Transcript Citric acid cycle

LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 9
Cellular Respiration and
Fermentation
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Life Is Work
• Living cells require energy from outside
sources
• Some animals, such as the chimpanzee, obtain
energy by eating plants, and some animals
feed on other organisms that eat plants
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• Energy flows into
an ecosystem as
sunlight and
leaves as heat
• Photosynthesis
generates O2 and
organic
molecules, which
are used in
cellular
respiration
• Cells use
chemical energy
stored in organic
molecules to
regenerate ATP,
which powers
work
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2  H2O
Cellular respiration
in mitochondria
ATP
Heat
energy
Organic
 O2
molecules
ATP powers
most cellular work
Concept 9.1: Catabolic pathways yield
energy by oxidizing organic fuels
• Several processes are central to cellular
respiration and related pathways
• Ch. 8: Metabolic pathways that release stored
by breaking down complex molecules are
called catabolic pathways.
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Catabolic Pathways and Production of ATP
• Organic compounds possess potential energy as a
result of the arrangement of the electrons in the
bonds between their atoms.
• The breakdown of organic molecules is exergonic
(Exergonic = ???)
• Compounds that can participate in exergonic
reactions can act as fuels.
• With the help of enzymes, a cell breaks down
complex molecules that are rich in potential energy
to simpler waste products that have less energy
• Some of the energy taken out of chemical storage
can be used to do work; the rest is lost as heat.
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Catabolic Pathways and Production of ATP
• Organic compounds possess potential energy as a
result of the arrangement of the electrons in the
bonds between their atoms.
• The breakdown of organic molecules is exergonic
(Exergonic = "releasing energy in the form of work")
• Compounds that can participate in exergonic
reactions can act as fuels.
• With the help of enzymes, a cell breaks down
complex molecules that are rich in potential energy
to simpler waste products that have less energy
• Some of the energy taken out of chemical storage
can be used to do work; the rest is lost as heat.
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Catabolic Pathways and Production of ATP
• Fermentation is a partial degradation of
sugars that occurs without O2
• Aerobic respiration consumes organic
molecules and O2 and yields ATP
– Most efficient and prevalent
– Greek: Aer = air and bios = life
• Anaerobic respiration is similar to aerobic
respiration but consumes compounds other
than O2
– An = without
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• Cellular respiration includes both aerobic and
anaerobic respiration but is often used to refer to
aerobic respiration
• Organic compounds + Oxygen  Carbon Dioxide + Water + Energy
• Although carbohydrates, fats, and proteins are all
consumed as fuel, it is helpful to trace cellular
respiration with the sugar glucose
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
• The breakdown of glucose is exergonic
• What does a negative ΔG mean?
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Redox Reactions: Oxidation and Reduction
• The transfer of electrons during chemical
reactions releases energy stored in organic
molecules
• This released energy is ultimately used to
synthesize ATP
– ATP ADP + P
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The Principle of Redox
• How do the catabolic pathways that breakdown
glucose and other organic fuels give off energy?
– The relocation of electrons during chemical reactions
releases stored energy stored in organic molecules, and
this energy ultimately is used to synthesize ATP.
• Chemical reactions that transfer electrons between
reactants are called oxidation-reduction reactions,
or redox reactions
• In oxidation, a substance loses electrons, or is
oxidized
• In reduction, a substance gains electrons, or is
reduced (the amount of positive charge is reduced)
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Figure 9.UN01
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
Figure 9.UN02
becomes oxidized
becomes reduced
• The electron donor is called the reducing
agent
• The electron receptor is called the oxidizing
agent
• Some redox reactions do not transfer electrons
but change the electron sharing in covalent
bonds
• An example is the reaction between methane
and O2
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Figure 9.UN02
Reducing Agent?
becomes oxidized
becomes reduced
Oxidizing Agent?
Figure 9.3
Reactants
Products
becomes oxidized
Energy
becomes reduced
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Carbon and Oxygen still have the same
number of electrons.
Water
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration, the fuel (such as
glucose) is oxidized, and O2 is reduced
• Organic molecules have an abundance of
hydrogen—their bonds are a source of electrons
whose energy may be released as the electrons
are transferred to oxygen.
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Figure 9.UN03
becomes oxidized
becomes reduced
Stepwise Energy Harvest via NAD+ and the
Why steps?
Electron Transport Chain
• In cellular respiration, glucose and other organic
molecules are broken down in a series of steps
• The hydrogen atoms are not transferred directly to
oxygen, but instead are usually passed to an electron
carrier—NAD+
• Electrons from organic compounds are usually first
transferred to NAD+, a coenzyme
• As an electron acceptor, NAD+ functions as an
oxidizing agent during cellular respiration
• Each NADH (the reduced form of NAD+) represents
stored energy that is tapped to synthesize ATP
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Figure 9.4
NAD
NADH
Dehydrogenase
Reduction of NAD
(from food)
Nicotinamide
(oxidized form)
Oxidation of NADH
Nicotinamide
(reduced form)
Figure 9.UN04
Dehydrogenase
NAD+ is reduced to NADH
Reduce: gain electrons or the
amount of positive charge is reduced
• NADH passes the electrons to the electron
transport chain
• Unlike an uncontrolled reaction, the electron
transport chain passes electrons in a series of
steps instead of one explosive reaction
• O2 pulls electrons down the chain in an energyyielding tumble
• The energy yielded is used to regenerate ATP
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Figure 9.5
H2  1/2 O2

2H
1/
Explosive
release of
heat and light
energy
Free energy, G
Free energy, G
(from food via NADH)
Controlled
release of
+

2H  2e
energy for
synthesis of
ATP
O2
ATP
ATP
ATP
2 e
2
1/
H+
H2O
(a) Uncontrolled reaction
2
H2O
(b) Cellular respiration
2
O2
The Stages of Cellular Respiration:
A Preview
• Harvesting of energy from glucose has three
stages
– Glycolysis (breaks down glucose into two
molecules of pyruvate)
– The citric acid cycle (completes the
breakdown of glucose)
– Oxidative phosphorylation (accounts for
most of the ATP synthesis)
© 2011 Pearson Education, Inc.
Figure 9.UN05
1. Glycolysis (color-coded teal throughout the chapter)
2. Pyruvate oxidation and the citric acid cycle
(color-coded salmon)
3. Oxidative phosphorylation: electron transport and
chemiosmosis (color-coded violet)
Figure 9.6-1
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
ATP
Substrate-level
phosphorylation
MITOCHONDRION
During glycolysis, each glucose
molecule is broken down into two
molecules of pyruvate. It enters
the mitochondrion.
Figure 9.6-2
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
MITOCHONDRION
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Pyruvate is oxidized to acetyl
CoA, which is further
oxidized to CO2 in the citric
acid cycle. NADH and a
similar electron carrier,
FADH2, transfer electrons
derived from glucose to
electron transport chains,
which are built into the inner
mitochondrial membrane. .
Figure 9.6-3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
CYTOSOL
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
During oxidative phosphorylation, electron transport chains convert
the chemical energy to a form used for ATP synthesis in the process
called chemiosmosis.
• The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
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BioFlix: Cellular Respiration
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• Oxidative phosphorylation accounts for almost
90% of the ATP generated by cellular
respiration
• A smaller amount of ATP is formed in glycolysis
and the citric acid cycle by substrate-level
phosphorylation
• For each molecule of glucose degraded to CO2
and water by respiration, the cell makes up to
32 molecules of ATP
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Figure 9.7
Enzyme
Enzyme
ADP
P
Substrate
ATP
Product
Concept 9.2: Glycolysis harvests chemical
energy by oxidizing glucose to pyruvate
• Glycolysis (“splitting of sugar”) breaks down
glucose into two molecules of pyruvate
• Glycolysis occurs in the cytoplasm and has two
major phases
– Energy investment phase
– Energy payoff phase
• Glycolysis occurs whether or not O2 is present
• All the carbon originally present in glucose is
accounted for in the two molecules of pyruvate, no
carbon is released (CO2)
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Figure 9.8
Energy Investment Phase
Glucose
2 ADP  2 P
2 ATP used
Energy Payoff Phase
4 ADP  4 P
2 NAD+  4 e  4 H+
4 ATP formed
2 NADH  2 H+
2 Pyruvate  2 H2O
Net
Glucose
4 ATP formed  2 ATP used
2 NAD+  4 e  4 H+
2 Pyruvate  2 H2O
2 ATP
2 NADH  2 H+
Glycolysis is
a source of
ATP and
NADH!
Figure 9.9a
Glycolysis: Energy Investment Phase
Glucose
ATP
Fructose 6-phosphate
Glucose 6-phosphate
ADP
Hexokinase
1
Phosphoglucoisomerase
2
1. Add a P
2. Isomerize
Figure 9.9b
Glycolysis: Energy Investment Phase
Fructose 6-phosphate
ATP
Fructose 1,6-bisphosphate
ADP
Phosphofructokinase
3
3. Adds another P
4. Breaks the sugar
into 2
5. Reversible
conversion
Aldolase
Dihydroxyacetone
phosphate
4
Glyceraldehyde
3-phosphate
Isomerase
5
To
step 6
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
+ 2 H
2 ADP
2
2
Triose
phosphate
dehydrogenase
6
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
7
3-Phosphoglycerate
6. 2 reactions. Sugar is oxidized by the transfer of electrons to NAD+ and
forming NADH. Second, the energy released from this exergonic redox
reaction is used to attach a P to the oxidized substrate, making a product of
very high potential energy
7. P is transferred to ADP in an exergonic reaction.
Figure 9.9d
Glycolysis: Energy Payoff Phase
2 H2O
2
2
8
2 ADP
2
Phosphoglyceromutase
3-Phosphoglycerate
2 ATP
Pyruvate
kinase
Enolase
2-Phosphoglycerate
9
2
Phosphoenolpyruvate (PEP)
10
Pyruvate
8. Relocation of the P group
9. Double bond formed by extracting water
10. P group is transferred from PEP to ADP and pyruvate is
formed. m
Concept 9.3: After pyruvate is oxidized, the
citric acid cycle completes the energyyielding oxidation of organic molecules
• In the presence of O2, pyruvate enters the
mitochondrion (in eukaryotic cells) where the
oxidation of glucose is completed
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Oxidation of Pyruvate to Acetyl CoA
• Before the citric acid cycle can begin, pyruvate
must be converted to acetyl Coenzyme A
(acetyl CoA), which links glycolysis to the citric
acid cycle
• This step is carried out by a multienzyme
complex that catalyses three reactions
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Figure 9.10
Figure 9.10 Oxidation of pyruvate to acetyl
CoA, the step before the citric acid cycle.
MITOCHONDRION
CYTOSOL
CO2
Coenzyme A
3
1
2
Pyruvate
NAD
NADH + H
Acetyl CoA
Transport protein
Pyruvate is a charged molecule, so it must enter the mitochondrion via active transport,
with the help of a transport protein. A complex of several enzymes catalyzes 3 steps.
The acetyl group of acetyl CoA will enter the citric acid cycle. The CO2 molecule will
diffuse out of the cell. S-CoA is attached to a molecule (S for sulfur atom)
The Citric Acid Cycle
• The citric acid cycle, also called the Krebs
cycle, completes the break down of pyruvate
to CO2
• The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1
FADH2 per turn
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Figure 9.11
Pyruvate
CO2
NAD
CoA
NADH
+ H
Acetyl CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD
FADH2
3 NADH
FAD
+ 3 H
ADP + P i
ATP
• The citric acid cycle has eight steps, each
catalyzed by a specific enzyme
• The acetyl group of acetyl CoA joins the cycle
by combining with oxaloacetate, forming citrate
• The next seven steps decompose the citrate
back to oxaloacetate, making the process a
cycle
• The NADH and FADH2 produced by the cycle
relay electrons extracted from food to the
electron transport chain
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Figure 9.12-1
Acetyl CoA
CoA-SH
1
Oxaloacetate
Citrate
Citric
acid
cycle
Figure 9.12-2
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric
acid
cycle
Figure 9.12-3
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
3
NADH
+ H
CO2
-Ketoglutarate
Figure 9.12-4
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
NAD
NADH
Succinyl
CoA
+ H
CO2
Figure 9.12-5
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
CoA-SH
5
NAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Figure 9.12-6
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Figure 9.12-7
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Figure 9.12-8
Acetyl CoA
CoA-SH
NADH
+ H
H2O
1
NAD
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Concept 9.4: During oxidative
phosphorylation, chemiosmosis couples
electron transport to ATP synthesis
• Following glycolysis and the citric acid cycle,
NADH and FADH2 account for most of the
energy extracted from food
• These two electron carriers donate electrons to
the electron transport chain, which powers ATP
synthesis via oxidative phosphorylation
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The Pathway of Electron Transport
• The electron transport chain is in the inner
membrane (cristae) of the mitochondrion
• Most of the chain’s components are proteins,
which exist in multiprotein complexes
• The carriers alternate reduced and oxidized
states as they accept and donate electrons
• Electrons drop in free energy as they go down
the chain and are finally passed to O2, forming
H2O
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Figure 9.13
NADH
50
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
Each
component of
the chain
becomes
reduced when it
accepts
electrons from
its uphill
neighbor, which
has a lower
affinity for
electrons. It
then returns to
its oxidized
form as It
passes
electrons to its
downhill more
electronegative
neighbor.
2 e
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
• Electrons are transferred from NADH or FADH2
to the electron transport chain
• Electrons are passed through a number of
proteins including cytochromes (each with an
iron atom) to O2
• The electron transport chain generates no ATP
directly
• It breaks the large free-energy drop from food
to O2 into smaller steps that release energy in
manageable amounts
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Chemiosmosis: The Energy-Coupling
Mechanism
• Electron transfer in the electron transport chain
causes proteins to pump H+ from the
mitochondrial matrix to the intermembrane space
• H+ then moves back across the membrane,
passing through the proton, ATP synthase
• ATP synthase uses the exergonic flow of H+ to
drive phosphorylation of ATP
• This is an example of chemiosmosis, the use of
energy in a H+ gradient to drive cellular work
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Figure 9.14
Figure 9.14 ATP synthase, a molecular mill.
INTERMEMBRANE SPACE
H
Stator
Rotor
Internal
rod
Catalytic
knob
ADP
+
Pi
ATP
MITOCHONDRIAL MATRIX
1. H+ ions flowing down their gradient
enter a half channel in a stator, which
is anchored in the membrane.
2. H+ ions enter binding sites within a
rotor changing the shape of each
subunit that the rotor spins within the
membrane
3. Each H+ ion makes one complete
turn before leaving the rotor and
passing through a second half
channel in the stator into the
mitochondrial matrix
4. Spinning of the rotor causes an
internal rod to spin as well. This rod
extends like a stalk into the knob
below it, which is held stationary by
part of the stator.
5. Turning of the rod activates catalytic
sites in the knob that produce ATP
from ADP and P
Figure 9.15
H
H

H
Protein
complex
of electron
carriers
Cyt c
Q
I
IV
III
II
FADH2 FAD
NADH
H
2 H + 1/2O2
ATP
synthase
H2O
NAD
ADP  P i
(carrying electrons
from food)
ATP
H
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis
• The energy stored in a H+ gradient across a
membrane couples the redox reactions of the
electron transport chain to ATP synthesis
• The H+ gradient is referred to as a protonmotive force, emphasizing its capacity to do
work
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An Accounting of ATP Production by
Cellular Respiration
• During cellular respiration, most energy flows
in this sequence:
glucose  NADH  electron transport chain
 proton-motive force  ATP
• About 34% of the energy in a glucose molecule
is transferred to ATP during cellular respiration,
making about 32 ATP
• There are several reasons why the number of
ATP is not known exactly
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Figure 9.16
Electron shuttles
span membrane
2 NADH
Glycolysis
2 Pyruvate
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
CYTOSOL
6 NADH
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
Concept 9.5: Fermentation and anaerobic
respiration enable cells to produce ATP
without the use of oxygen
• Most cellular respiration requires O2 to produce
ATP
• Without O2, the electron transport chain will
cease to operate
• In that case, glycolysis couples with
fermentation or anaerobic respiration to
produce ATP
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• Anaerobic respiration uses an electron
transport chain with a final electron acceptor
other than O2, for example sulfate
• Fermentation uses substrate-level
phosphorylation instead of an electron
transport chain to generate ATP
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Types of Fermentation
• Fermentation consists of glycolysis plus
reactions that regenerate NAD+, which can be
reused by glycolysis
• Two common types are alcohol fermentation
and lactic acid fermentation
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• In alcohol fermentation, pyruvate is converted
to ethanol in two steps, with the first releasing
CO2
• Alcohol fermentation by yeast is used in
brewing, winemaking, and baking
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Animation: Fermentation Overview
Right-click slide / select “Play”
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Figure 9.17
2 ADP  2 P
Glucose
i
2 ADP  2 P
2 ATP
Glycolysis
Glucose
i
2 ATP
Glycolysis
2 Pyruvate
2 NAD 
2 Ethanol
(a) Alcohol fermentation
2 NADH
 2 H
2 NAD 
2 CO2
2 Acetaldehyde
2 NADH
 2 H
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
Figure 9.17a
2 ADP  2 P i
Glucose
2 ATP
Glycolysis
2 Pyruvate
2 NAD 
2 Ethanol
(a) Alcohol fermentation
2 NADH
 2 H
2 CO2
2 Acetaldehyde
• In lactic acid fermentation, pyruvate is reduced
to NADH, forming lactate as an end product,
with no release of CO2
• Lactic acid fermentation by some fungi and
bacteria is used to make cheese and yogurt
• Human muscle cells use lactic acid
fermentation to generate ATP when O2 is
scarce
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Figure 9.17b
2 ADP  2 P i
Glucose
2 ATP
Glycolysis
2 NAD 
2 NADH
 2 H
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
Comparing Fermentation with Anaerobic
and Aerobic Respiration
• All use glycolysis (net ATP = 2) to oxidize glucose
and harvest chemical energy of food
• In all three, NAD+ is the oxidizing agent that
accepts electrons during glycolysis
• The processes have different final electron
acceptors: an organic molecule (such as pyruvate
or acetaldehyde) in fermentation and O2 in cellular
respiration
• Cellular respiration produces 32 ATP per glucose
molecule; fermentation produces 2 ATP per
glucose molecule
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• Obligate anaerobes carry out fermentation or
anaerobic respiration and cannot survive in the
presence of O2
• Yeast and many bacteria are facultative
anaerobes, meaning that they can survive
using either fermentation or cellular respiration
• In a facultative anaerobe, pyruvate is a fork in
the metabolic road that leads to two alternative
catabolic routes
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Figure 9.18
Glucose
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol,
lactate, or
other products
Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Ancient prokaryotes are thought to have used
glycolysis long before there was oxygen in the
atmosphere
• Very little O2 was available in the atmosphere
until about 2.7 billion years ago, so early
prokaryotes likely used only glycolysis to
generate ATP
• Glycolysis is a very ancient process
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Concept 9.6: Glycolysis and the citric acid
cycle connect to many other metabolic
pathways
• Gycolysis and the citric acid cycle are major
intersections to various catabolic and anabolic
pathways
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The Versatility of Catabolism
• Catabolic pathways funnel electrons from many
kinds of organic molecules into cellular
respiration
• Glycolysis accepts a wide range of
carbohydrates
• Proteins must be digested to amino acids;
amino groups can feed glycolysis or the citric
acid cycle
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• Fats are digested to glycerol (used in
glycolysis) and fatty acids (used in generating
acetyl CoA)
• Fatty acids are broken down by beta oxidation
and yield acetyl CoA
• An oxidized gram of fat produces more than
twice as much ATP as an oxidized gram of
carbohydrate
© 2011 Pearson Education, Inc.
Figure 9.19
Proteins
Carbohydrates
Amino
acids
Sugars
Glycolysis
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Fats
Glycerol Fatty
acids
Biosynthesis (Anabolic Pathways)
• The body uses small molecules to build other
substances
• These small molecules may come directly
from food, from glycolysis, or from the citric
acid cycle
© 2011 Pearson Education, Inc.
Regulation of Cellular Respiration via
Feedback Mechanisms
• Feedback inhibition is the most common
mechanism for control
• If ATP concentration begins to drop,
respiration speeds up; when there is plenty
of ATP, respiration slows down
• Control of catabolism is based mainly on
regulating the activity of enzymes at
strategic points in the catabolic pathway
© 2011 Pearson Education, Inc.
Figure 9.20
Glucose
AMP
Glycolysis
Fructose 6-phosphate

Stimulates

Phosphofructokinase

Fructose 1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Figure 9.UN06
Inputs
Outputs
Glycolysis
Glucose
2 Pyruvate  2
ATP
 2 NADH
Figure 9.UN07
Outputs
Inputs
2 Pyruvate
2 Acetyl CoA
2 Oxaloacetate
Citric
acid
cycle
2
ATP
8 NADH
6
CO2
2 FADH2
Figure 9.UN08
H
INTERMEMBRANE
SPACE
H
H
Cyt c
Protein complex
of electron
carriers
IV
Q
III
I
II
FADH2 FAD
NAD
NADH
(carrying electrons from food)
2 H + 1/2 O2
MITOCHONDRIAL MATRIX
H2O
Figure 9.UN09
INTERMEMBRANE
SPACE
H
ATP
synthase
MITOCHONDRIAL
MATRIX
ADP + P i
H
ATP