Transcript (b) (a)

Enzyme 1
A
Reaction 1
Starting
molecule
Enzyme 2
B
Enzyme 3
C
Reaction 2
D
Reaction 3
Product
1
A diver has more potential
energy on the platform
than in the water.
Climbing up converts the kinetic
energy of muscle movement
to potential energy.
Diving converts
potential energy to
kinetic energy.
A diver has less potential
energy in the water
than on the platform.
2
Heat
Chemical
energy
(a) First law of thermodynamics
CO2
+
H2O
(b) Second law of thermodynamics
3
• 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
(b) Diffusion
(c) Chemical reaction
4
Reactants
Free energy
Amount of
energy
released
(∆G < 0)
Energy
Products
Progress of the reaction
(a) Exergonic reaction: energy released
Free energy
Products
Amount of
energy
required
(∆G > 0)
Energy
Reactants
Progress of the reaction
(b) Endergonic reaction: energy required
5
∆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
6
Adenine
Phosphate groups
Ribose
7
P
P
P
Adenosine triphosphate (ATP)
H2O
Pi
+
Inorganic phosphate
P
P
+
Energy
Adenosine diphosphate (ADP)
8
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
+ ADP
NH2
2 Ammonia displaces
the phosphate group,
forming glutamine.
P
Glu
+
NH3
Glu
+ Pi
(b) Coupled with ATP hydrolysis, an exergonic reaction
(c) Overall free-energy change
9
Membrane protein
P
Solute
Pi
Solute transported
(a) Transport work: ATP phosphorylates
transport proteins
ADP
+
ATP
Pi
Vesicle
Cytoskeletal track
ATP
Motor protein
Protein moved
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed
10
ATP + H2O
Energy from
catabolism (exergonic,
energy-releasing
processes)
ADP + P i
Energy for cellular
work (endergonic,
energy-consuming
processes)
11
Sucrose (C12H22O11)
Sucrase
Glucose (C6H12O6)
Fructose (C6H12O6)
12
A
B
C
D
Transition state
A
B
C
D
EA
Reactants
A
B
∆G < O
C
D
Products
Progress of the reaction
13
Course of
reaction
without
enzyme
EA
without
enzyme
EA with
enzyme
is lower
Reactants
Course of
reaction
with enzyme
∆G is unaffected
by enzyme
Products
Progress of the reaction
14
Substrate
Active site
Enzyme
(a)
Enzyme-substrate
complex
(b)
15
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.
Substrates
Enzyme-substrate
complex
3 Active site can lower EA
and speed up a reaction.
6 Active
site is
available
for two new
substrate
molecules.
Enzyme
5 Products are
released.
4 Substrates are
converted to
products.
Products
16
Rate of reaction
Optimal temperature for
typical human enzyme
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
bacteria
40
60
80
Temperature (ºC)
(a) Optimal temperature for two enzymes
0
20
Optimal pH for pepsin
(stomach enzyme)
100
Optimal pH
for trypsin
Rate of reaction
(intestinal
enzyme)
4
5
pH
(b) Optimal pH for two enzymes
0
1
2
3
6
7
8
9
10
17
Substrate
Active site
Competitive
inhibitor
Enzyme
Noncompetitive inhibitor
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive inhibition
18
Active site
Allosteric enyzme
with four subunits (one of four)
Regulatory
site (one
of four)
Activator
Active form
Stabilized active form
Oscillation
NonInhibitor
functional Inactive form
active
site
Stabilized inactive
form
(a) Allosteric activators and inhibitors
Substrate
Inactive form
Stabilized active
form
(b) Cooperativity: another type of allosteric activation
19
Initial substrate
(threonine)
Active site
available
Isoleucine
used up by
cell
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Intermediate A
Feedback
inhibition
Isoleucine
binds to
allosteric
site
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
End product
(isoleucine)
20