1. 8 An Introduction to Metabolism8
An Introduction to Metabolism
Lecture Presentation by Nicole Tunbridge and
Kathleen Fitzpatrick

2. The Energy of Life
The living cell is a miniature chemical factory where thousands of reactions occur
The cell extracts energy stored in sugars and other fuels and applies energy to perform work
Some organisms even convert energy to light, as in bioluminescence

3. Figure 8.1
Figure 8.1 What causes these breaking waves to glow?

4. Figure 8.1a
Figure 8.1a What causes these breaking waves to glow? (part 1: bioluminescent fungus)

5. Concept 8.1: An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics
Metabolism is the totality of an organism’s chemical reactions
Metabolism is an emergent property of life that arises from orderly interactions between molecules

6. Organization of the Chemistry of Life into Metabolic Pathways
A metabolic pathway begins with a specific molecule and ends with a product
Each step is catalyzed by a specific enzyme

7. A B C D Starting molecule
Figure 8.UN01
Enzyme 1
Enzyme 2
Enzyme 3 A B C D
Reaction 1
Reaction 2
Reaction 3
Starting
molecule
Product
Figure 8.UN01 In-text figure, generalized metabolic pathway, p. 142

8. 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

9. 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 energy flows through living organisms

10. Forms of Energy Energy is the capacity to cause change
Energy exists in various forms, some of which can perform work

11. Kinetic energy is energy associated with motion
Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules
Potential energy is energy that matter possesses because of its location or structure
Chemical energy is potential energy available for release in a chemical reaction
Energy can be converted from one form to another

12. A diver has more potential energy on the platform than in the water.
Figure 8.2
A diver has more potential
energy on the platform
than in the water.
Diving converts
potential energy to
kinetic energy.
Figure 8.2 Transformations between potential and kinetic energy
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.

13. Animation: Energy Concepts

14. 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 unable to exchange energy or matter with its surroundings
In an open system, energy and matter can be transferred between the system and its surroundings
Organisms are open systems

15. 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

16. Second law of thermodynamics
Figure 8.3
Heat
CO2
H2O
Chemical
energy
(a)
First law of thermo-
dynamics
Figure 8.3 The two laws of thermodynamics
(b)
Second law of thermodynamics

17. First law of thermodynamics
Figure 8.3a
Chemical
energy
Figure 8.3a The two laws of thermodynamics (part 1: conservation)
(a)
First law of thermodynamics

18. Second law of thermodynamics
Figure 8.3b
Heat
CO2
H2O
Figure 8.3b The two laws of thermodynamics (part 2: entropy)
(b)
Second law of thermodynamics

19. 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 (disorder) of the universe

20. 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

21. 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

22. Figure 8.4
Figure 8.4 Order as a characteristic of life

23. Figure 8.4a
Figure 8.4a Order as a characteristic of life (part 1: sea urchin)

24. Figure 8.4b
Figure 8.4b Order as a characteristic of life (part 2: succulent)

25. 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

26. Concept 8.2: 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

27. Free-Energy Change, G
A living system’s free energy is energy that can do work when temperature and pressure are uniform, as in a living cell

28. The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin units (T)
∆G = ∆H - T∆S
Only processes with a negative ∆G are spontaneous
Spontaneous processes can be harnessed to perform work

29. Free Energy, Stability, and Equilibrium
Free energy is a measure of a system’s instability, its tendency to change to a more stable state
During a spontaneous change, free energy decreases and the stability of a system increases
Equilibrium is a state of maximum stability
A process is spontaneous and can perform work only when it is moving toward equilibrium

30. • More free energy (higher G) • Less stable • Greater work capacity
Figure 8.5
• 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
Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change
• Less free energy (lower G)
• More stable
• Less work capacity
(a) Gravitational motion
(b) Diffusion
(c) Chemical reaction

31. • More free energy (higher G) • Less stable • Greater work capacity
Figure 8.5a
• 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
Figure 8.5a The relationship of free energy to stability, work capacity, and spontaneous change (part 1: summary)
• Less free energy (lower G)
• More stable
• Less work capacity

32. (a) Gravitational motion (b) Diffusion (c) Chemical reaction
Figure 8.5b
Figure 8.5b The relationship of free energy to stability, work capacity, and spontaneous change (part 2: examples)
(a) Gravitational motion
(b) Diffusion
(c) Chemical reaction

33. Free Energy and Metabolism
The concept of free energy can be applied to the chemistry of life’s processes

34. Exergonic and Endergonic Reactions in Metabolism
An exergonic reaction proceeds with a net release of free energy and is spontaneous
An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous

35. Exergonic reaction: energy released, spontaneous
Figure 8.6
(a)
Exergonic reaction: energy released,
spontaneous
Reactants
Amount of
energy
released
(∆G < 0)
Free energy
Energy
Products
Progress of the reaction
(b)
Endergonic reaction: energy required,
nonspontaneous
Products
Figure 8.6 Free energy changes (∆G) in exergonic and endergonic reactions
Amount of
energy
required
(∆G > 0)
Free energy
Energy
Reactants
Progress of the reaction

36. Exergonic reaction: energy released, spontaneous
Figure 8.6a
(a)
Exergonic reaction: energy released,
spontaneous
Reactants
Amount of
energy
released
(∆G < 0)
Free energy
Energy
Products
Figure 8.6a Free energy changes (∆G) in exergonic and endergonic reactions (part 1: exergonic)
Progress of the reaction

37. Endergonic reaction: energy required, nonspontaneous
Figure 8.6b
(b)
Endergonic reaction: energy required,
nonspontaneous
Products
Amount of
energy
required
(∆G > 0)
Free energy
Energy
Reactants
Figure 8.6b Free energy changes (∆G) in exergonic and endergonic reactions (part 2: endergonic)
Progress of the reaction

38. Equilibrium and Metabolism
Reactions in a closed system eventually reach equilibrium and then do no work

39. Figure 8.7
∆G < 0
∆G = 0
Figure 8.7 Equilibrium and work in an isolated hydroelectric system

40. Cells are not in equilibrium; they are open systems experiencing a constant flow of materials
A defining feature of life is that metabolism is never at equilibrium
A catabolic pathway in a cell releases free energy in a series of reactions

41. ∆G < 0 ∆G < 0 ∆G < 0 ∆G < 0
Figure 8.8
(a)
An open hydro-
electric system
∆G < 0
∆G < 0
∆G < 0
∆G < 0
Figure 8.8 Equilibrium and work in open systems
(b) A multistep open hydroelectric system

42. Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions
A cell does three main kinds of work
Chemical
Transport
Mechanical
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

43. The Structure and Hydrolysis of ATP
ATP (adenosine triphosphate) is the cell’s energy shuttle
ATP is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups

44. Adenosine diphosphate
Figure 8.9
Adenine
Triphosphate group
(3 phosphate groups)
Ribose
(a) The structure of ATP
Adenosine triphosphate (ATP)
H2O
Figure 8.9 The structure and hydrolysis of adenosine triphosphate (ATP)
Energy
Inorganic
phosphate
Adenosine diphosphate
(ADP)
(b) The hydrolysis of ATP

45. Triphosphate group (3 phosphate groups)
Figure 8.9a
Adenine
Triphosphate group
(3 phosphate groups)
Ribose
Figure 8.9a The structure and hydrolysis of adenosine triphosphate (ATP) (part 1: structure)
(a) The structure of ATP

46. Adenosine diphosphate
Figure 8.9b
Adenosine triphosphate (ATP)
H2O
Energy
Figure 8.9b The structure and hydrolysis of adenosine triphosphate (ATP) (part 2: hydrolysis)
Inorganic
phosphate
Adenosine diphosphate
(ADP)
(b) The hydrolysis of ATP

47. Video: Space-Filling Model of ATP

48. Video: Stick Model of ATP

49. The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis
Energy is released from ATP when the terminal phosphate bond is broken
This release of energy comes from the chemical change to a state of lower free energy, not from the phosphate bonds themselves

50. How the Hydrolysis of ATP Performs Work
The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP
In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction
Overall, the coupled reactions are exergonic

51. 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

52. i i ∆GGlu = +3.4 kcal/mol Glutamic acid Ammonia Glutamine
Figure 8.10
NH3
NH2
∆GGlu
= +3.4 kcal/mol
Glu
Glu
Glutamic acid
Ammonia
Glutamine
(a) Glutamic acid conversion to glutamine
NH3 P 1 2
NH2
ADP
ADP P i
Glu
ATP
Glu
Glu
Glutamic acid
Phosphorylated
intermediate
Glutamine
(b) Conversion reaction coupled with ATP hydrolysis
∆GGlu
= +3.4 kcal/mol
Figure 8.10 How ATP drives chemical work: energy coupling using ATP hydrolysis
NH3
NH2
ATP
ADP P i
Glu
Glu
∆GGlu
= +3.4 kcal/mol
∆GATP
= −7.3 kcal/mol
+ ∆GATP
= −7.3 kcal/mol
Net ∆G
= −3.9 kcal/mol
(c) Free-energy change for coupled reaction

53. (a) Glutamic acid conversion to glutamine
Figure 8.10a
NH3
NH2
Glu
Glu
Glutamic acid
Ammonia
Glutamine
∆GGlu
= +3.4 kcal/mol
(a) Glutamic acid conversion to glutamine
Figure 8.10a How ATP drives chemical work: energy coupling using ATP hydrolysis (part 1: nonspontaneous reaction)

54. Phosphorylated intermediate Phosphorylated intermediate
Figure 8.10b P 1
ADP
ATP
Glu
Glu
Glutamic acid
Phosphorylated
intermediate
NH3 P 2
NH2
ADP
ADP P i
Glu
Glu
Figure 8.10b How ATP drives chemical work: energy coupling using ATP hydrolysis (part 2: coupled reaction)
Phosphorylated
intermediate
Glutamine
(b) Conversion reaction coupled with ATP hydrolysis

55. i ∆GGlu = +3.4 kcal/mol ADP P ∆GGlu = +3.4 kcal/mol ∆GATP
Figure 8.10c
∆GGlu
= +3.4 kcal/mol
NH3
NH2
ATP
ADP P i
Glu
Glu
∆GGlu
= +3.4 kcal/mol
∆GATP
= −7.3 kcal/mol
+ ∆GATP
= −7.3 kcal/mol
Figure 8.10c How ATP drives chemical work: energy coupling using ATP hydrolysis (part 3: free energy change)
Net ∆G
= −3.9 kcal/mol
(c) Free-energy change for coupled reaction

56. Transport and mechanical work in the cell are also powered by ATP hydrolysis
ATP hydrolysis leads to a change in protein shape and binding ability

57. (a) Transport work: ATP phosphorylates transport proteins.
Figure 8.11
Transport protein
Solute
ATP
ADP P i P P i
Solute transported
(a) Transport work: ATP phosphorylates transport proteins.
Vesicle
Cytoskeletal track
Figure 8.11 How ATP drives transport and mechanical work
ATP
ADP P
ATP i
Motor protein
Protein and vesicle moved
(b)
Mechanical work: ATP binds noncovalently to motor
proteins and then is hydrolyzed.

58. The Regeneration of ATP
ATP is a renewable resource that is regenerated by addition of a phosphate group to adenosine diphosphate (ADP)
The energy to phosphorylate ADP comes from catabolic reactions in the cell
The ATP cycle is a revolving door through which energy passes during its transfer from catabolic to anabolic pathways

59. ATP H2O Energy from catabolism (exergonic, energy-
Figure 8.12
ATP
H2O
Energy from
catabolism
(exergonic, energy-
releasing processes)
Energy for cellular
work (endergonic
energy-consuming
processes)
Figure 8.12 The ATP cycle
ADP P i

60. Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers
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

61. Sucrase Sucrose (C12H22O11) Glucose (C6H12O6) Fructose (C6H12O6)
Figure 8.UN02
Sucrase
Sucrose
(C12H22O11)
Glucose
(C6H12O6)
Fructose
(C6H12O6)
Figure 8.UN02 In-text figure, sucrose hydrolysis, p.151

62. The Activation Energy Barrier
Every chemical reaction between molecules involves bond breaking and bond forming
The initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (EA)
Activation energy is often supplied in the form of thermal energy that the reactant molecules absorb from their surroundings

63. Progress of the reaction
Figure 8.13 A B C D
Transition state A B EA
Free energy C D
Reactants A B
Figure 8.13 Energy profile of an exergonic reaction
∆G < O C D
Products
Progress of the reaction

64. Animation: How Enzymes Work

65. How Enzymes Speed Up Reactions
Enzymes catalyze reactions by lowering the EA barrier
Enzymes do not affect the change in free energy (∆G); instead, they hasten reactions that would occur eventually

66. Progress of the reaction
Figure 8.14
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
Figure 8.14 The effect of an enzyme on activation energy
Products
Progress of the reaction

67. Substrate Specificity of Enzymes
The reactant that an enzyme acts on is called the enzyme’s substrate
The enzyme binds to its substrate, forming an enzyme-substrate complex
The reaction catalyzed by each enzyme is very specific

68. The active site is the region on the enzyme where the substrate binds
Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction

69. Substrate Active site Enzyme Enzyme-substrate complex Figure 8.15
Figure 8.15 Induced fit between an enzyme and its substrate
Enzyme
Enzyme-substrate
complex

70. Video: Closure of Hexokinase Via Induced Fit

71. Catalysis in the Enzyme’s Active Site
In an enzymatic reaction, the substrate binds to the active site of the enzyme
The active site can lower an EA barrier by
Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment
Covalently bonding to the substrate

72. Substrates enter active site. Substrates are held in active
Figure 1
Substrates enter
active site. 2
Substrates are
held in active
site by weak
interactions.
Substrates
Enzyme-substrate
complex
Figure The active site and catalytic cycle of an enzyme (step 1)

73. Substrates enter active site. Substrates are held in active
Figure 1
Substrates enter
active site. 2
Substrates are
held in active
site by weak
interactions.
Substrates
Enzyme-substrate
complex
Figure The active site and catalytic cycle of an enzyme (step 2) 3
Substrates are
converted to
products.

74. Substrates enter active site. Substrates are held in active
Figure 1
Substrates enter
active site. 2
Substrates are
held in active
site by weak
interactions.
Substrates
Enzyme-substrate
complex
Figure The active site and catalytic cycle of an enzyme (step 3) 4
Products are
released. 3
Substrates are
converted to
products.
Products

75. Substrates enter active site. Substrates are held in active
Figure 1
Substrates enter
active site. 2
Substrates are
held in active
site by weak
interactions.
Substrates
Enzyme-substrate
complex 5
Active site
is available
for new
substrates.
Figure The active site and catalytic cycle of an enzyme (step 4)
Enzyme 4
Products are
released. 3
Substrates are
converted to
products.
Products

76. 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

77. Effects of Temperature and pH
Each enzyme has an optimal temperature in which it can function
Each enzyme has an optimal pH in which it can function
Optimal conditions favor the most active shape for the enzyme molecule

78. Optimal temperature for typical human enzyme (37C)
Figure 8.17
Optimal temperature for
typical human enzyme
(37C)
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
bacteria (77C)
Rate of reaction 20 40 60 80
100
120
Temperature (C)
(a) Optimal temperature for two enzymes
Optimal pH for pepsin
(stomach
enzyme)
Optimal pH for trypsin
(intestinal
enzyme)
Figure 8.17 Environmental factors affecting enzyme activity
Rate of reaction 1 2 3 4 5 6 7 8 9 10 pH
(b) Optimal pH for two enzymes

79. Optimal temperature for typical human enzyme Optimal temperature for
Figure 8.17a
Optimal temperature for
typical human enzyme
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
(37C)
bacteria (77C)
Rate of reaction
Figure 8.17a Environmental factors affecting enzyme activity (part 1: temperature) 20 40 60 80
100
120
Temperature (C)
(a) Optimal temperature for two enzymes

80. (b) Optimal pH for two enzymes
Figure 8.17b
Optimal pH for pepsin
(stomach
enzyme)
Optimal pH for trypsin
(intestinal
enzyme)
Rate of reaction
Figure 8.17b Environmental factors affecting enzyme activity (part 2: pH) 1 2 3 4 5 6 7 8 9 10 pH
(b) Optimal pH for two enzymes

81. 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

82. 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

83. (b) Competitive inhibition (c) Noncompetitive inhibition
Figure 8.18
(a) Normal binding
(b) Competitive inhibition
(c)
Noncompetitive
inhibition
Substrate
Active site
Competitive
inhibitor
Enzyme
Figure 8.18 Inhibition of enzyme activity
Noncompetitive
inhibitor

84. 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 result in novel enzyme activity or altered substrate specificity
Under new environmental conditions a novel form of an enzyme might be favored
For example, six amino acid changes improved substrate binding and breakdown in E. coli

85. Two changed amino acids were found near the active site. Active site
Figure 8.19
Two changed amino acids were
found near the active site.
Active site
Figure 8.19 Mimicking evolution of an enzyme with a new function
Two changed amino acids
were found in the active site.
Two changed amino acids
were found on the surface.

86. Concept 8.5: 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

87. 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

88. 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

89. (a) Allosteric activators and inhibitors
Figure 8.20
(a) Allosteric activators and inhibitors
(b) Cooperativity: another type of allosteric activation
Allosteric enzyme
with four subunits
Active site
(one of four)
Substrate
Regulatory
site (one
of four)
Activator
Active form
Stabilized
active form
Inactive form
Stabilized
active form
Oscillation
Non-
functional
active site
Figure 8.20 Allosteric regulation of enzyme activity
Inhibitor
Inactive form
Stabilized
inactive form

90. 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

91. 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

92. Active site available Threonine in active site Enzyme 1 (threonine
Figure 8.21
Active site available
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Isoleucine
used up by
cell
Intermediate A
Feedback
inhibition
Active
site no
longer
available;
pathway
is halted.
Enzyme 2
Intermediate B
Enzyme 3
Intermediate C
Isoleucine
binds to
allosteric
site.
Enzyme 4
Figure 8.21 Feedback inhibition in isoleucine synthesis
Intermediate D
Enzyme 5
End product
(isoleucine)

93. 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

94. enzymes in solution that are involved on one stage
Figure 8.22
Mitochondria
The matrix contains
enzymes in solution that
are involved on one stage
of cellular respiration.
Figure 8.22 Organelles and structural order in metabolism
Enzymes for another
stage of cellular
respiration are
embedded in the
inner membrane
1 µm

95. enzymes in solution that are involved in one stage
Figure 8.22a
The matrix contains
enzymes in solution that
are involved in one stage
of cellular respiration.
Figure 8.22a Organelles and structural order in metabolism (part 1: TEM)
Enzymes for another
stage of cellular
respiration are
embedded in the inner membrane.
1 µm

96. Figure 8.UN03a
Figure 8.UN03a Skills exercise: making a line graph and calculating a slope (part 1)

97. Figure 8.UN03b
Figure 8.UN03b Skills exercise: making a line graph and calculating a slope (part 2)

98. Progress of the reaction
Figure 8.UN04
Course of
reaction
without
enzyme EA
without
enzyme
EA with
enzyme
is lower
Reactants
Free energy
∆G is unaffected
by enzyme
Course of
reaction
with enzyme
Figure 8.UN04 Summary of key concepts: enzymes and activation energy
Products
Progress of the reaction

99. Figure 8.UN05
Figure 8.UN05 Test your understanding, question 11 (energy conversions)