2. An organism’s metabolism transforms matter and
energy, subject to the laws of thermodynamics
• Metabolism is the totality of an organism’s chemical
reactions
– Example of an emergent property that arises from
interactions between molecules within the cell
• A metabolic pathway begins with a specific molecule and
ends with a product
– Each step is catalyzed by a specific enzyme
Enzyme 1 Enzyme 2 Enzyme 3
A B C D
Reaction 1 Reaction 2 Reaction 3
Starting Product
molecule
5. A diver has more potential energy Diving converts potential energy
on the platform than in the water. to kinetic energy.
Climbing up converts the kinetic energy A diver has less potential energy
of muscle movement to potential energy. in the water than on the platform.
12. Relationship of free energy to stability, work capacity and
spontaneous change
Unstable systems
• 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
(c) Chemical reaction
(a) Gravitational motion (b) Diffusion
14. Fig. 8-6
Reactants
Amount of
energy
released
Exergonic reation:
Free energy
(∆G < 0)
energy released Energy
Products
Progress of the reaction
Products
Amount of
energy
Endergonic reation: required
Free energy
(∆G > 0)
energy required Energy
Reactants
Progress of the reaction
16. Fig. 8-7
∆G < 0 ∆G = 0
An isolated hydroelectric system
•Downhill flow of water turns a turbine
•turbine drives a generator
•Electricity turns on a light bulb
•Eventually equilibrium will be reached Spontaneous reaction
(b) An open hydroelectric system ∆G < 0
•Running water powers the generator
•Intake and outflow of water keeps equilibrium from occurring
•Electricity turns on a light bulb
c) A multistep open hydroelectric ∆G < 0
system ∆G < 0
•Running water powers the generator ∆G < 0
•The product becomes the reactant in the
next reaction
•Equilibrium will not be reached
•Ex: cellular respiration
Similar to a catabolic pathway that releases energy
17. Practice Quiz A B
• Which one of these is the best example of a
spontaneous reaction?
• Which one is more unstable?
• Which reaction is uphill? Which is downhill?
• Which reaction is endergonic? Exergonic?
• Which one will require more energy for work?
Stable Unstable
• Which one has a +∆G? Uphill Downhill
Less work More work
• Which one has a -∆G? Low ∆G High ∆G
∆G increases ∆G decreases
• In B, is the ∆G going to decrease or increase? Nonspontaneous Spontaneous
Endergonic Exergonic
Absorbs energy Releases energy
21. Fig. 8-9
P P P
Adenosine triphosphate (ATP)
H2O
Pi + P P + Energy
Inorganic
phosphate
Adenosine diphosphate (ADP)
ATP + H20 ADP + Pi
∆G = -7.3 kcal/mol
Exergonic
23. NH2
(a) Endergonic reaction
NH3
Glu + ∆G = +3.4 kcal/mol
Glu
Glutamic Ammonia Glutamine
acid
P
(b) Coupled with ATP hydrolysis, + + ADP
an exergonic reaction ATP
Glu Glu
1 ATP phosphorylates glutamic acid,
making the amino acid less stable NH2
(exergonic).
P
2 Ammonia displaces the phosphate + NH3
+ Pi
group, forming glutamine. Glu Glu
(c) Overall free-energy change
Overall exergonic
reaction with energy
coupling
24. Fig. 8-11
Membrane protein
) Transport work:
TP phosphorylates
ansport proteins
P Pi
Solute Solute transported
ADP
ATP +
Pi
Cytoskeletal track
(b) Mechanical work:
ATP binds non-
covalently to motor ATP
proteins, then is
hydrolyzed
Motor protein Protein moved
26. Fig. 8-12
Energy coupling and the renewal of ATP
ATP synthesis ATP hydrolysis
requires energy releases energy
(endergonic) (exergonic)
ATP + H2O
Energy from Energy for cellular
catabolism work (endergonic,
(exergonic, energy-consuming
energy-releasing ADP + P i
processes)
processes)
Exergonic reactions drive the formation of ATP (endergonic)
Endergonic reactions driven by hydrolysis of ATP (exergonic)
29. Fig. 8-14
Energy profile of an exergonic reaction (spontaneous)
AB + CD AC + BD
A B
Unstable transition state
C D
A B EA Determines the rate of the rxn
Free energy
C D
Reactants
A B
∆G < O
C D
Products
Progress of the reaction
30. Fig. 8-15
The effect of an enzyme on activation energy
Course of
reaction EA
without
enzyme without EA with
enzyme enzyme
is lower
Free energy
Reactants
Course of ∆G is unaffected
reaction by enzyme
with enzyme
Products
Progress of the reaction
32. Fig. 8-16
Induced fit between an enzyme and its substrate
Substrate
Active site
Enzyme Enzyme-substrate
complex
The active site is the region on the enzyme where the substrate binds.
An enzyme’s recognition of a substrate is very specific due to it AA sequence.
34. Fig. 8-17
1 Substrates enter active site; enzyme
changes shape such that its active site 2 Substrates held in
enfolds the substrates (induced fit). 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 4 Substrates are
released. converted to
products.
Products
37. Fig. 8-18
Optimal temperature for Optimal temperature for
typical human enzyme enzyme of thermophilic
(heat-tolerant)
Rate of reaction
bacteria
40
0 60
20 80 100
Temperature (ºC)
(a) Optimal temperature for two enzymes
Optimal pH for pepsin Optimal pH
(stomach enzyme) for trypsin
(intestinal
Rate of reaction
enzyme)
0 41 5 2 3 6 7 8 9 10
pH
(b) Optimal pH for two enzymes
39. Fig. 8-19
Types of Enzyme Inhibition
Substrate
Active site
Competitive
inhibitor
Enzyme
Noncompetitive inhibitor
(a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition –
The shape of the enzyme is
changed
42. Allosteric Regulation of Enzymes
tors and inhibitors (bind to regulatory sites)
Allosteric enyzme Active site
with four subunits (one of four)
(b) Cooperativity
Regulatory (substrate binds to active site)
site (one
of four) Activator Substrate
Active form Stabilized active form
Oscillation
Inactive form Stabilized active
form
Non-
functional Inactive form Inhibitor Stabilized inactive
active form
site
Fig. 8-20
43. Initial substrate
Feedback Active site
(threonine)
Inhibition available
Threonine
in active site
in isoleucine Enzyme 1
(threonine
synthesis Isoleucine
used up by
deaminase)
cell
Intermediate A
As isoleucine
Feedback
accumulates, inhibition Enzyme 2
it slows down its
Intermediate B
own synthesis by
allosterically Enzyme 3
inhibiting the
enzyme for the first Active site of
Intermediate C
Isoleucine
step of the pathway binds to enzyme 1 no Enzyme 4
allosteric longer binds
site threonine;
pathway is Intermediate D
switched off.
Enzyme 5
End product
(isoleucine)
Fig. 8-22
44. Practice Quiz
1. Lists the three components of ATP.
2. ________ reactions release energy while ________ reactions absorb
energy
3. Cells get energy from __________ to synthesize ATP from ADP and Pi.
– Anabolic pathways, catabolic pathways, feedback inhibition, regeneration
1. Explain how energy coupling works.
2. True of False: ATP hydrolysis is exergonic and spontaneous.
3. Enzymes lower the ________ of a chemical reaction.
4. True or False: ∆G is decreased when an enzyme is present.
5. When a protein is __________ it can become more unstable. Thus the
energy from its removal can drive endergonic reactions.
6. List the three types of work that ATP does.
Hinweis der Redaktion
Figure 8.2 Transformations between potential and kinetic energy
Figure 8.3 The two laws of thermodynamics
Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change
Figure 8.6 Free energy changes ( Δ G ) in exergonic and endergonic reactions
Figure 8.7 Equilibrium and work in isolated and open systems
For the Cell Biology Video Space Filling Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
For the Cell Biology Video Stick Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
Figure 8.9 The hydrolysis of ATP
Figure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis
Figure 8.11 How ATP drives transport and mechanical work
Figure 8.12 The ATP cycle
Figure 8.14 Energy profile of an exergonic reaction
Figure 8.15 The effect of an enzyme on activation energy
For the Cell Biology Video Closure of Hexokinase via Induced Fit, go to Animation and Video Files.
Figure 8.16 Induced fit between an enzyme and its substrate
Figure 8.17 The active site and catalytic cycle of an enzyme