Enzyme 1

1
Enzyme 1
Enzyme 2
Enzyme 3
D
C
B
A
Reaction 1
Reaction 3
Reaction 2
Product
Starting molecule
2
Diving converts potential energy to kinetic
energy.
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.
A diver has less potential energy in the
water than on the platform.
3
Heat
CO2

Chemical energy
H2O
(a) First law of thermodynamics
(b) Second law of thermodynamics
4

• More free energy (higher G)
• Less stable
• Greater work capacity

In a spontaneous change

• The free energy of the system
• decreases (?G lt 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
5
Reactants
Amount of energy released (?G lt 0)
Energy
Free energy
Products
Progress of the reaction
(a) Exergonic reaction energy released
Products
Amount of energy required (?G gt 0)
Energy
Free energy
Reactants
Progress of the reaction
(b) Endergonic reaction energy required
6
?G lt 0
?G 0
(a) An isolated hydroelectric system
(b) An open hydroelectric system
?G lt 0
?G lt 0
?G lt 0
?G lt 0
(c) A multistep open hydroelectric system
7
Adenine
Phosphate groups
Ribose
8
P
P
P
Adenosine triphosphate (ATP)
H2O
P

P
P
Energy

i
Inorganic phosphate
Adenosine diphosphate (ADP)
9
NH2
NH3
?G 3.4 kcal/mol

Glu
Glu
Glutamic acid
Glutamine
Ammonia
(a) Endergonic reaction
P
ATP phosphorylates glutamic acid, making the
amino acid less stable.
1
ADP


ATP
Glu
Glu
NH2
P
Ammonia displaces the phosphate group, forming
glutamine.
2
NH3
P


i
Glu
Glu
(b) Coupled with ATP hydrolysis, an exergonic
reaction
(c) Overall free-energy change
10
Membrane protein
P
P
i
Solute
Solute transported
(a) Transport work ATP phosphorylates
transport proteins
ADP

ATP
P
i
Vesicle
Cytoskeletal track
ATP
Protein moved
Motor protein
(b) Mechanical work ATP binds noncovalently
to motor proteins, then is hydrolyzed
11
ATP

H2O
Energy for cellular work (endergonic, energy-consu
ming processes)
Energy from catabolism (exergonic, energy-releasin
g processes)
ADP
P

i
12
Sucrose (C12H22O11)
Sucrase
Glucose (C6H12O6)
Fructose (C6H12O6)
13
B
A
D
C
Transition state
EA
B
A
C
D
Free energy
Reactants
B
A
?G lt O
D
C
Products
Progress of the reaction
14
Course of reaction without enzyme
EA without enzyme
EA with enzyme is lower
Reactants
Free energy
Course of reaction with enzyme
?G is unaffected by enzyme
Products
Progress of the reaction
15
Substrate
Active site
Enzyme
Enzyme-substrate complex
(b)
(a)
16
Substrates enter active site enzyme
changes shape such that its active site enfolds
the substrates (induced fit).
1
Substrates held in active site by
weak interactions, such as hydrogen bonds
and ionic bonds.
2
Substrates
Enzyme-substrate complex
Active site can lower EA and speed up a
reaction.
3
6
Active site is available for two
new substrate molecules.
Enzyme
Products are released.
5
4
Substrates are converted to products.
Products
17
Optimal temperature for enzyme of thermophilic
(heat-tolerant) bacteria
Optimal temperature for typical human enzyme
Rate of reaction
0
20
40
80
60
100
Temperature (ºC)
(a) Optimal temperature for two enzymes
Optimal pH for pepsin (stomach enzyme)
Optimal pH for trypsin (intestinal enzyme)
Rate of reaction
5
4
3
2
1
0
6
7
8
9
10
pH
(b) Optimal pH for two enzymes
18
Substrate
Active site
Competitive inhibitor
Enzyme
Noncompetitive inhibitor
(a) Normal binding
(c) Noncompetitive inhibition
(b) Competitive inhibition
19
Allosteric enyzme with four subunits
Active site (one of four)
Regulatory site (one of four)
Activator
Active form
Stabilized active form
Oscillation
Non- functional active site
Inhibitor
Inactive form
Stabilized inactive form
(a) Allosteric activators and inhibitors
Substrate
Stabilized active form
Inactive form
(b) Cooperativity another type of allosteric
activation
20
Initial substrate (threonine)
Active site available
Threonine in active site
Enzyme 1 (threonine deaminase)
Isoleucine used up by cell
Intermediate A
Feedback inhibition
Enzyme 2
Active site of enzyme 1 no longer
binds threonine pathway is switched off.
Intermediate B
Enzyme 3
Intermediate C
Isoleucine binds to allosteric site
Enzyme 4
Intermediate D
Enzyme 5
End product (isoleucine)