1. Energy Transformations and Enzymes
AP Bio Chapter 6

2. The reactions of a cell either consume or release energy.
Metabolism – totality of an organism’s chemical processes
Controlled by enzymes – biological catalysts that lower energy barriers and speed up metabolic processes

3. Each step is catalyzed by a specific enzyme
A metabolic pathway begins with a specific molecule and ends with a product.
Each step is catalyzed by a specific enzyme
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4. Starting molecule Product
Fig. 8-UN1
Enzyme 1
Enzyme 2
Enzyme 3 A B C D
Reaction 1
Reaction 2
Reaction 3
Starting
molecule
Product

6. Types of pathways
Catabolic pathways – break down complex molecules; release energy
Anabolic pathways – require energy to combine simpler molecules to make complex ones; requires energy.
Bioenergetics – how organisms manage their energy resources

7. enerGy

8. Energy Potential – energy matter possesses
The capacity to cause change
Energy exists in various forms, some of which can perform work.
Kinetic – energy of motion
Potential – energy matter possesses
because of its location or structure

9. A diver has more potential energy on the platform than in the water.
Fig. 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.

10. In molecules, the Potential Energy is the energy stored in the bonds.

11. KE is also random movement of
atoms or molecules as in thermal energy (heat)

12. The Laws of Energy Transformation
Thermodynamics is the study of energy transformations
A closed 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
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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
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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
The quantity of energy is constant but not the quality!

15. Living cells unavoidably convert organized forms of energy to heat
Fig. 8-3
Living cells unavoidably convert organized forms of energy to heat
Heat
CO2 +
Chemical
energy
H2O
Figure 8.3 The two laws of thermodynamics
(a) First law of thermodynamics
(b) Second law of thermodynamics

16. Biological Order and Disorder
Cells create ordered structures from less ordered materials
Energy flows into an ecosystem in the form of light and exits in the form of heat.

17. 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
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18. LIFE REQUIRES FREE ENERGY!

19. 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.
The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously.
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20. Gibbs Free Energy ∆G = ∆H – T∆S
The change in free energy (∆G) during a process is related to the change in enthalpy, or (∆H), change in entropy (∆S), and temperature in Kelvin (T).

21. ΔH ENTHALPY – heat content of molecule (total PE in its bonds)
It is a measure of the total energy there
NegativeΔ H – releases heat; exothermic
Positive Δ H – absorbs heat; endothermic
Spontaneous reactions have - Δ H

22. Δ S ENTROPY (disorder) S final state – S initial state
Spontaneous reactions have + Δ S

23. Temp necessary due to more KE of molecules, disrupting order
T (temperature 0K)
Temp necessary due to more KE of molecules, disrupting order
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24. (a) Gravitational motion (b) Diffusion (c) Chemical reaction
Fig. 8-5b
Spontaneous
change
Spontaneous
change
Spontaneous
change
Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change
(a) Gravitational motion
(b) Diffusion
(c) Chemical reaction

25. In summary
∆G < 0, spontaneous, exergonic, net release of free energy
∆G > 0, endergonic, not spontaneous, absorbs free energy
∆G = 0, equilibrium (bad for cells)

26. 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!

27. Closed and open hydroelectric systems can serve as analogies
Fig. 8-7
∆G < 0
∆G = 0
A catabolic pathway in a cell releases free energy in a series of reactions
Closed and open hydroelectric systems can serve as analogies
(a) An isolated hydroelectric system
∆G < 0
(b) An open hydroelectric
system
Figure 8.7 Equilibrium and work in isolated and open systems
∆G < 0
∆G < 0
∆G < 0
(c) A multistep open hydroelectric system

28. Exergonic and Endergonic Reactions in Metabolism …one more time….
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
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29. Progress of the reaction
Fig. 8-6
Reactants
Amount of
energy
released
(∆G < 0)
Energy
Free energy
Products
Progress of the reaction
(a) Exergonic reaction: energy released
Products
Amount of
energy
required
(∆G > 0)
Figure 8.6 Free energy changes (ΔG) in exergonic and endergonic reactions
Energy
Free energy
Reactants
Progress of the reaction
(b) Endergonic reaction: energy required

30. Exergonic reaction

31. Endergonic reaction- energy absorbing

32. To provide energy for endergonic reactions, coupled reactions pair exergonic reactions with endergonic reactions

33. System with
High Free En.
Low Free En.
Stability
Spontaneous
Equilibrium
Work Capacity

34. System with
High Free En.
Low Free En.
Stability
low
high
Spontaneous
Equilibrium
Work Capacity

35. System with
High Free En.
Low Free En.
Stability
low
high
Spontaneous
Change will be
change will not be
Equilibrium
Work Capacity

36. System with
High Free En.
Low Free En.
Stability
low
high
Spontaneous
Change will be
change will not be
Equilibrium
moves toward
Is at
Work Capacity

37. System with
High Free En.
Low Free En.
Stability
low
high
Spontaneous
Change will be
change will not be
Equilibrium
moves toward
Is at
Work Capacity

38. How 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

39. Membrane protein Solute Solute transported Vesicle Cytoskeletal track
Fig. 8-11
Membrane protein P P i
Solute
Solute transported
(a) Transport work: ATP phosphorylates
transport proteins
ADP
ATP + P i
Vesicle
Cytoskeletal track
Figure 8.11 How ATP drives transport and mechanical work
ATP
Motor protein
Protein moved
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed

41. In cell, the source of energy for work is ATP.
ATP is a nucleoside triphosphate.
Nucleoside = adenosine
= adenine (purine) + ribose
3 Phosphate groups

42. Adenine Phosphate groups Ribose
Fig. 8-8
Adenine
Phosphate groups
Figure 8.8 The structure of adenosine triphosphate (ATP)
Ribose

43. Energy is released from ATP when the terminal phosphate bond is broken
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
For the Cell Biology Video Stick Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

44. H2O P P P Adenosine triphosphate (ATP) P + P P + Energy
Fig. 8-9 P P P
Adenosine triphosphate (ATP)
H2O
Figure 8.9 The hydrolysis of ATP P + P P +
Energy i
Inorganic phosphate
Adenosine diphosphate (ADP)

46. The Phosphate that is removed can be bonded to another molecule and make that molecule more reactive. That molecule is PHOSPHORYLATED.
This is a coupled reaction.

47. ATP = ADP + P + energy (-7kcal)
ATP = ADP + P + energy (-7kcal). Energy transfer occurs by a coupled reaction Example : Phosphocreatine stores high energy bonds in skeletal muscle
ATP = ADP + P + energy (-

48. How 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

49. ∆G = +3.4 kcal/mol Glutamic acid Ammonia Glutamine
Fig. 8-10
NH2
NH3 +
∆G = +3.4 kcal/mol
Glu
Glu
Glutamic
acid
Ammonia
Glutamine
(a) Endergonic reaction 1
ATP phosphorylates
glutamic acid,
making the amino
acid less stable. P +
ATP +
ADP
Glu
Glu
NH2 P 2
Ammonia displaces
the phosphate group,
forming glutamine.
NH3 + + P i
Glu
Glu
Figure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis
(b) Coupled with ATP hydrolysis, an exergonic reaction
(c) Overall free-energy change

50. Membrane protein Solute Solute transported Vesicle Cytoskeletal track
Fig. 8-11
Membrane protein P P i
Solute
Solute transported
(a) Transport work: ATP phosphorylates
transport proteins
ADP
ATP + P i
Vesicle
Cytoskeletal track
Figure 8.11 How ATP drives transport and mechanical work
ATP
Motor protein
Protein moved
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed

51. ADP can be regenerated.
By cellular respiration from the breakdown (catabolism) of food
By light in photosynthesis

52. + H2O Energy for cellular work (endergonic, energy-consuming
Fig. 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

53. Why do dinoflagellates glow?2 1

54. It is a chemical reaction involving, you got it……
ENZYMES

55. Enzyme-
Luciferase
Substrates-
luciferin and
oxygen
Product: oxyluciferin

56. Enzymes Speed up reactions Lower activation energy – EA
energy absorbed by reactants to reach
an unstable transition state (bonds
fragile); may be supplied by heat
Activation energy barrier – necessary to
keep energy-rich molecules from
decomposing spontaneously

57. Progress of the reaction
Fig. 8-14 A B C D
Transition state A B EA C D
Free energy
Reactants A B
Figure 8.14 Energy profile of an exergonic reaction
∆G < O C D
Products
Progress of the reaction

58. Progress of the reaction
Fig. 8-15
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 8.15 The effect of an enzyme on activation energy
Products
Progress of the reaction

59. Properties of enzymes Are proteins
Are specific for the substrate (what they work on) which is determined by 3-D shape. They bind at the active site. The substrate induces the enzyme to change shape. INDUCED FIT
May have “ase” name endings, may be named for substrate they work on

60. Or, it can go the other way, two substrates can be combined to make a product.

61. Enzymes can be used over and over! They are not changed in the reaction.

62. The active site can lower an EA barrier by
Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment
Covalently bonding to the substrate

63. Substrate Active site Enzyme Enzyme-substrate complex (a) (b)
Fig. 8-16
Substrate
Active site
Figure 8.16 Induced fit between an enzyme and its substrate
Enzyme
Enzyme-substrate
complex
(a)
(b)

64. Substrates enter active site; enzyme
Fig. 8-17
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
Active
site is
available
for two new
substrate
molecules. 6
Figure 8.17 The active site and catalytic cycle of an enzyme
Enzyme 5
Products are
released.
Substrates are
converted to
products. 4
Products

66. Ex:
Hydrolase – hydrolytic (catabolic)
Isomerase – rearrangment of atoms

67. Effects of Temperature and pH
Each enzyme has an
optimal temperature
optimal pH in which it can function
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68. Optimal temperature for typical human enzyme Optimal temperature for
Fig. 8-18
Optimal temperature for
typical human enzyme
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
bacteria
Rate of reaction 20 40 60 80
100
Temperature (ºC)
(a) Optimal temperature for two enzymes
Optimal pH for pepsin
(stomach enzyme)
Optimal pH
for trypsin
(intestinal
enzyme)
Figure 8.18 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

69. 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
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70. Noncompetitive inhibitor
Fig. 8-19
Substrate
Active site
Competitive
inhibitor
Enzyme
Figure 8.19 Inhibition of enzyme activity
Noncompetitive inhibitor
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive inhibition

71. Allosteric Regulation of Enzymes
Allosteric regulation can also activate 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
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73. Allosteric Activators And Inhibitors
Fig. 8-20
Allosteric enyzme
with four subunits
Active site
(one of four)
Allosteric
Activators
And
Inhibitors
Regulatory
site (one
of four)
Activator
Active form
Stabilized active form
Oscillation
Non-
functional
active
site
Inhibitor
Inactive form
Stabilized inactive
form
Figure 8.20 Allosteric regulation of enzyme activity
(a) Allosteric activators and inhibitors
Substrate
Inactive form
Stabilized active
form
(b) Cooperativity: another type of allosteric activation

74. Stabilized active form
Fig. 8-20a
Allosteric enzyme
with four subunits
Active site
(one of four)
Regulatory
site (one
of four)
Activator
Active form
Stabilized active form
Oscillation
Figure 8.20a Allosteric regulation of enzyme activity
Non-
functional
active
site
Inhibitor
Inactive form
Stabilized inactive
form
(a) Allosteric activators and inhibitors

75. Cooperativity is a form of allosteric regulation that can amplify enzyme activity
In cooperativity, binding by a substrate to one active site stabilizes favorable conformational changes at all other subunits
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76. (b) Cooperativity: another type of allosteric activation
Fig. 8-20b
Substrate
Inactive form
Stabilized active
form
Figure 8.20b Allosteric regulation of enzyme activity
(b) Cooperativity: another type of allosteric activation

77. Identification of Allosteric Regulators
Allosteric regulators are attractive drug candidates for enzyme regulation
Ex - Inhibition of proteolytic enzymes called caspases may help management of inappropriate inflammatory responses
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78. EXPERIMENT Allosteric binding site Allosteric inhibitor Caspase 1
Fig. 8-21a
EXPERIMENT
Caspase 1
Active
site
Substrate SH SH
Known active form
Active form can
bind substrate
Figure 8.21 Are there allosteric inhibitors of caspase enzymes?
Allosteric
binding site SH
S–S
Allosteric
inhibitor
Known inactive form
Hypothesis: allosteric
inhibitor locks enzyme
in inactive form

79. RESULTS Caspase 1 Inhibitor Active form Allosterically inhibited form
Fig. 8-21b
RESULTS
Caspase 1
Inhibitor
Figure 8.21 Are there allosteric inhibitors of caspase enzymes?
Active form
Allosterically
inhibited form
Inactive form

80. Cofactors and Coenzymes also help regulate enzyme action
Holoenzyme- An apoenzyme together with its cofactor. A holoenzyme is complete and catalytically active. Most cofactors are not covalently bound but instead are tightly bound.
An apoenzyme is an inactive enzyme, activation of the enzyme occurs upon binding of an organic or inorganic cofactor.
Both cofactors and coenzymes help to complete the structure of a conjugated enzyme, forming a holoenzyme.

82. Enzyme activity can be determined by
Amount of substrate – faster up to a limit when substrate gives out
Temperature – faster up to optimal temp, then slows. High temp may denature (unravel protein).
pH – most work at 6 – 8
Cofactors – small nonproteins that bind to the active site
- inorganic Zn, Cu, Co
Coenzymes organic molecules (vitamins)
Presence of inhibitors

83. 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
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84. Figure 8.22 Feedback inhibition in isoleucine synthesis Enzyme 4
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
Figure 8.22 Feedback inhibition in isoleucine synthesis
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine)

85. Specific Localization of Enzymes Within the Cell
Some enzymes act as structural components of membranes
In eukaryotic cells, some enzymes reside in specific organelles; for example, lysosomes
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86. Back to the dinoflagellates….enzymes are located in scintillons.