
Pi
H+
Chemiosmosis
Electron transport chain
+
ATP
synthesis
powered by the flow
Electron transport and pumping of protons (H ),
+
+
which create an H gradient across the membrane Of H back across the membrane
Figure 9.15
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Oxidative phosphorylation
Summary
• There are three main processes in this
metabolic enterprise
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
6 NADH
Citric
acid
cycle
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
+ 2 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP
Figure 9.16
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The energy tally sheet
Glycolysis:
2 ATP
2 NADH ets 
Oxidation: pyruvate  acetyl CoA 
CAC/Krebs
=2 ATP
6 ATP
=6 ATP
1 NADH  ets  3 ATP (x2)
= 6 ATP
x2 turns

2 ATP
3 NADH  ets  9 ATP x2 turns

18 ATP
1 FADH2  ets  2 ATP x2 turns

4 ATP
1 ATP
= 24 ATP
TOTAL = 38 ATP
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efficiency
• Less than 40% of the energy in a glucose
molecule is transferred to ATP during cellular
respiration, making approximately 38 ATP
DG =
ADP + Pi --> ATP
= about 7 kcal/mole
X 38 = 266 kcal/mole (captured in P bonds)
DG = -686 kcal/mole (free energy change during glycolysis and
oxidation for glucose)
= about 39% efficiency
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
FERMENTATION
• Concept 9.5: Fermentation enables some
cells to produce ATP without the use of
oxygen
• Oxidative cellular respiration
– Relies on oxygen to produce ATP
– Involves Krebs cycle and ETS
• In the absence of oxygen
– Cells can still produce a little bit of ATP
through fermentation
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Without oxygen:
• Glycolysis
– Can produce ATP with or without oxygen,
in either aerobic or anaerobic conditions
– Pyruvate is produced, some ATP is made
In anaerobic respiration (fermentation) pyruvate
must be processed in the absence of oxygen
• The breakdown of the sugar still takes place
through a series of chemical reactions, but
with a different outcome.
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The Evolutionary Significance of Glycolysis
• Glycolysis
– Occurs in the cytoplasm of nearly all
organisms
– Probably evolved in ancient prokaryotes
before there was oxygen in the
atmosphere
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• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Acetyl CoA
Citric
acid
cycle
Fermentation
• Living organisms have developed numerous and
different fermentation pathways; however, most
organisms use the following Embden-Meyerhoff
pathway, named for the two discoverers.
• The pyruvate can take two pathways in anaerobic
respiration:
– a. Pyruvate will be converted to ethyl alcohol
(ethanol) and carbon dioxide. This is called alcoholic
fermentation and is the basis of our wine, beer and
liquor industry.
– b. The pyruvate will be converted to lactic acid. This
is called lactic acid fermentation. Lactic acid is what
makes your muscles burn during prolonged
exercise, this process is also used to make yogurt.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Types of Fermentation
• Fermentation consists of
– Glycolysis plus reactions that regenerate
NAD+, which can be reused by glyocolysis
• In alcohol fermentation
– Pyruvate is converted to ethanol in two steps,
one of which releases CO2
• During lactic acid fermentation
– Pyruvate is reduced directly to NADH to form
lactate as a waste product
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 ADP + 2
P1
2 ATP
O–
C O
Glucose
Glycolysis
C O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
2 CO2
H
H C OH
C O
CH3
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
2 ATP
Glycolysis
O–
C O
C O
O
2 NAD+
2 NADH
CH3
C O
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
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Fermentation and Cellular Respiration Compared
• Both fermentation and cellular respiration
– Use glycolysis to oxidize glucose and other
organic fuels to pyruvate
• Fermentation and cellular respiration
– Differ in their final electron acceptor
• Oxidative cellular respiration
– Produces more ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Versatility of Catabolism
• Concept 9.6: Glycolysis and the citric acid
cycle connect to many other metabolic
pathways
• Catabolic pathways
– Funnel electrons from many kinds of organic
molecules into cellular respiration
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The catabolism of various molecules from food
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Figure 9.19
Oxidative
phosphorylation
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Fatty
acids
Regulation of Cellular Respiration via Feedback
Mechanisms
• Cellular respiration
– Is controlled by allosteric enzymes at key
points in glycolysis and the citric acid cycle
Enzyme 1
A
Enzyme 2
D
C
B
Reaction 1
Enzyme 3
Reaction 2
Starting
molecule
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Reaction 3
Product
Feedback Control Regulates Biological Processes
• The control of cellular respiration
Glucose
Glycolysis
Fructose-6-phosphate
–
Inhibits
AMP
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
Citrate
ATP
Acetyl CoA
Citric
acid
cycle
Figure 9.20
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Oxidative
phosphorylation