PRESENTATIONS
For 2/7/12
LECTURE CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 9
Overview: Life Is Work
Living cells require energy from outside
sources
Cellular Respiration and
Fermentation
Lectures by
Erin Barley
Kathleen Fitzpatrick
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Energy flow through living systems
In most ecosystems,
energy enters as
sunlight and leaves as
heat
Cells must regenerate
ATP from ADP + Pi
Concept 9.1: Catabolic pathways yield
energy by oxidizing organic fuels
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
The breakdown of organic molecules is
exergonic
Which provides energy to regenerate ATP
ATP
powers most cellular work
Figure 9.2
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Heat
energy
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Redox Reactions: Oxidation and Reduction
Catabolic Pathways and Production of ATP
Fermentation
is a partial degradation of sugars that occurs
without O2
We will get back to this later
Catabolic pathways yield energy
Due to the transfer of electrons from food molecules to
more electronegative atoms (usually oxygen)
The electrons lose energy and become more stable
when transferred to oxygen
Yields a limited amount of ATP
Cellular respiration
Consumes organic molecules and O2
Yields ATP (and CO2 and H2O as waste)
We wont talk about anaerobic respirations
Cellular respiration in this class will mean aerobic
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Redox example
Redox Reactions: Oxidation and Reduction
Example of a redox reaction with complete transfer of
an electron
Redox reactions
Transfer electrons, either fully or partially
In oxidation
A substance loses electrons, and is
oxidized
becomes oxidized
(loses electron)
Na + Cl
Na+ + Cl
becomes reduced
In reduction
(gains electron)
A substance gains electrons, and is
reduced
(gaining electrons will reduce charge)
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Many redox reactions only change the degree of electron
sharing in covalent bonds
Products
Reactants
Oxidation of Organic Fuel Molecules During
Cellular Respiration
During cellular respiration
becomes oxidized
Energy
Glucose is oxidized to CO2 and oxygen is reduced to H2O
Electrons "fall" toward oxygen with a -G
becomes reduced
becomes oxidized
C6H12O6 + 6O2
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water
Figure 9.3
Stepwise Energy Harvest via
Electron Transport Chain
becomes reduced
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NAD+
and the
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
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6CO2 + 6H2O + Energy
Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
Cellular respiration
Glucose is oxidized in a series of chemical
reactions to efficiently collect energy
that can be used to make ATP
from ADP + Pi
Electrons are transferred to oxygen
via "shuttle" molecules and an electron
transport chain (ETC)
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NADH shuttles electrons
Electrons from organic compounds
NADH, the reduced form of NAD+
Are usually first transferred to NAD+, a coenzyme, to
produce NADH
Passes electrons from food to the electron transport
chain
The electron transport chain (ETC)
Passes electrons to oxygen in a series of steps instead
of in one explosive reaction, discussed later.
Figure 9.4
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Figure 9.5
H2 + 1/2 O2
2H
1/
2
+
Free energy, G
port
Free energy, G
s
tran
tron ain
ch
Explosive
release of
heat and light
energy
Elec
(from food via NADH)
Controlled
release of
2 H+ + 2 eenergy for
synthesis of
ATP
ATP
ATP
ATP
2 e1/
2
2 H+
H 2O
(a) Uncontrolled reaction
If electron transfer is rapid
and uncontrolled
O2
H 2O
(b) Cellular respiration
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
Electron transport chain
Chemiosmosis
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Figure 9.6-3
Substrate-level phosphorylation
Both glycolysis and the citric acid cycle
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Generate some ATP by substrate-level phosphorylation
The ATP is made directly
Glycolysis
Glucose
Pyruvate
CYTOSOL
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Enzyme
Enzyme
MITOCHONDRION
ADP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
ATP
ATP
Substrate
P
Oxidative
phosphorylation
Figure 9.7
+
ATP
Product
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The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
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
BioFlix: Cellular Respiration
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Glycolysis
Concept 9.2: Glycolysis harvests energy by oxidizing
glucose to pyruvate
Glycolysis consists of
two major phases
Means splitting of sugar
Oxidative
phosphorylation
Energy payoff phase
ATP
Energy investment phase
Glucose
This figure contains the
information you should know
for exams
Breaks down 1 glucose (6C) into 2 pyruvate (3C)
molecules
Citric
acid
cycle
ATP
ATP
Energy investment phase
Glycolysis
Glycolysis
2
2 ATP
used
4
4 ATP
formed
2 NADH
+ 2 H+
2 ADP + 2 P
Energy payoff phase
Occurs in the cytosol of the cell
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H +
2 Pyruvate + 2 H2O
Glucose
2 Pyruvate + 2 H2O
+ 4 ATP 2 ATP
Figure 9.8
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2 ATP + 2 H+
2 NADH
2 NAD+ + 4 e + 4 H +
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Figure 9.9-4
Figure 9.9-9
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ATP
Hexokinase
1
Fructose 1,6-bisphosphate
Glycolysis: Energy Payoff Phase
ADP
ADP
Phosphoglucoisomerase
3
2 NADH
Phosphofructokinase
2
2 ATP
2 NAD+
Aldolase
Dihydroxyacetone
phosphate
Triose
phosphate
dehydrogenase
6
5
2 ADP
2 H2O
2
2
2 ATP
2 ADP
2
4
Glyceraldehyde
3-phosphate
Isomerase
+ 2 H+
1,3-Bisphosphoglycerate
7
Enolase
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
3-Phosphoglycerate
8
2-Phosphoglycerate
9
Pyruvate
kinase
Phosphoenolpyruvate (PEP)
10
Pyruvate
To
step 6
2 Pyruvate
(3C each)
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Concept 9.3: After pyruvate is oxidized, the
citric acid cycle completes the energyyielding oxidation of organic molecules
Oxidation of to Pyruvate Acetyl CoA
Before the citric acid cycle can begin
each pyruvate is converted to acetyl Coenzyme A
(acetyl CoA)
As it enters the mitochondrion
a multienzyme complex catalyzes three reactions
In the presence of O2, pyruvate enters the
mitochondrion (in eukaryotic cells) where the
oxidation of glucose is completed
The citric acid cycle
Takes place in the matrix of the mitochondrion
Does NOT use oxygen directly, but only can
function if oxygen is available
for the next step, oxidative phosphorylation
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Figure 9.11
The Citric Acid Cycle (Krebs cycle)
Completes the break down of pyruvate to CO2
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
Pyruvate
(from glycolysis,
2 molecules per glucose)
An overview of the
citric acid cycle
(for exams, know this info,
plus citrate and OAA)
note that CO2 is a waste
product
The cycle oxidizes organic fuel derived from pyruvate,
generating 1 ATP, 3 NADH, and 1 FADH2 per turn
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Figure 9.12-8
Concept 9.4: During oxidative
phosphorylation, chemiosmosis couples
electron transport to ATP synthesis
Acetyl CoA
CoA-SH
NADH
H 2O
1
+ H+
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
H 2O
Citric
acid
cycle
7
Fumarate
NADH
3
+ H+
CO2
CoA-SH
-Ketoglutarate
6
4
CoA-SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
Pi
Succinyl
CoA
CO2
NADH
+ H+
NADH and FADH2
From glycolysis and the citric acid cycle
Donate electrons to the electron transport
chain (ETC)
The ETC powers a proton pump, that in
turn powers ATP synthesis
ADP
ATP
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The Pathway of Electron Transport
The electron transport chain is in the inner
membrane (cristae) of the mitochondrion
The Pathway of Electron Transport
Most components are proteins
exist in multiprotein complexes
Carriers alternate reduced
and oxidized states
as they accept and donate
electrons
Protons are pumped across
the membrane
From matrix to intermembrane
space
Electrons drop in free energy
as they go down the chain
finally passed to O2, forming H2O
Water is a waste product
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Proton Motive Force
Chemiosmosis: The Energy-Coupling
Mechanism
The resulting H+ gradient
Is an electrochemical gradient
Is an energycoupling
mechanism
Is referred to as the proton-motive force
Stores energy
uses energy
stored as a H+
gradient across a
membrane to drive
cellular work
Drives ATP synthesis by a process called
chemiosmosis
ATP synthase
Is the enzyme that
makes ATP in
mitochondria
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Questions?
Substrates?
Intermembrane
space
Inner
Mitochondrial
membrane
ATP
ATP
Mitochondrial
matrix
H+
H+
Protein
complex
of electron
carriers
H+
H+
Cyt c
Q
I
Inner
mitochondrial
membrane
Mechanism?
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Products?
IV
III
II
FADH2
NADH+
NAD+
(Carrying electrons
from, food)
FAD+
2 H+ + 1/2 O2
ADP +
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ATP
Pi
H+
Electron transport chain
Figure 9.15
ATP
synthase
H 2O
Chemiosmosis
Oxidative phosphorylation
An Accounting of ATP Production by
Cellular Respiration
During cellular respiration, most energy flows in
this sequence:
glucose NADH (and some FADH2) electron
transport chain proton-motive force ATP
About 34% of the energy in a glucose molecule
transferred to ATP
making about 32 ATP
The rest is in the stable waste products CO2 and
H2O and is lost as heat (first and second law of
thermodynamics)
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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
6 NADH
Pyruvate oxidation
Citric
acid
cycle
2 Acetyl CoA
+ 2 ATP
+ 2 ATP
Maximum per glucose:
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ 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
We wont talk about anaerobic respiration
Without O2
the electron transport chain will cease to operate
glycolysis couples with fermentation to produce a
little ATP in anaerobic conditions
Using substrate-level phosphorylation
CYTOSOL
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Types of Fermentation
Fermentation consists of
glycolysis plus
reactions that regenerate NAD+, which is a necessary
substrate in glycolysis
Two common types are alcohol fermentation
and lactic acid fermentation
In alcohol fermentation
Pyruvate (3C) is converted to the waste products
ethanol (2C) and CO2
Alcohol fermentation by yeast is used in brewing,
winemaking, and baking
In lactic acid fermentation
Pyruvate is reduced to was product lactate (3C) 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
Both fermentations regenerate NAD+
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Figure 9.17
Fermentation and Cellular Respiration Compared
2 ADP + 2 P i
Glucose
2 ADP + 2 P i
2 ATP
Glycolysis
Glucose
2 ATP
Glycolysis
2 Pyruvate
2 NAD +
2 NADH
+ 2 H+
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2 NAD +
2 CO2
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
Figure 9.18
The Evolutionary Significance of Glycolysis
Glycolysis
Occurs in nearly all organisms, which indicates an
early common ancestor in life
Probably evolved in ancient prokaryotes before there
was oxygen in the atmosphere
(Earth's oxygen came from photosynthetic bacteria related to
present-day cyanobacteria)
Concept 9.6: Glycolysis and the citric acid
cycle connect to many other metabolic
pathways
Catabolic pathways
Funnel electrons from many kinds of organic food
molecules into cellular respiration
carbohydrates
proteins
fats
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Figure 9.19
Proteins
Amino
acids
The Versatility of
Catabolism
Carbohydrates
Sugars
Fats
Glycerol Fatty
acids
Biosynthesis (Anabolic Pathways)
The body uses small molecules to build other
substances
These small molecules
Glycolysis
Glucose
Glyceraldehyde 3- P
N H3
Learn this figure for exams
may come directly from food
from glycolysis, or from the citric acid cycle
Pyruvate
Acetyl CoA
Many of the pathways in Figure 9.19
(previous slide) are reversible to allow the
production of
Citric
acid
cycle
carbohydrates, proteins, and fats
Oxidative
phosphorylation
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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
Control of respiration
An example of the control
of cellular respiration
Phosphofructokinase is
an allosteric enzyme
(AMP is a precursor to ADP, a
precursor to ATP)
Why would ATP and Citrate inhibit
an early step in the pathway?
Why would AMP stimulate this
same step?
at strategic points in the catabolic pathway
Figure 9.20
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