Download Ch.08An Introduction to Metabolism

A diver has more potential
energy on the platform
than in the water.
Enzyme 1
Enzyme 2
B
A
Reaction 1
Starting
molecule
Reaction 2
Diving converts
potential energy to
kinetic energy.
Enzyme 3
C
D
Reaction 3
Product
Climbing up converts the kinetic
energy of muscle movement
to potential energy.
A diver has less potential
energy in the water
than on the platform.
1
2
•  More free energy (higher G)
•  Less stable
•  Greater work capacity Heat
Chemical
energy
(a) First law of thermodynamics
CO2
+
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
H 2O
•  Less free energy (lower G)
•  More stable
•  Less work capacity (b) Second law of thermodynamics
(b) Diffusion
(a) Gravitational motion
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∆G < 0
Reactants
(c) Chemical reaction
∆G = 0
Free energy
Amount of
energy
released
(∆G < 0)
Energy
Products
(a) An isolated hydroelectric system
(b) An open hydroelectric
system
Progress of the reaction
∆G < 0
(a) Exergonic reaction: energy released
Free energy
Products
Energy
Amount of
energy
required
(∆G > 0)
∆G < 0
∆G < 0
∆G < 0
Reactants
Progress of the reaction
(b) Endergonic reaction: energy required
(c) A multistep open hydroelectric system
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P
Adenine
P
P
Adenosine triphosphate (ATP)
H 2O
Phosphate groups
Ribose
Pi
+
P
P
Inorganic phosphate
+
Energy
Adenosine diphosphate (ADP)
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Membrane protein
NH2
Glu
Glutamic
acid
NH3
+
∆G = +3.4 kcal/mol
Glu
Ammonia
Glutamine
(a) Endergonic reaction
1 ATP phosphorylates
glutamic acid,
making the amino
acid less stable.
P
+
Glu
ATP
Glu
Solute
+ ADP
P
Glu
+
Glu
ADP
+
ATP
Vesicle
NH3
Solute transported
(a) Transport work: ATP phosphorylates
transport proteins
NH2
2 Ammonia displaces
the phosphate group,
forming glutamine.
Pi
P
Cytoskeletal track
Pi
+ Pi
(b) Coupled with ATP hydrolysis, an exergonic reaction
ATP
Motor protein
Protein moved
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed
(c) Overall free-energy change
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ATP + H2O
Sucrose (C12H22O11)
Sucrase
Energy from
catabolism (exergonic,
energy-releasing
processes)
ADP + P i
Energy for cellular
work (endergonic,
energy-consuming
processes)
Glucose (C6H12O6)
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Fructose (C6H12O6)
12
A
B
C
D
Course of
reaction
without
enzyme
A
B
C
D
EA
without
enzyme
EA with
enzyme
is lower
EA
Free energy
Free energy
Transition state
Reactants
A
B
C
D
∆G < O
Reactants
Course of
reaction
with enzyme
∆G is unaffected
by enzyme
Products
Products
Progress of the reaction
Progress of the reaction
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1 Substrates enter active site; enzyme
changes shape such that its active site
enfolds the substrates (induced fit).
2 Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds.
Substrate
Substrates
Enzyme-substrate
complex
3 Active site can lower EA
and speed up a reaction.
Active site
6 Active
site is
available
for two new
substrate
molecules.
Enzyme
Enzyme
(a)
Enzyme-substrate
complex
(b)
5 Products are
released.
4 Substrates are
converted to
products.
Products
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Rate of reaction
Optimal temperature for
typical human enzyme
16
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
bacteria
Substrate
40
60
80
Temperature (ºC)
(a) Optimal temperature for two enzymes
0
20
Rate of reaction
Optimal pH for pepsin
(stomach enzyme)
4
5
0
1
2
3
pH
(b) Optimal pH for two enzymes
100
Active site
Competitive
inhibitor
Enzyme
Optimal pH
for trypsin
(intestinal
enzyme)
Noncompetitive inhibitor
(a) Normal binding
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7
8
9
(b) Competitive inhibition
(c) Noncompetitive inhibition
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Allosteric enyzme Active site
with four subunits (one of four)
Initial substrate
(threonine)
Active site
available
Regulatory
site (one
of four)
Activator
Active form
Stabilized active form
Isoleucine
used up by
cell
Oscillation
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Intermediate A
Feedback
inhibition
NonInhibitor
functional Inactive form
active
site
Stabilized inactive
form
Isoleucine
binds to
allosteric
site
(a) Allosteric activators and inhibitors
Substrate
Enzyme 2
Active site of
enzyme 1 no
longer binds Intermediate B
threonine;
pathway is
Enzyme 3
switched off.
Intermediate C
Enzyme 4
Intermediate D
Enzyme 5
Inactive form
Stabilized active
form
End product
(isoleucine)
(b) Cooperativity: another type of allosteric activation
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