09_Lecture_Presentation.ppt

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Chapter 9
Cellular Respiration:
Harvesting Chemical Energy

Overview: Life Is Work
• Living cells require energy from outside
sources
• Some animals, such as the giant panda, obtain
energy by eating plants, and some animals
feed on other organisms that eat plants

• 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

Fig. 9-2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
Organic
molecules
+ O2
ATP powers most cellular work
Heat
energy
ATP

Concept 9.1: Catabolic pathways yield energy by
oxidizing organic fuels
• Several processes are central to cellular
respiration and related pathways

Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is
exergonic
• Fermentation is a partial degradation of
sugars that occurs without O2
• Aerobic respiration consumes organic
molecules and O2 and yields ATP
• Anaerobic respiration is similar to aerobic
respiration but consumes compounds other
than O2

• 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
(ATP + heat)

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

The Principle of Redox
• 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)

Fig. 9-UN1
becomes oxidized
(loses electron)
becomes reduced
(gains electron)

Fig. 9-UN2
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

Fig. 9-3
Reactants
becomes oxidized
becomes reduced
Products
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide Water

Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration, the fuel (such as
glucose) is oxidized, and O2 is reduced:

Fig. 9-UN3
becomes oxidized
becomes reduced

Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
• In cellular respiration, glucose and other
organic molecules are broken down in a series
of steps
• 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

Fig. 9-4
Dehydrogenase
Reduction of NAD+
Oxidation of NADH
2 e– + 2 H+
2 e– + H+
NAD+
+ 2[H]
NADH
+
H+
H+
Nicotinamide
(oxidized form)
Nicotinamide
(reduced form)

• 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 energy-
yielding tumble
• The energy yielded is used to regenerate ATP

Fig. 9-5
(a) Uncontrolled reaction
H2 + 1/2 O2
Explosive
release of
heat and light
energy
(b) Cellular respiration
Controlled
release of
energy for
synthesis of
ATP
2 H+ + 2 e–
2 H 1/2 O2
(from food via NADH)
1/2 O2

The Stages of Cellular Respiration: A Preview
• Cellular respiration 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)

Fig. 9-6-1
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH

Fig. 9-6-2
Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Substrate-level
phosphorylation
ATP
Electrons carried
via NADH and
FADH2
Citric
acid
cycle

Fig. 9-6-3
Mitochondrion
Substrate-level
phosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carried
via NADH
Substrate-level
phosphorylation
ATP
Electrons carried
via NADH and
FADH2
Oxidative
phosphorylation
ATP
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis

• The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
BioFlix: Cellular Respiration

• 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

Fig. 9-7
Enzyme
ADP
P
Substrate
Enzyme
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

Fig. 9-8
Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
formed
4 ATP
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+
2 NADH + 2 H+
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2O
Glucose
Net
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

Fig. 9-9-1
ATP
ADP
Hexokinase
1
ATP
ADP
Hexokinase
1
Glucose
Glucose-6-phosphate
Glucose
Glucose-6-phosphate

Fig. 9-9-2
Hexokinase
ATP
ADP
1
Phosphoglucoisomerase
2
Phosphogluco-
isomerase
2
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Glucose-6-phosphate

1
Fig. 9-9-3
Hexokinase
ATP
ADP
Phosphofructokinase
ATP
ADP
2
3
ATP
ADP
Phosphofructo-
kinase
Fructose-
1, 6-bisphosphate
Glucose
Glucose-6-phosphate
Fructose-
1, 6-bisphosphate
1
2
3
3

Fig. 9-9-4
Glucose
ATP
ADP
Hexokinase
Glucose-6-phosphate
ATP
ADP
Phosphofructokinase
Fructose-
1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate
1
2
3
4
5
Aldolase
Isomerase
Fructose-
1, 6-bisphosphate
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate
4
5

Fig. 9-9-5
2 NAD+
NADH
2
+ 2 H+
2
2 Pi
Triose phosphate
dehydrogenase
1, 3-Bisphosphoglycerate
6
2 NAD+
Glyceraldehyde-
3-phosphate
Triose phosphate
dehydrogenase
NADH
2
+ 2 H+
2 P i
6
2
2

Fig. 9-9-6
2 NAD+
NADH
2
Triose phosphate
dehydrogenase
+ 2 H+
2 P i
2
2 ADP
Phosphoglycerokinase
2 ATP
2 3-Phosphoglycerate
6
7
2
2 ADP
2 ATP
3-Phosphoglycerate
Phosphoglycero-
kinase
2
7

Fig. 9-9-7
3-Phosphoglycerate
Triose phosphate
dehydrogenase
2 NAD+
2 NADH
+ 2 H+
2 P i
2
2 ADP
2 ATP
3-Phosphoglycerate
2
Phosphoglyceromutase
2-Phosphoglycerate
2
2-Phosphoglycerate
2
2
Phosphoglycero-
mutase
6
7
8
8

Fig. 9-9-8
2 NAD+
NADH
2
2
2
2
2
+ 2 H+
Triose phosphate
dehydrogenase
2 P i
2 ADP
2 ATP
3-Phosphoglycerate
Enolase
2-Phosphoglycerate
2 H2O
Phosphoenolpyruvate
9
8
7
6
2 2-Phosphoglycerate
Enolase
2
2 H2O
Phosphoenolpyruvate
9

Fig. 9-9-9
Triose phosphate
dehydrogenase
2 NAD+
NADH
2
2
2
2
2
2
2 ADP
2 ATP
Pyruvate
Pyruvate kinase
Phosphoenolpyruvate
Enolase
2 H2O
2-Phosphoglycerate
3-Phosphoglycerate
2 ATP
2 ADP
+ 2 H+
6
7
8
9
10
2
2 ADP
2 ATP
Phosphoenolpyruvate
Pyruvate
kinase
2 Pyruvate
10
2 P i

Concept 9.3: The citric acid cycle completes the
energy-yielding oxidation of organic molecules
• 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

Fig. 9-10
CYTOSOL MITOCHONDRION
NAD+ NADH + H+
2
1 3
Pyruvate
Transport protein
CO2
Coenzyme A
Acetyl CoA

• The citric acid cycle, also called the Krebs
cycle, takes place within the mitochondrial
matrix
• The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1
FADH2 per turn

Fig. 9-11
Pyruvate
NAD+
NADH
+ H+
Acetyl CoA
CO2
CoA
CoA
CoA
Citric
acid
cycle
FADH2
FAD
CO2
2
3
3 NAD+
+ 3 H+
ADP + P i
ATP
NADH

• 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

Fig. 9-12-1
Acetyl CoA
Oxaloacetate
CoA—SH
1
Citrate
Citric
acid
cycle

Fig. 9-12-2
Acetyl CoA
Oxaloacetate
Citrate
CoA—SH
Citric
acid
cycle
1
2
H2O
Isocitrate

Fig. 9-12-3
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
Citric
acid
cycle
Isocitrate
1
2
3
NAD+
NADH
+ H+
-Keto-
glutarate
CO2

Fig. 9-12-4
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
Isocitrate
NAD+
NADH
+ H+
Citric
acid
cycle
-Keto-
glutarate
CoA—SH
1
2
3
4
NAD+
NADH
+ H+
Succinyl
CoA
CO2
CO2

Fig. 9-12-5
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
Isocitrate
NAD+
NADH
+ H+
CO2
Citric
acid
cycle
CoA—SH
-Keto-
glutarate
CO2
NAD+
NADH
+ H+
Succinyl
CoA
1
2
3
4
5
CoA—SH
GTP GDP
ADP
Pi
Succinate
ATP

Fig. 9-12-6
Acetyl CoA
CoA—SH
Oxaloacetate
H2O
Citrate
Isocitrate
NAD+
NADH
+ H+
CO2
Citric
acid
cycle
CoA—SH
-Keto-
glutarate
CO2
NAD+
NADH
+ H+
CoA—SH
P
Succinyl
CoA
i
GTP GDP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
1
2
3
4
5
6

Fig. 9-12-7
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
Isocitrate
NAD+
NADH
+ H+
CO2
-Keto-
glutarate
CoA—SH
NAD+
NADH
Succinyl
CoA
CoA—SH
P
P
GDP
GTP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
Citric
acid
cycle
H2O
Malate
1
2
5
6
7
i
CO2
+ H+
3
4

Fig. 9-12-8
Acetyl CoA
CoA—SH
Citrate
H2O
Isocitrate
NAD+
NADH
+ H+
CO2
-Keto-
glutarate
CoA—SH
CO2
NAD+
NADH
+ H+
Succinyl
CoA
CoA—SH
P i
GTP GDP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
Citric
acid
cycle
H2O
Malate
Oxaloacetate
NADH
+H+
NAD+
1
2
3
4
5
6
7
8

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

The Pathway of Electron Transport
• The electron transport chain is in the 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

Fig. 9-13
NADH
NAD+
2
FADH2
2 FAD
Multiprotein
complexes
FAD
Fe•S
FMN
Fe•S
Q
Fe•S

Cyt b


Cyt c1
Cyt c
Cyt a
Cyt a3
I
V
50
40
30
20
10 2
(from NADH
or FADH2)
0 2 H+ + 1/2 O2
H2O
e–
e–
e–

• 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
• The chain’s function is to break the large free-
energy drop from food to O2 into smaller steps
that release energy in manageable amounts

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 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

Fig. 9-14
INTERMEMBRANE SPACE
Rotor
H+
Stator
Internal
rod
Cata-
lytic
knob
ADP
+
P ATP
i
MITOCHONDRIAL MATRIX

Fig. 9-15
EXPERIMENT
Electromagnet
RESULTS
Sample
Magnetic bead
Internal
rod
Catalytic
knob
Nickel
plate
Rotation in one direction
Rotation in opposite direction
No rotation
Sequential trials
Number
of
photons
detected
(10
3
)
0
20
25
30

Fig. 9-15a
EXPERIMENT
Sample
Magnetic bead
Internal
rod
Catalytic
knob
Nickel
plate
Electromagnet

Fig. 9-15b
Rotation in one direction
Rotation in opposite direction
No rotation
Sequential trials
30
25
20
0
RESULTS

• 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 proton-
motive force, emphasizing its capacity to do
work

Fig. 9-16
Protein complex
of electron
carriers
H+
H+
H+
Cyt c
Q



V
FADH2 FAD
NAD+
NADH
(carrying electrons
from food)
Electron transport chain
2 H+ + 1/2O2 H2O
ADP + P i
Chemiosmosis
Oxidative phosphorylation
H+
H+
ATP
synthase
ATP
2
1

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 40% of the energy in a glucose molecule
is transferred to ATP during cellular respiration,
making about 38 ATP

Fig. 9-17
Maximum per glucose: About
36 or 38 ATP
+ 2 ATP
+ 2 ATP + about 32 or 34 ATP
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Citric
acid
cycle
2
Acetyl
CoA
Glycolysis
Glucose
2
Pyruvate
2 NADH 2 NADH 6 NADH 2 FADH2
2 FADH2
2 NADH
CYTOSOL Electron shuttles
span membrane
or
MITOCHONDRION

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
• 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

• 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

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

• 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
Animation: Fermentation Overview

Fig. 9-18
2 ADP + 2 Pi 2 ATP
Glucose Glycolysis
2 NAD+ 2 NADH
2 Pyruvate
+ 2 H+
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 Pi 2 ATP
Glucose Glycolysis
2 NAD+ 2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
2 CO2

Fig. 9-18a
2 ADP + 2 P i 2 ATP
Glucose Glycolysis
2 Pyruvate
2 NADH
2 NAD+
+ 2 H+
CO2
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2

• 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

Fig. 9-18b
Glucose
2 ADP + 2 P i 2 ATP
Glycolysis
2 NAD+ 2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation

Fermentation and Aerobic Respiration Compared
• Both processes use glycolysis to oxidize
glucose and other organic fuels to pyruvate
• 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

• 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

Fig. 9-19
Glucose
Glycolysis
Pyruvate
CYTOSOL
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Acetyl CoA
Ethanol
or
lactate
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

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

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

• 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

Fig. 9-20
Proteins Carbohydrates
Amino
acids
Sugars
Fats
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3-
Pyruvate
P
NH3
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation

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

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

Fig. 9-21
Glucose
Glycolysis
Phosphofructokinase
Fructose-1,6-bisphosphate
Inhibits
AMP
Stimulates
Inhibits
Pyruvate
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
ATP
+
–
–

Fig. 9-UN5
Inputs
Glycolysis
Outputs
+
2
2
ATP
NADH
2
Glucose Pyruvate

Fig. 9-UN6
Inputs Outputs
Acetyl CoA
2
2
2
2
6
ATP
NADH
FADH2
Oxaloacetate
Citric acid
cycle
S—CoA
CH3
C O
O C COO
CH2
COO

Fig. 9-UN7
INTER-
MEMBRANE
SPACE
H+
ATP
synthase
ATP
ADP + P i
H+
MITO-
CHONDRIAL
MATRIX

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

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

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