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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserma...
Overview: The Energy of Life
• The living cell is a miniature chemical factory
where thousands of reactions occur
• The ce...
Figure 8.1
Concept 8.1: An organism’s metabolism
transforms matter and energy, subject to the
laws of thermodynamics
• Metabolism is ...
Organization of the Chemistry of Life into
Metabolic Pathways
• A metabolic pathway begins with a specific
molecule and en...
Figure 8.UN01
Enzyme 1 Enzyme 2 Enzyme 3
Reaction 1 Reaction 2 Reaction 3
ProductStarting
molecule
A B C D
• Catabolic pathways release energy by
breaking down complex molecules into
simpler compounds
• Cellular respiration, the ...
• Anabolic pathways consume energy to build
complex molecules from simpler ones
• The synthesis of protein from amino acid...
Forms of Energy
• Energy is the capacity to cause change
• Energy exists in various forms, some of which
can perform work
...
• Kinetic energy is energy associated with motion
• Heat (thermal energy) is kinetic energy
associated with random movemen...
Figure 8.2
A diver has more potential
energy on the platform
than in the water.
Diving converts
potential energy to
kineti...
The Laws of Energy Transformation
• Thermodynamics is the study of energy
transformations
• A isolated system, such as tha...
The First Law of Thermodynamics
• According to the first law of thermodynamics,
the energy of the universe is constant
– E...
The Second Law of Thermodynamics
• During every energy transfer or transformation,
some energy is unusable, and is often l...
Figure 8.3
(a) First law of thermodynamics (b) Second law of thermodynamics
Chemical
energy
Heat
Figure 8.3a
(a) First law of thermodynamics
Chemical
energy
Figure 8.3b
(b) Second law of thermodynamics
Heat
• Living cells unavoidably convert organized
forms of energy to heat
• Spontaneous processes occur without
energy input; t...
Biological Order and Disorder
• Cells create ordered structures from less
ordered materials
• Organisms also replace order...
Figure 8.4
Figure 8.4a
Figure 8.4b
• The evolution of more complex organisms does
not violate the second law of thermodynamics
• Entropy (disorder) may decre...
Concept 8.2: The free-energy change of a
reaction tells us whether or not the reaction
occurs spontaneously
• Biologists w...
Free-Energy Change, ∆G
• A living system’s free energy is energy that
can do work when temperature and pressure
are unifor...
• The change in free energy (∆G) during a
process is related to the change in enthalpy, or
change in total energy (∆H), ch...
Free Energy, Stability, and Equilibrium
• Free energy is a measure of a system’s
instability, its tendency to change to a ...
Figure 8.5
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy o...
Figure 8.5a
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy ...
Figure 8.5b
(a) Gravitational motion (b) Diffusion (c) Chemical reaction
Free Energy and Metabolism
• The concept of free energy can be applied to
the chemistry of life’s processes
© 2011 Pearson...
Exergonic and Endergonic Reactions in
Metabolism
• An exergonic reaction proceeds with a net
release of free energy and is...
Figure 8.6
(a) Exergonic reaction: energy released, spontaneous
(b) Endergonic reaction: energy required, nonspontaneous
R...
Figure 8.6a
(a) Exergonic reaction: energy released, spontaneous
Reactants
Energy
Products
Progress of the reaction
Amount...
Figure 8.6b
(b) Endergonic reaction: energy required, nonspontaneous
Reactants
Energy
Products
Amount of
energy
required
(...
Equilibrium and Metabolism
• Reactions in a closed system eventually reach
equilibrium and then do no work
• Cells are not...
Figure 8.7
(a) An isolated hydroelectric system
(b) An open hydro-
electric system
(c) A multistep open hydroelectric syst...
Figure 8.7a
(a) An isolated hydroelectric system
∆G < 0 ∆G = 0
Figure 8.7b
(b) An open hydroelectric
system
∆G < 0
Figure 8.7c
(c) A multistep open hydroelectric system
∆G < 0
∆G < 0
∆G < 0
Concept 8.3: ATP powers cellular work by
coupling exergonic reactions to endergonic
reactions
• A cell does three main kin...
The Structure and Hydrolysis of ATP
• ATP (adenosine triphosphate) is the cell’s
energy shuttle
• ATP is composed of ribos...
Figure 8.8
(a) The structure of ATP
Phosphate groups
Adenine
Ribose
Adenosine triphosphate (ATP)
Energy
Inorganic
phosphat...
Figure 8.8a
(a) The structure of ATP
Phosphate groups
Adenine
Ribose
Figure 8.8b
Adenosine triphosphate (ATP)
Energy
Inorganic
phosphate
Adenosine diphosphate (ADP)
(b) The hydrolysis of ATP
• The bonds between the phosphate groups
of ATP’s tail can be broken by hydrolysis
• Energy is released from ATP when the
...
How the Hydrolysis of ATP Performs Work
• The three types of cellular work (mechanical,
transport, and chemical) are power...
Figure 8.9
Glutamic
acid
Ammonia Glutamine
(b)Conversion
reaction
coupled
with ATP
hydrolysis
Glutamic acid
conversion
to ...
• ATP drives endergonic reactions by
phosphorylation, transferring a phosphate
group to some other molecule, such as a
rea...
Figure 8.10
Transport protein Solute
ATP
P P i
P iADP
P iADPATP
ATP
Solute transported
Vesicle Cytoskeletal track
Motor pr...
The Regeneration of ATP
• ATP is a renewable resource that is
regenerated by addition of a phosphate
group to adenosine di...
Figure 8.11
Energy from
catabolism (exergonic,
energy-releasing
processes)
Energy for cellular
work (endergonic,
energy-co...
Concept 8.4: Enzymes speed up metabolic
reactions by lowering energy barriers
• A catalyst is a chemical agent that speeds...
Figure 8.UN02
Sucrase
Sucrose
(C12H22O11)
Glucose
(C6H12O6)
Fructose
(C6H12O6)
The Activation Energy Barrier
• Every chemical reaction between molecules
involves bond breaking and bond forming
• The in...
Figure 8.12
Transition state
Reactants
Products
Progress of the reaction
Freeenergy
EA
∆G < O
A B
C D
A B
C D
A B
C D
How Enzymes Lower the EA Barrier
• Enzymes catalyze reactions by lowering the EA
barrier
• Enzymes do not affect the chang...
Figure 8.13
Course of
reaction
without
enzyme
EA
without
enzyme
EA with
enzyme
is lower
Course of
reaction
with enzyme
Rea...
Substrate Specificity of Enzymes
• The reactant that an enzyme acts on is called the
enzyme’s substrate
• The enzyme binds...
Figure 8.14
Substrate
Active site
Enzyme Enzyme-substrate
complex
(a) (b)
Catalysis in the Enzyme’s Active Site
• In an enzymatic reaction, the substrate binds to
the active site of the enzyme
• T...
Figure 8.15-1
Substrates
Substrates enter active site.
Enzyme-substrate
complex
Substrates are held
in active site by weak...
Figure 8.15-2
Substrates
Substrates enter active site.
Enzyme-substrate
complex
Substrates are held
in active site by weak...
Figure 8.15-3
Substrates
Substrates enter active site.
Enzyme-substrate
complex
Enzyme
Products
Substrates are held
in act...
Effects of Local Conditions on Enzyme
Activity
• An enzyme’s activity can be affected by
– General environmental factors, ...
Effects of Temperature and pH
• Each enzyme has an optimal temperature in
which it can function
• Each enzyme has an optim...
Figure 8.16
Optimal temperature for
typical human enzyme (37°C)
Optimal temperature for
enzyme of thermophilic
(heat-toler...
Figure 8.16a
Optimal temperature for
typical human enzyme (37°C)
Optimal temperature for
enzyme of thermophilic
(heat-tole...
Figure 8.16b
Rateofreaction
0 1 2 3 4 5 6 7 8 9 10
pH
(b) Optimal pH for two enzymes
Optimal pH for pepsin
(stomach
enzyme...
Cofactors
• Cofactors are nonprotein enzyme helpers
• Cofactors may be inorganic (such as a metal in
ionic form) or organi...
Enzyme Inhibitors
• Competitive inhibitors bind to the active site
of an enzyme, competing with the substrate
• Noncompeti...
Figure 8.17
(a) Normal binding (b) Competitive inhibition (c) Noncompetitive
inhibition
Substrate
Active
site
Enzyme
Compe...
The Evolution of Enzymes
• Enzymes are proteins encoded by genes
• Changes (mutations) in genes lead to changes
in amino a...
Figure 8.18
Two changed amino acids were
found near the active site.
Active site
Two changed amino acids
were found in the...
Concept 8.5: Regulation of enzyme activity
helps control metabolism
• Chemical chaos would result if a cell’s
metabolic pa...
Allosteric Regulation of Enzymes
• Allosteric regulation may either inhibit or
stimulate an enzyme’s activity
• Allosteric...
Allosteric Activation and Inhibition
• Most allosterically regulated enzymes are
made from polypeptide subunits
• Each enz...
Figure 8.19
Regulatory
site (one
of four)
(a) Allosteric activators and inhibitors
Allosteric enzyme
with four subunits
Ac...
Figure 8.19a
Regulatory site
(one of four)
(a) Allosteric activators and inhibitors
Allosteric enzyme
with four subunits
A...
Figure 8.19b
Inactive form
Substrate
Stabilized active
form
(b) Cooperativity: another type of allosteric activation
• Cooperativity is a form of allosteric regulation
that can amplify enzyme activity
• One substrate molecule primes an enz...
Identification of Allosteric Regulators
• Allosteric regulators are attractive drug
candidates for enzyme regulation becau...
Figure 8.20
Caspase 1 Active
site
Substrate
SH SH
SH
Known active form Active form can
bind substrate
Allosteric
binding s...
Figure 8.20a
Caspase 1 Active
site
Substrate
SH SH
SH
Known active form Active form can
bind substrate
Allosteric
binding ...
Figure 8.20b
Caspase 1
Active form Allosterically
inhibited form
Inhibitor
Inactive form
RESULTS
Feedback Inhibition
• In feedback inhibition, the end product of a
metabolic pathway shuts down the pathway
• Feedback inh...
Figure 8.21
Active site
available
Isoleucine
used up by
cell
Feedback
inhibition
Active site of
enzyme 1 is
no longer able...
Specific Localization of Enzymes Within
the Cell
• Structures within the cell help bring order to
metabolic pathways
• Som...
Figure 8.22
Mitochondria
The matrix contains
enzymes in solution that
are involved in one stage
of cellular respiration.
E...
Figure 8.22a
1 µm
Figure 8.UN03
Course of
reaction
without
enzyme
EA
without
enzyme EA with
enzyme
is lower
Course of
reaction
with enzyme
R...
Figure 8.UN04
Figure 8.UN05
Figure 8.UN06
Figure 8.UN07
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Ch 8: Introduction to Metabolism

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Ch 8: Introduction to Metabolism

  1. 1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick An Introduction to Metabolism Chapter 8
  2. 2. Overview: The Energy of Life • The living cell is a miniature chemical factory where thousands of reactions occur • The cell extracts energy and applies energy to perform work • Some organisms even convert energy to light, as in bioluminescence © 2011 Pearson Education, Inc.
  3. 3. Figure 8.1
  4. 4. 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 interactions between molecules within the cell © 2011 Pearson Education, Inc.
  5. 5. 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 © 2011 Pearson Education, Inc.
  6. 6. Figure 8.UN01 Enzyme 1 Enzyme 2 Enzyme 3 Reaction 1 Reaction 2 Reaction 3 ProductStarting molecule A B C D
  7. 7. • 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 © 2011 Pearson Education, Inc.
  8. 8. • 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 organisms manage their energy resources © 2011 Pearson Education, Inc.
  9. 9. Forms of Energy • Energy is the capacity to cause change • Energy exists in various forms, some of which can perform work © 2011 Pearson Education, Inc.
  10. 10. • 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 © 2011 Pearson Education, Inc. Animation: Energy Concepts
  11. 11. Figure 8.2 A diver has more potential energy on the platform than in the water. Diving converts potential energy to 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.
  12. 12. The Laws of Energy Transformation • Thermodynamics is the study of energy transformations • A isolated system, such as that approximated by liquid in a thermos, is isolated from its surroundings • In an open system, energy and matter can be transferred between the system and its surroundings • Organisms are open systems © 2011 Pearson Education, Inc.
  13. 13. 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 © 2011 Pearson Education, Inc.
  14. 14. 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 © 2011 Pearson Education, Inc.
  15. 15. Figure 8.3 (a) First law of thermodynamics (b) Second law of thermodynamics Chemical energy Heat
  16. 16. Figure 8.3a (a) First law of thermodynamics Chemical energy
  17. 17. Figure 8.3b (b) Second law of thermodynamics Heat
  18. 18. • 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 © 2011 Pearson Education, Inc.
  19. 19. 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 © 2011 Pearson Education, Inc.
  20. 20. Figure 8.4
  21. 21. Figure 8.4a
  22. 22. Figure 8.4b
  23. 23. • 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 © 2011 Pearson Education, Inc.
  24. 24. 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 © 2011 Pearson Education, Inc.
  25. 25. 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 © 2011 Pearson Education, Inc.
  26. 26. • 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 (T) ∆G = ∆H – T∆S • Only processes with a negative ∆G are spontaneous • Spontaneous processes can be harnessed to perform work © 2011 Pearson Education, Inc.
  27. 27. 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 © 2011 Pearson Education, Inc.
  28. 28. 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 • Less free energy (lower G) • More stable • Less work capacity (a) Gravitational motion (b) Diffusion (c) Chemical reaction
  29. 29. 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 • Less free energy (lower G) • More stable • Less work capacity
  30. 30. Figure 8.5b (a) Gravitational motion (b) Diffusion (c) Chemical reaction
  31. 31. Free Energy and Metabolism • The concept of free energy can be applied to the chemistry of life’s processes © 2011 Pearson Education, Inc.
  32. 32. 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 © 2011 Pearson Education, Inc.
  33. 33. Figure 8.6 (a) Exergonic reaction: energy released, spontaneous (b) Endergonic reaction: energy required, nonspontaneous Reactants Energy Products Progress of the reaction Amount of energy released (∆G < 0) Reactants Energy Products Amount of energy required (∆G > 0) Progress of the reaction FreeenergyFreeenergy
  34. 34. Figure 8.6a (a) Exergonic reaction: energy released, spontaneous Reactants Energy Products Progress of the reaction Amount of energy released (∆G < 0) Freeenergy
  35. 35. Figure 8.6b (b) Endergonic reaction: energy required, nonspontaneous Reactants Energy Products Amount of energy required (∆G > 0) Progress of the reaction Freeenergy
  36. 36. Equilibrium and Metabolism • Reactions in a closed system eventually reach equilibrium and then do no work • 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 • Closed and open hydroelectric systems can serve as analogies © 2011 Pearson Education, Inc.
  37. 37. Figure 8.7 (a) An isolated hydroelectric system (b) An open hydro- electric system (c) A multistep open hydroelectric system ∆G < 0 ∆G < 0 ∆G < 0 ∆G < 0 ∆G < 0 ∆G = 0
  38. 38. Figure 8.7a (a) An isolated hydroelectric system ∆G < 0 ∆G = 0
  39. 39. Figure 8.7b (b) An open hydroelectric system ∆G < 0
  40. 40. Figure 8.7c (c) A multistep open hydroelectric system ∆G < 0 ∆G < 0 ∆G < 0
  41. 41. 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 © 2011 Pearson Education, Inc.
  42. 42. 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 © 2011 Pearson Education, Inc.
  43. 43. Figure 8.8 (a) The structure of ATP Phosphate groups Adenine Ribose Adenosine triphosphate (ATP) Energy Inorganic phosphate Adenosine diphosphate (ADP) (b) The hydrolysis of ATP
  44. 44. Figure 8.8a (a) The structure of ATP Phosphate groups Adenine Ribose
  45. 45. Figure 8.8b Adenosine triphosphate (ATP) Energy Inorganic phosphate Adenosine diphosphate (ADP) (b) The hydrolysis of ATP
  46. 46. • 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 © 2011 Pearson Education, Inc.
  47. 47. 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 © 2011 Pearson Education, Inc.
  48. 48. Figure 8.9 Glutamic acid Ammonia Glutamine (b)Conversion reaction coupled with ATP hydrolysis Glutamic acid conversion to glutamine (a) (c) Free-energy change for coupled reaction Glutamic acid GlutaminePhosphorylated intermediate Glu NH3 NH2 Glu ∆GGlu = +3.4 kcal/mol ATP ADP ADP NH3 Glu Glu P P i P iADP Glu NH2 ∆GGlu = +3.4 kcal/mol Glu Glu NH3 NH2 ATP ∆GATP = −7.3 kcal/mol ∆GGlu = +3.4 kcal/mol + ∆GATP = −7.3 kcal/mol Net ∆G = −3.9 kcal/mol 1 2
  49. 49. • 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 © 2011 Pearson Education, Inc.
  50. 50. Figure 8.10 Transport protein Solute ATP P P i P iADP P iADPATP ATP Solute transported Vesicle Cytoskeletal track Motor protein Protein and vesicle moved (b) Mechanical work: ATP binds noncovalently to motor proteins and then is hydrolyzed. (a) Transport work: ATP phosphorylates transport proteins.
  51. 51. 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 © 2011 Pearson Education, Inc.
  52. 52. Figure 8.11 Energy from catabolism (exergonic, energy-releasing processes) Energy for cellular work (endergonic, energy-consuming processes) ATP ADP P i H2O
  53. 53. 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 © 2011 Pearson Education, Inc.
  54. 54. Figure 8.UN02 Sucrase Sucrose (C12H22O11) Glucose (C6H12O6) Fructose (C6H12O6)
  55. 55. 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 © 2011 Pearson Education, Inc.
  56. 56. Figure 8.12 Transition state Reactants Products Progress of the reaction Freeenergy EA ∆G < O A B C D A B C D A B C D
  57. 57. How Enzymes Lower the EA Barrier • 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 © 2011 Pearson Education, Inc. Animation: How Enzymes Work
  58. 58. Figure 8.13 Course of reaction without enzyme EA without enzyme EA with enzyme is lower Course of reaction with enzyme Reactants Products ∆G is unaffected by enzyme Progress of the reaction Freeenergy
  59. 59. 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 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 © 2011 Pearson Education, Inc.
  60. 60. Figure 8.14 Substrate Active site Enzyme Enzyme-substrate complex (a) (b)
  61. 61. 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 © 2011 Pearson Education, Inc.
  62. 62. Figure 8.15-1 Substrates Substrates enter active site. Enzyme-substrate complex Substrates are held in active site by weak interactions. 1 2 Enzyme Active site
  63. 63. Figure 8.15-2 Substrates Substrates enter active site. Enzyme-substrate complex Substrates are held in active site by weak interactions. Active site can lower EA and speed up a reaction. 1 2 3 Substrates are converted to products. 4 Enzyme Active site
  64. 64. Figure 8.15-3 Substrates Substrates enter active site. Enzyme-substrate complex Enzyme Products Substrates are held in active site by weak interactions. Active site can lower EA and speed up a reaction. Active site is available for two new substrate molecules. Products are released. Substrates are converted to products. 1 2 3 45 6
  65. 65. 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 © 2011 Pearson Education, Inc.
  66. 66. 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 © 2011 Pearson Education, Inc.
  67. 67. Figure 8.16 Optimal temperature for typical human enzyme (37°C) Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77°C) Temperature (°C) (a) Optimal temperature for two enzymes RateofreactionRateofreaction 120100806040200 0 1 2 3 4 5 6 7 8 9 10 pH (b) Optimal pH for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme)
  68. 68. Figure 8.16a Optimal temperature for typical human enzyme (37°C) Optimal temperature for enzyme of thermophilic (heat-tolerant) bacteria (77°C) Temperature (°C) (a) Optimal temperature for two enzymes Rateofreaction 120100806040200
  69. 69. Figure 8.16b Rateofreaction 0 1 2 3 4 5 6 7 8 9 10 pH (b) Optimal pH for two enzymes Optimal pH for pepsin (stomach enzyme) Optimal pH for trypsin (intestinal enzyme)
  70. 70. 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 © 2011 Pearson Education, Inc.
  71. 71. 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 © 2011 Pearson Education, Inc.
  72. 72. Figure 8.17 (a) Normal binding (b) Competitive inhibition (c) Noncompetitive inhibition Substrate Active site Enzyme Competitive inhibitor Noncompetitive inhibitor
  73. 73. 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 alter their substrate specificity • Under new environmental conditions a novel form of an enzyme might be favored © 2011 Pearson Education, Inc.
  74. 74. Figure 8.18 Two changed amino acids were found near the active site. Active site Two changed amino acids were found in the active site. Two changed amino acids were found on the surface.
  75. 75. 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 © 2011 Pearson Education, Inc.
  76. 76. 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 © 2011 Pearson Education, Inc.
  77. 77. 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 © 2011 Pearson Education, Inc.
  78. 78. Figure 8.19 Regulatory site (one of four) (a) Allosteric activators and inhibitors Allosteric enzyme with four subunits Active site (one of four) Active form Activator Stabilized active form Oscillation Non- functional active site Inactive form Inhibitor Stabilized inactive form Inactive form Substrate Stabilized active form (b) Cooperativity: another type of allosteric activation
  79. 79. Figure 8.19a Regulatory site (one of four) (a) Allosteric activators and inhibitors Allosteric enzyme with four subunits Active site (one of four) Active form Activator Stabilized active form Oscillation Nonfunctional active site Inactive form Inhibitor Stabilized inactive form
  80. 80. Figure 8.19b Inactive form Substrate Stabilized active form (b) Cooperativity: another type of allosteric activation
  81. 81. • 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 © 2011 Pearson Education, Inc.
  82. 82. Identification of Allosteric Regulators • Allosteric regulators are attractive drug candidates for enzyme regulation because of their specificity • Inhibition of proteolytic enzymes called caspases may help management of inappropriate inflammatory responses © 2011 Pearson Education, Inc.
  83. 83. Figure 8.20 Caspase 1 Active site Substrate SH SH SH Known active form Active form can bind substrate Allosteric binding site Allosteric inhibitor Hypothesis: allosteric inhibitor locks enzyme in inactive form Caspase 1 Active form Allosterically inhibited form Inhibitor Inactive form EXPERIMENT RESULTS Known inactive form
  84. 84. Figure 8.20a Caspase 1 Active site Substrate SH SH SH Known active form Active form can bind substrate Allosteric binding site Allosteric inhibitor Hypothesis: allosteric inhibitor locks enzyme in inactive form EXPERIMENT Known inactive form
  85. 85. Figure 8.20b Caspase 1 Active form Allosterically inhibited form Inhibitor Inactive form RESULTS
  86. 86. 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 © 2011 Pearson Education, Inc.
  87. 87. Figure 8.21 Active site available Isoleucine used up by cell Feedback inhibition Active site of enzyme 1 is no longer able to catalyze the conversion of threonine to intermediate A; pathway is switched off. Isoleucine binds to allosteric site. Initial substrate (threonine) Threonine in active site Enzyme 1 (threonine deaminase) Intermediate A Intermediate B Intermediate C Intermediate D Enzyme 2 Enzyme 3 Enzyme 4 Enzyme 5 End product (isoleucine)
  88. 88. Specific 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 © 2011 Pearson Education, Inc.
  89. 89. Figure 8.22 Mitochondria The matrix contains enzymes in solution that are involved in one stage of cellular respiration. Enzymes for another stage of cellular respiration are embedded in the inner membrane. 1 µm
  90. 90. Figure 8.22a 1 µm
  91. 91. Figure 8.UN03 Course of reaction without enzyme EA without enzyme EA with enzyme is lower Course of reaction with enzyme Reactants Products ∆G is unaffected by enzyme Progress of the reaction Freeenergy
  92. 92. Figure 8.UN04
  93. 93. Figure 8.UN05
  94. 94. Figure 8.UN06
  95. 95. Figure 8.UN07

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