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Overview: The Energy of Life
 The living cell is a miniature chemical factory where
thousands of reactions occur
 The cell extracts energy and applies energy to
perform work
 Some organisms even convert energy to light, as in
bioluminescence
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10/15 Agenda
Metabolism Vocab
Laws of Thermodynamics
Vocab
Metabolism
Catabolism
Anabolism
Bioenergetics
Thermodynamics
System vs Surroundings
Open System vs
Closed System
Exergonic
Endergonic
Spontaneous Reaction
http://entropysimple.oxy.edu/con
tent.htm
Figure 6.1
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Concept 6.1: An organism’s metabolism
transforms matter and energy
 Metabolism is the totality of an organism’s chemical
reactions
 Metabolism is an emergent property of life that
arises from interactions between molecules within
the cell
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Metabolic Pathways
 A metabolic pathway begins with a specific
molecule and ends with a product
 Each step is catalyzed by a specific enzyme
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Figure 6.UN01
Enzyme 1
Starting
molecule
A
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Enzyme 2
C
B
Reaction 1
Enzyme 3
Reaction 2
Reaction 3
D
Product
 Catabolic pathways release energy by breaking
down complex molecules into simpler compounds
 Cellular respiration, the breakdown of glucose in the
presence of oxygen, is an example of a pathway of
catabolism
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 Anabolic pathways consume energy to build
complex molecules from simpler ones
 The synthesis of protein from amino acids is an
example of anabolism
 Bioenergetics is the study of how organisms
manage their energy resources
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Forms of Energy
 Energy is the capacity to cause change
 Energy exists in various forms, some of which can
perform work
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 Kinetic energy is energy associated with motion
 Thermal energy is kinetic energy associated with
random movement of atoms or molecules
 Heat is thermal energy in transfer from one object to
another
 Potential energy is energy that matter possesses
because of its location or structure
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 Chemical energy is potential energy available for
release in a chemical reaction
 Energy can be converted from one form to another
Animation: Energy Concepts
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Figure 6.2
A diver has more potential
energy on the platform.
Climbing up converts the kinetic
energy of muscle movement
to potential energy.
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Diving converts
potential energy to
kinetic energy.
A diver has less potential
energy in the water.
The Laws of Energy Transformation
 Thermodynamics is the study of energy
transformations
 An isolated system, such as that approximated by
liquid in a thermos, is isolated from its surroundings
 In an open system, energy and matter can be
transferred between the system and its surroundings
 Organisms are open systems
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The First Law of Thermodynamics
 According to the first law of thermodynamics, the
energy of the universe is constant
 Energy can be transferred and transformed, but it
cannot be created or destroyed
 The first law is also called the principle of
conservation of energy
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Figure 6.3
Heat
Chemical
energy
(a) First law of thermodynamics
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(b) Second law of thermodynamics
Figure 6.3a
Chemical
energy
(a) First law of thermodynamics
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Figure 6.3b
Heat
(b) Second law of thermodynamics
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The Second Law of Thermodynamics
 During every energy transfer or transformation,
some energy is unusable and is often lost as heat
 According to the second law of thermodynamics
 Every energy transfer or transformation increases the
entropy of the universe
 Entropy is a measure of disorder, or randomness
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 Living cells unavoidably convert organized forms of
energy to heat
 Spontaneous processes occur without energy
input; they can happen quickly or slowly
 For a process to occur without energy input, it must
increase the entropy of the universe
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Biological Order and Disorder
 Cells create ordered structures from less ordered
materials
 Organisms also replace ordered forms of matter and
energy with less ordered forms
 Energy flows into an ecosystem in the form of light
and exits in the form of heat
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Figure 6.4
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Figure 6.4a
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Figure 6.4b
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 The evolution of more complex organisms does not
violate the second law of thermodynamics
 Entropy (disorder) may decrease in an organism, but
the universe’s total entropy increases
 Organisms are islands of low entropy in an
increasingly random universe
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Concept 6.2: The free-energy change of a reaction
tells us whether or not the reaction occurs
spontaneously
 Biologists want to know which reactions occur
spontaneously and which require input of energy
 To do so, they need to determine energy changes
that occur in chemical reactions
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Free-Energy
Change (G)
10/20 Free Energy
10/21 Enzyme Day CH 6 notes due
10/22 review and Quiz CH6
10/23 Ch 7 – Cell Resp and Fermentation
*notes due
Today’s goals –
 Focus on free energy
 Weird concept of energy states
 Energy coupling of reactions
 ATP
In the energy diagram below, which of the energy
changes would be the same in both the enzymecatalyzed and uncatalyzed reactions?
 a
 b
 c
 d
 e
In the energy diagram below, which of the energy
changes would be the same in both the enzymecatalyzed and uncatalyzed reactions?
 a
 b
c
 d
 e
Free Energy
1.) Free Energy is the available energy to do work
2.) Chemical reactions proceed towards a more
stable state
3.) If a reaction increases amount of free energy it
is more likely to happen
4.) at Equilibrium there is the minimal amount of
free energy
5.) Free energy increases when a system is pushed
away from equilibrium
 What does this result in?
Weird fact of the day
There is not a release in energy when bonds are
broken!
Instead the new products have less free energy
than the reactants
Free Energy
1.) Free Energy is the available energy to do work
A cell does three main kinds of
work
Chemical
Transport
Mechanical
Free-Energy Change (G), Stability, and
Equilibrium
 A living system’s free energy is energy that can do
work when temperature and pressure are uniform,
as in a living cell
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∆G = Gfinal state – Ginitial state
 Only processes with a negative ∆G are spontaneous
 Spontaneous processes can be harnessed to
perform work
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Figure 6.5
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy of the
system decreases (G  0)
• The system becomes more
stable
• The released free energy can
be harnessed to do work
• Less free energy (lower G)
• More stable
• Less work capacity
(a) Gravitational
motion
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(b) Diffusion
(c) Chemical
reaction
Figure 6.5a
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy of the
system decreases (G  0)
• The system becomes more
stable
• The released free energy can
be harnessed to do work
• Less free energy (lower G)
• More stable
• Less work capacity
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Figure 6.5b
(a) Gravitational
motion
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(b) Diffusion
(c) Chemical
reaction
Figure 6.6
(a) Exergonic reaction: energy released, spontaneous
Free energy
Reactants
Amount of
energy
released
(G  0)
Energy
Products
Progress of the reaction
(b) Endergonic reaction: energy required,
nonspontaneous
Free energy
Products
Energy
Reactants
Progress of the reaction
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Amount of
energy
required
(G  0)
Figure 6.6a
(a) Exergonic reaction: energy released, spontaneous
Free energy
Reactants
Amount of
energy
released
(G  0)
Energy
Products
Progress of the reaction
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Figure 6.6b
(b) Endergonic reaction: energy required,
nonspontaneous
Free energy
Products
Energy
Reactants
Progress of the reaction
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Amount of
energy
required
(G  0)
 A catabolic pathway in a cell releases free energy in
a series of reactions
 Closed and open hydroelectric systems can serve as
analogies
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Figure 6.7
G  0
G  0
(a) An isolated hydroelectric system
(b) An open
hydroelectric
system
G  0
G  0
G  0
G  0
(c) A multistep open hydroelectric system
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Figure 6.7a
G  0
(a) An isolated hydroelectric system
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G  0
Figure 6.7b
(b) An open
hydroelectric
system
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G  0
Figure 6.7c
G  0
G  0
G  0
(c) A multistep open hydroelectric system
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Concept 6.3: ATP powers cellular work by coupling
exergonic reactions to endergonic reactions
 To do work, cells manage energy resources by
energy coupling, the use of an exergonic process
to drive an endergonic one
 Most energy coupling in cells is mediated by ATP
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Figure 6.8
Adenine
Phosphate groups
Ribose
(a) The structure of ATP
Adenosine triphosphate (ATP)
Energy
Inorganic
phosphate
Adenosine diphosphate (ADP)
(b) The hydrolysis of ATP
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Figure 6.8a
Adenine
Phosphate groups
(a) The structure of ATP
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Ribose
Figure 6.8b
Adenosine triphosphate (ATP)
Energy
Inorganic
phosphate
Adenosine diphosphate (ADP)
(b) The hydrolysis of ATP
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How the Hydrolysis of ATP Performs Work
 the energy from the exergonic reaction of ATP
hydrolysis can be used to drive an endergonic
reaction
 Overall, the coupled reactions are exergonic
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Figure 6.9
GGlu  3.4 kcal/mol
Glutamic acid Ammonia
Glutamine
(a) Glutamic acid conversion to glutamine
Phosphorylated
intermediate
Glutamic acid
Glutamine
(b) Conversion reaction coupled with ATP hydrolysis
GGlu  3.4 kcal/mol
GGlu  3.4 kcal/mol
 GATP  −7.3 kcal/mol
Net G  −3.9 kcal/mol
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GATP  −7.3 kcal/mol
(c) Free-energy change for coupled reaction
Figure 6.9a
Glutamic acid
Ammonia
Glutamine
GGlu  3.4 kcal/mol
(a) Glutamic acid conversion to glutamine
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Figure 6.9b
Glutamic acid
Phosphorylated
intermediate
Phosphorylated
intermediate
Glutamine
(b) Conversion reaction coupled with ATP hydrolysis
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Figure 6.9c
GGlu  3.4 kcal/mol
GGlu  3.4 kcal/mol
 GATP  −7.3 kcal/mol
Net G  −3.9 kcal/mol
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GATP  −7.3 kcal/mol
(c) Free-energy change for coupled reaction
 ATP drives endergonic reactions by phosphorylation,
transferring a phosphate group to some other
molecule, such as a reactant
 The recipient molecule is now called a
phosphorylated intermediate
 ATP hydrolysis leads to a change in a protein’s
shape and often its ability to bind to another
molecule
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Figure 6.10
Transport protein
Solute
Solute transported
(a) Transport work: ATP phosphorylates transport proteins.
Vesicle
Motor protein
Cytoskeletal track
Protein and
vesicle moved
(b) Mechanical work: ATP binds noncovalently to motor proteins
and then is hydrolyzed.
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Figure 6.11
The Regeneration of ATP
Energy from
catabolism
(exergonic, energyreleasing processes)
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Energy for cellular
work (endergonic,
energy-consuming
processes)
10/21 Enzymes
Focus on:
1.) Catalysts
2.) Activation Energy
3.) Induced Fit
4.) Allosteric Sites
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Enzyme defined:
 A catalyst is a chemical agent that speeds up a
reaction without being consumed by the reaction
 An enzyme is a catalytic protein
 Hydrolysis of sucrose by the enzyme sucrase is an
example of an enzyme-catalyzed reaction
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Figure 6.UN02
Sucrase
Sucrose
(C12H22O11)
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Glucose
(C6H12O6)
Fructose
(C6H12O6)
Figure 6.12
A
B
C
D
Free energy
Transition state
A
B
C
D
EA
Reactants
A
B
G  0
C
D
Products
Progress of the reaction
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Enzymes catalyze reactions by lowering the
EA barrier
 Enzymes do not affect the change in free energy
(∆G); instead, they speed up reactions that would
occur eventually
Figure 6.13
Free energy
Course of
reaction
without
enzyme
EA
without
enzyme
EA with
enzyme
is lower
Reactants
G is unaffected
by enzyme
Course of
reaction
with enzyme
Products
Progress of the reaction
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Vocab: Substrate, enzyme-substrate complex,
active site
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 Enzymes change shape due to chemical
interactions with the substrate
 This induced fit of the enzyme to the substrate
brings chemical groups of the active site into
positions that enhance their ability to catalyze the
reaction
Video: Enzyme Induced Fit
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Figure 6.14
Substrate
Active site
Enzyme
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Enzyme-substrate
complex
How do you lower EA?
 The active site can lower an EA barrier by
 Orienting substrates correctly
 Straining substrate bonds
 Providing a favorable microenvironment
 Covalently bonding to the substrate
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Orienting substrates correctly
Straining substrate bonds
Providing a favorable
microenvironment
Figure 6.15-1
1 Substrates enter
active site.
Substrates
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2 Substrates are
held in active site by
weak interactions.
Enzyme-substrate
complex
Figure 6.15-2
1 Substrates enter
active site.
Substrates
2 Substrates are
held in active site by
weak interactions.
Enzyme-substrate
complex
3 Substrates are
converted to
products.
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Figure 6.15-3
2 Substrates are
held in active site by
weak interactions.
1 Substrates enter
active site.
Substrates
Enzyme-substrate
complex
4 Products are
released.
Products
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3 Substrates are
converted to
products.
Figure 6.15-4
2 Substrates are
held in active site by
weak interactions.
1 Substrates enter
active site.
Substrates
Enzyme-substrate
complex
5 Active
site is
available
for new
substrates.
Enzyme
4 Products are
released.
Products
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3 Substrates are
converted to
products.
Effects of Local Conditions on Enzyme Activity
 An enzyme’s activity can be affected by
 General environmental factors, such as
temperature and pH
 Chemicals that specifically influence the enzyme
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Figure 6.16
Rate of reaction
Optimal temperature for
typical human enzyme
(37C)
0
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
bacteria (77C)
40
80
60
Temperature (C)
(a) Optimal temperature for two enzymes
20
Rate of reaction
Optimal pH for pepsin
(stomach
enzyme)
0
1
2
3
5
pH
(b) Optimal pH for two enzymes
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4
120
100
Optimal pH for trypsin
(intestinal
enzyme)
6
7
8
9
10
Figure 6.16a
Rate of reaction
Optimal temperature for
typical human enzyme
(37C)
80
60
Temperature (C)
(a) Optimal temperature for two enzymes
0
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20
40
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
bacteria (77C)
100
120
Figure 6.16b
Rate of reaction
Optimal pH for pepsin
(stomach
enzyme)
0
1
2
3
5
pH
(b) Optimal pH for two enzymes
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4
Optimal pH for trypsin
(intestinal
enzyme)
6
7
8
9
10
Cofactors
 Cofactors are nonprotein enzyme helpers
 Cofactors may be inorganic (such as a metal in ionic
form) or organic
 An organic cofactor is called a coenzyme
 Coenzymes include vitamins
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Enzyme Inhibitors
 Competitive inhibitors bind to the active site of an
enzyme, competing with the substrate
 Noncompetitive inhibitors bind to another part of
an enzyme, causing the enzyme to change shape
and making the active site less effective
 Examples of inhibitors include toxins, poisons,
pesticides, and antibiotics
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Figure 6.17
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive
inhibition
Substrate
Active site
Competitive
inhibitor
Enzyme
Noncompetitive
inhibitor
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The Evolution of Enzymes
 Enzymes are proteins encoded by genes
 Changes (mutations) in genes lead to changes in
amino acid composition of an enzyme
 Altered amino acids in enzymes may alter their
substrate specificity
 Under new environmental conditions a novel form of
an enzyme might be favored
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Concept 6.5: Regulation of enzyme activity helps
control metabolism
 Chemical chaos would result if a cell’s metabolic
pathways were not tightly regulated
 A cell does this by switching on or off the genes that
encode specific enzymes or by regulating the
activity of enzymes
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Allosteric Regulation of Enzymes
 Allosteric regulation may either inhibit or stimulate
an enzyme’s activity
 Allosteric regulation occurs when a regulatory
molecule binds to a protein at one site and affects
the protein’s function at another site
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Allosteric Activation and Inhibition
 Most allosterically regulated enzymes are made from
polypeptide subunits
 Each enzyme has active and inactive forms
 The binding of an activator stabilizes the active form
of the enzyme
 The binding of an inhibitor stabilizes the inactive
form of the enzyme
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Figure 6.18
(a) Allosteric activators and inhibitors
Allosteric enzyme
with four subunits
Active site
(one of four)
Regulatory
site (one
Activator
of four)
Active form
Substrate
Stabilized
active form
Oscillation
Nonfunctional
active site
Inactive
form
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Inhibitor
(b) Cooperativity: another type of allosteric
activation
Stabilized
inactive form
Inactive form
Stabilized
active form
Figure 6.18a
(a) Allosteric activators and inhibitors
Allosteric enzyme
with four subunits
Regulatory
site (one
of four)
Active site
(one of four)
Activator
Active form
Stabilized
active form
Oscillation
Nonfunctional
active site
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Inactive
form
Inhibitor
Stabilized
inactive form
Figure 6.18b
(b) Cooperativity: another type of allosteric
activation
Substrate
Inactive form
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Stabilized
active form
 Cooperativity is a form of allosteric regulation that
can amplify enzyme activity
 One substrate molecule primes an enzyme to act
on additional substrate molecules more readily
 Cooperativity is allosteric because binding by a
substrate to one active site affects catalysis in a
different active site
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Feedback Inhibition
 In feedback inhibition, the end product of a
metabolic pathway shuts down the pathway
 Feedback inhibition prevents a cell from wasting
chemical resources by synthesizing more product
than is needed
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Figure 6.19
Active site available
Isoleucine
used up by
cell
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Intermediate A
Feedback
inhibition
Enzyme 2
Intermediate B
Enzyme 3
Isoleucine
binds to
allosteric
site.
Intermediate C
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine)
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Specific Localization of Enzymes Within the Cell
 Structures within the cell help bring order to
metabolic pathways
 Some enzymes act as structural components of
membranes
 In eukaryotic cells, some enzymes reside in specific
organelles; for example, enzymes for cellular
respiration are located in mitochondria
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Figure 6.20
Mitochondria
The matrix contains
enzymes in solution
that are involved in
one stage of cellular
respiration.
Enzymes for another
stage of cellular
respiration are
embedded in the
inner membrane.
1 m
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Figure 6.20a
The matrix contains
enzymes in solution
that are involved in
one stage of cellular
respiration.
Enzymes for another
stage of cellular
respiration are
embedded in the
inner membrane.
1 m
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Figure 6.UN03
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Figure 6.UN04
Free energy
Course of
reaction
without
enzyme
EA
without
enzyme
EA with
enzyme
is lower
Reactants
G is unaffected
by enzyme
Course of
reaction
with enzyme
Products
Progress of the reaction
© 2014 Pearson Education, Inc.