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Chapter 9
Cellular Respiration:
Harvesting Chemical Energy
PowerPoint® Lecture Presentations for
Lectures prepared by
Dr. Jorge L. Alonso
Florida International
University
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Photosynthesis
and
Respiration
Theme 4:
Organisms
interact with their
environments,
exchanging
matter and energy
Sunlight
Ecosystem
Photosynthesis
Cycling
of
chemical
nutrients
Heat
Chemical energy
Concept 9.1:
Catabolic
pathways yield
energy by oxidizing
organic fuels
Respiration
Heat
Photosynthesis
and
Respiration
Light
energy
ECOSYSTEM
Photosynthesis
Photosynthesis
in chloroplasts
CO2 + H2O
C6H12O6 + O2
Cellular respiration
in mitochondria
Respiration
ATP
ATP powers most cellular work
Heat
energy
Catabolic Pathways and Production of ATP
• Fermentation is a
partial degradation of
sugars that occurs
without O2 (anaerobic)
to produce a little
energy (ATP) and
ethanol (or lactate).
• Aerobic Respiration is
a more complete
degradation of sugars
that occurs with O2 and
yields much more
energy (ATP) and CO2.
Fermentation is a partial degradation of sugars that occurs without O2
(anaerobic) to produce a little energy (ATP) and ethanol (or lactate).
Alcoholic
Fermentation:
in Yeast cells,
enzymes
facilitate
production of
ethanol.
Lactic Acid
Fermentation:
in animal cells,
in the absence
of sufficient
oxygen,
enzymes
facilitate
production of
lactic acid
Other types of Fermentation
Cellular Respiration
• Cellular respiration includes both aerobic and
anaerobic respiration but is often used to refer to
aerobic respiration
• 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 (36
ATP + heat)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cellular Respiration
• It includes both aerobic
and anaerobic
components, but whole
process is refered to as
aerobic respiration
C6H12O6
2
2
2
• C6H12O6 + 6 O2 
6 CO2 + 6 H2O
+ Energy (ATP + heat)
• The whole process is
composed of three major
stages
1. Glycolysis
2. Citric Acid (Krebs) Cycle
3. Oxidative Phosphorylation
4
2
Oxidative
Phosphorylation
36
6
6
Redox Reactions: Oxidation and Reduction
• Chemical reactions in which electrons are transferred
between the reactants and release energy
eEnergy
Oxidation: substance loses electrons, or is oxidized
Na  Na+ + e-
Reducing agent
Reduction: substance gains electrons, or is reduced (the
amount of positive charge is reduced)
Cl + e-  Cl-
Oxidizing agent
• In redox reactions involving covalent (organic) compounds
the electrons are not transferred to produce ions, but a change occurs in the
way in which electron are shared in the covalent bonds (1) oxidation: epulled further away, (2) reduction: e- shared closer).
becomes oxidized
becomes reduced
+
+
4-
+
Carbon: has
e- closer
+
0
0
Oxygen:
has efurther away
2-
4+
Carbon: has
e- further
away
2-
+
2-
Oxygen:
has ecloser
+
How is the energy found in the bonding electrons of Glucose
harvested to make ATP during Cellular Respiration?
eHow are these electrons
Energy transferred to oxygen?
• Electrons from organic compounds are usually first transferred
to NAD+, an electron-acceptor coenzyme found in cells
• Electrons are carried in the form of high energy hydride ions:
H- or H:-
Carbohydrate
(reduced)
(oxidized)
(oxidized)
(reduced)
• Each NADH (the reduced form of NAD+) represents stored
energy that is tapped to synthesize ATP
Nicotinamide Adenine Diphosphate (NAD+  NADH)
H
H
2 e– + 2 H+
Carbohydrate
(reduced)
2 e– + H+
NADH
H+
Dehydrogenase
Reduction of NAD+
NAD+
+
+ H+
2[H]
Oxidation of NADH
Nicotinamide
(reduced form)
Nicotinamide
(oxidized form)
•
•
•
•
How are electrons and
their energy harvested
from Glucose?
NADH and FADH2 gather
electrons (H-) at different
stages of respiration and
passes them to the electron
transport chain.
C6H12O6
2
2
2
The electron transport chain
passes energetic electrons to
O2 in a series of enzymatically
controlled steps (instead of
one explosive reaction)
4
(H-)
O2 pulls electrons
down
the chain in an energy-yielding
tumble and H2O is produced.
The energy yielded is used to
regenerate ATP (oxidative
phosphorylation)
2
Oxidative
Phosphorylation
36
6
6
•
The electron transport chain passes energetic electrons to O2 in a series
of enzymatically controlled steps (instead of one explosive reaction)
H2 + 1/2 O2
2H
(from glucose via NADH)
Controlled
release of
2 H+ + 2 e–
energy for
synthesis of
ATP
1/
2 O2
Explosive
release of
heat and light
energy
1/ O
2 2
(a) Uncontrolled reaction
(b) Cellular respiration
The Stages of Cellular Respiration:
1.
Glycolysis (breaks
2.
down glucose into two
molecules of pyruvate),
some ATP and NADH
produced
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
ATP
Substrate-level
phosphorylation
The Citric Acid (Krebs)
Cycle (breaks down
pyruvate into CO2),
producing some ATP,
NADH and FADH2
The Stages of Cellular Respiration:
1.
Glycolysis (breaks
2.
down glucose into two
molecules of pyruvate),
some ATP and NADH
produced
The Citric Acid (Krebs) 3.
Cycle (breaks down
pyruvate into CO2),
producing some ATP,
NADH and FADH2
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative Phosphorylation
(uses H2O to oxidize the
NADH & FADH2 produced in
previous steps, producing O2
and lots of ATP)
Mitochondrion
Cytosol
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
The Stages of Cellular Respiration:
1.
Glycolysis (breaks
2.
down glucose into two
molecules of pyruvate),
some ATP and NADH
produced
The Citric Acid (Krebs) 3.
Cycle (breaks down
pyruvate into CO2),
producing some ATP,
NADH and FADH2
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative Phosphorylation
(uses H2O to oxidize the
NADH & FADH2 produced in
previous steps, producing O2
and lots of ATP)
Oxidative
phosphorylation:
(1) Electron
transport and
(2) chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
• About 10% of ATP is formed in glycolysis
and the citric acid cycle by substrate-level
phosphorylation
Enzyme
Substrate-Phosphorylated + ADP
Enzyme
 Product-unPhosphorylated + ATP
Enzyme
ADP
P
Substrate
+
Product
ATP
The process that generates most of the ATP is
called oxidative phosphorylation because it
BioFlix: Cellular Respiration
is powered by redox reactions
H+
H+
H+
H+
Protein complex
of electron
carriers
Cyt c
V
Q


ATP
synthase

FADH2
NADH
2 H+ + 1/2O2
NAD+
ADP + P i
(carrying electrons
from food)
ATP
H+
1 Electron transport chain
•
H2O
FAD
2 Chemiosmosis
This process accounts for almost 90% of the ATP generated by respiration
Concept 9.2: Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate
•
Glycolysis
(“splitting of sugar”)
breaks down
glucose into two
molecules of
pyruvate
+
Glucose
•
2 Pyruvates
Glycolysis has two
major phases:
(1)Energy investment
phase
(2)Energy payoff
phase
Glucose
ATP
1
Hexokinase
ADP
Glucose
Glucose-6-phosphate
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
Glucose
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose-6-phosphate
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose-6-phosphate
Glucose
ATP
1
Hexokinase
ADP
Fructose-6-phosphate
Glucose-6-phosphate
2
Phosphoglucoisomerase
ATP
3
Phosphofructokinase
Fructose-6-phosphate
ATP
3
Phosphofructokinase
ADP
ADP
Fructose1, 6-bisphosphate
Fructose1, 6-bisphosphate
Glucose
ATP
1
Hexokinase
ADP
Glucose-6-phosphate
2
Phosphoglucoisomerase
Fructose1, 6-bisphosphate
4
Fructose-6-phosphate
ATP
Aldolase
3
Phosphofructokinase
ADP
5
Isomerase
Fructose1, 6-bisphosphate
4
Aldolase
5
Isomerase
Dihydroxyacetone
phosphate
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Glyceraldehyde3-phosphate
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
Glyceraldehyde3-phosphate
2 NAD+
2 NADH
6
Triose phosphate
dehydrogenase
2 Pi
+ 2 H+
2 1, 3-Bisphosphoglycerate
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
2 1, 3-Bisphosphoglycerate
2 ADP
2
3-Phosphoglycerate
2 ATP
2
7
Phosphoglycerokinase
3-Phosphoglycerate
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
3-Phosphoglycerate
8
2
3-Phosphoglycerate
Phosphoglyceromutase
2
8
Phosphoglyceromutase
2-Phosphoglycerate
2
2-Phosphoglycerate
2 NAD+
2 NADH
+ 2 H+
6
Triose phosphate
dehydrogenase
2 Pi
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
3-Phosphoglycerate
2
2-Phosphoglycerate
8
Phosphoglyceromutase
9
2
2 H2O
2-Phosphoglycerate
Enolase
9
Enolase
2 H2O
2
Phosphoenolpyruvate
2
Phosphoenolpyruvate
2 NAD+
6
Triose phosphate
dehydrogenase
2 Pi
2 NADH
+ 2 H+
2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase
2 ATP
2
Phosphoenolpyruvate
2 ADP
2
3-Phosphoglycerate
8
Phosphoglyceromutase
2 ATP
2
10
Pyruvate
kinase
2-Phosphoglycerate
9
2 H2O
Enolase
2 Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
2
Pyruvate
Pyruvate
Concept 9.3: The Citric
Acid (Krebs) Cycle
completes the energyyielding oxidation of
organic molecules
C6H12O6
2
2
2
• In the presence of O2,
pyruvate enters the
mitochondrion
• Before the citric acid
cycle can begin,
pyruvate must be
converted to acetyl CoA,
which links the cycle to
glycolysis
4
2
Oxidative
Phosphorylation
36
6
6
The junction between glycolysis & the citric acid cycle:
Conversion of pyruvate to acetyl CoA
•
In the presence of O2, pyruvate enters the mitochondrion, at the cost of an
ATP for transport of each pyruvate molecule
•
Before the citric acid cycle can begin, pyruvate must be converted to acetyl
CoA, which links the cycle to glycolysis
CYTOSOL
MITOCHONDRION
NAD+
NADH + H+
2
1
Pyruvate
Transport protein
3
CO2
Coenzyme A
Acetyl CoA
The junction between glycolysis & the citric acid cycle:
Conversion of pyruvate to acetyl CoA
Enzymes of Glycolysis juction to CAC:
1.
Citrate synthase
2.
Pyruvate carboxylase
The Citric Acid
(Krebs) Cycle
Pyruvate
CO2
NAD+
CoA
• The CAC takes
place within the
mitochondrial matrix
NADH
+ H+
Acetyl CoA
CoA
CoA
• The cycle oxidizes
organic fuel derived
from pyruvate,
generating 1 ATP, 3
NADH, and 1
FADH2 per turn
Citric
acid
cycle
FADH2
2 CO2
3 NAD+
3 NADH
FAD
+ 3 H+
ADP + P i
ATP
The Citric Acid
(Krebs) Cycle
•
In the first of eight steps in
the CAC, the acetyl group of
acetyl CoA joins the cycle by
combining with oxaloacetate,
forming citrate. Each step is
catalyzed by a specific
enzyme
Enzymes of CAC:
1.
•
Citrate synthase
The next seven steps
decompose the citrate back
to oxaloacetate, making the
process a cycle
Acetyl CoA
CoA—SH
1
Oxaloacetate
Citrate
Citric
Acid
Cycle
The Citric Acid
(Krebs) Cycle
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Enzymes of CAC:
1.
Citrate synthase
2.
Aconitase
Citric
Acid
Cycle
The Citric Acid
(Krebs) Cycle
•
Acetyl CoA
CoA—SH
1
The NADH and FADH2
produced by the cycle relay
electrons extracted from
food to the electron transport
chain
Enzymes of CAC:
1.
Citrate synthase
2.
Aconitase
3.
Isocirate dehydrogenase
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
Acid
Cycle
3
NADH
+ H+
CO2
-Ketoglutarate
The Citric Acid
(Krebs) Cycle
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Enzymes of CAC:
Citric
Acid
Cycle
NADH
+ H+
3
CO2
CoA—SH
1.
Citrate synthase
2.
Aconitase
3.
Isocirate dehydrogenase
4.
-Ketoglutarate
4
NAD+
ά-ketoglutarate dehydrogenase
Succinyl
CoA
NADH
+ H+
CO2
The Citric Acid
(Krebs) Cycle
Acetyl CoA
CoA—SH
1
H2O
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
Acid
Cycle
Enzymes of CAC:
NADH
+ H+
3
CO2
CoA—SH
1.
Citrate synthase
2.
Aconitase
3.
Isocirate dehydrogenase
4.
ά-ketoglutarate dehydrogenase
5.
Succinyl-CoA synthetase
-Ketoglutarate
4
CoA—SH
5
NAD+
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
The Citric Acid
(Krebs) Cycle
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
Acid
Cycle
Enzymes of CAC:
1.
Citrate synthase
2.
Aconitase
3.
Isocirate dehydrogenase
4.
ά-ketoglutarate dehydrogenase
5.
Succinyl-CoA synthetase
6.
Succinate dehydrogenase
Fumarate
NADH
+ H+
3
CO2
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
The Citric Acid
(Krebs) Cycle
Acetyl CoA
CoA—SH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
Acid
Cycle
7
H2O
Enzymes of CAC:
1.
Citrate synthase
2.
Aconitase
3.
Isocirate dehydrogenase
4.
ά-ketoglutarate dehydrogenase
5.
Succinyl-CoA synthetase
6.
Succinate dehydrogenase
7.
Fumarase
Fumarate
NADH
+ H+
3
CO2
CoA—SH
-Ketoglutarate
4
6
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
The Citric Acid
(Krebs) Cycle
Acetyl CoA
CoA—SH
NADH
+H+
H2O
1
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
Acid
Cycle
7
H2O
Enzymes of CAC:
1.
Citrate synthase
2.
Aconitase
3.
Isocirate dehydrogenase
4.
ά-ketoglutarate dehydrogenase
5.
Succinyl-CoA synthetase
6.
Succinate dehydrogenase
7.
Fumarase
8.
Malate dehydrogenase
Fumarate
NADH
+ H+
3
CO2
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
PowerPoint® Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Concept 9.4: During
oxidative
phosphorylation,
chemiosmosis couples
electron transport to
ATP synthesis
C6H12O6
2
2
2
•
•
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
4
2
Oxidative
Phosphorylation
36
6
6
Oxidative Phosphorylation
•
The Enzymes for Oxidative Phosphorylation are located in the inner membrane of the cristae in
the mitochondrion.
•
Most of the chain’s components are proteins, which exist in multiprotein complexes
•
Oxidative Phosphorylation is composed of two separate processes:
1.
Electron Transport Chain, which uses the energy in electrons to pump H+ ions from the
matrix to the intermembrane space. {ETC 1}
2.
Chemosmosis, which uses the osmotic pressure from now concentrated H+ ions to
energize ATP {ChmOsmo}
INTER-
Glycolysis
MEMBRANE
SPACE
Krebs
Cycle
MITOCHONDIRAL
MATRIX
The Pathway of
Electron Transport
NADH
•
Electrons are transferred from NADH
or FADH2 to the electron transport
chain
50
2 e–
Electrons are passed through a
number of proteins including
cytochromes (each with an iron
atom) to O2

FMN
FAD
Multiprotein
complexes
FAD
Fe•S 
Fe•S
Q

Cyt b
30
Fe•S
Cyt c1
IV
Cyt c
Cyt a
•
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
•
FADH2
2 e–
40
•
NAD+
The electron transport chain
generates no ATP
Cyt a3
20
10
2 e–
(from NADH
or FADH2)
0
2 H+ + 1/2 O2
H 2O
The Pathway of Electron Transport
• 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
channels in 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
INTERMEMBRANE
SPACE
MITOCHONDIRAL
MATRIX
ATP synthase, a molecular mill
INTERMEMBRANE SPACE
• The energy stored in a H+
gradient across a
membrane couples the
redox reactions of the
electron transport chain to
ATP synthesis
• The
gradient is referred
to as a proton-motive
force, emphasizing its
capacity to do work
H+
H+
Stator
Rotor
Internal
rod
Catalytic
knob
ADP
+
P
i
ATP
MITOCHONDRIAL MATRIX
Fig. 9-15
EXPERIMENT
Magnetic bead
Electromagnet
Sample
Internal
rod
Catalytic
knob
Nickel
plate
RESULTS
Rotation in one direction
Number of photons
detected (103)
Rotation in opposite direction
No rotation
30
25
20
0
Sequential trials
Fig. 9-15a
EXPERIMENT
Magnetic bead
Electromagnet
Sample
Internal
rod
Catalytic
knob
Nickel
plate
Fig. 9-15b
RESULTS
Rotation in one direction
Rotation in opposite direction
No rotation
30
25
20
0
Sequential trials
Fig. 9-16
H+
H+
H+
H+
Protein complex
of electron
carriers
Cyt c
V
Q


ATP
synthase

FADH2
NADH
2 H+ + 1/2O2
H2O
FAD
NAD+
ADP + P i
(carrying electrons
from food)
ATP
H+
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis
ATP Production by Cellular Respiration
•
During cellular respiration, most energy flows in this sequence:
glucose  NADH  electron transport chain  proton-motive force  ATP
•
About 40% of the energy in a glucose molecule is transferred to ATP during
cellular respiration, making about 38 ATP
Concept 9.5:
Fermentation and
anaerobic respiration
enable cells to
produce ATP without
the use of oxygen
C6H12O6
2
2
2
•
Most cellular respiration
requires O2 to produce ATP
•
Glycolysis can produce ATP
with or without O2 (in aerobic
or anaerobic conditions)
•
In the absence of O2,
glycolysis couples with
fermentation or anaerobic
respiration to produce ATP
4
2
Oxidative
Phosphorylation
36
6
6
•
Anaerobic respiration uses an
electron transport chain with an
electron acceptor other than O2,
for example sulfate
•
Fermentation uses
phosphorylation instead of an
electron transport chain to
generate ATP
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Types of Fermentation
Animation: Fermentation Overview
2 ADP + 2 Pi
•
Fermentation consists of glycolysis plus
reactions that regenerate NAD+, which can be
reused by glycolysis
Glucose
Two common types are alcohol fermentation and
lactic acid fermentation
•
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
• 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
Glycolysis
2 Pyruvate
•
•
2 ATP
2 NAD+
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 Pi
Glucose
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
C6H12O6
Fermentation and
Aerobic Respiration
Compared
•
•
•
Both processes use
glycolysis to oxidize glucose
and other organic fuels to
pyruvate
2
2
2
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
38 ATP per glucose
molecule; fermentation
produces 2 ATP per glucose
molecule
4
2
Oxidative
Phosphorylation
36
6
6
• 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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Fig. 9-19
Glucose
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
The Evolutionary Significance of Glycolysis
• Glycolysis occurs in nearly all organisms
• Glycolysis probably evolved in ancient
prokaryotes before there was oxygen in the
atmosphere
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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
• Although carbohydrates, fats, and proteins
are all consumed as fuel, it is helpful to trace
cellular respiration with the sugar glucose:
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The Versatility of Catabolism
•
•
•
•
Catabolic pathways funnel electrons
from many kinds of organic molecules
into cellular respiration
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
Carbohydrates
Amino
acids
Sugars
Glycolysis
Glycolysis accepts a wide range of
carbohydrates
Proteins must be digested to amino
acids; amino groups can feed
glycolysis or the citric acid cycle
Proteins
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
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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
Glucose
AMP
Glycolysis
Fructose-6-phosphate
–
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Fig. 9-UN5
Outputs
Inputs
2
ATP
Glycolysis
+
2 NADH
Glucose
2
Pyruvate
Fig. 9-UN6
Inputs
Outputs
S—CoA
C
2
ATP
6
NADH
O
CH3
2
Acetyl CoA
O
C
COO
CH2
COO
2
Oxaloacetate
Citric acid
cycle
2 FADH2
Fig. 9-UN7
INTERMEMBRANE
SPACE
H+
ATP
synthase
ADP + P i
MITOCHONDRIAL
MATRIX
ATP
H+
Fig. 9-UN8
Time
Fig. 9-UN9
You should now be able to:
1. Explain in general terms how redox reactions
are involved in energy exchanges
2. Name the three stages of cellular respiration;
for each, state the region of the eukaryotic
cell where it occurs and the products that
result
3. In general terms, explain the role of the
electron transport chain in cellular respiration
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
4. Explain where and how the respiratory
electron transport chain creates a proton
gradient
5. Distinguish between fermentation and
anaerobic respiration
6. Distinguish between obligate and facultative
anaerobes
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings