1. An Introduction to Metabolism6
An Introduction to Metabolism

2. Concept 6.1: An organism’s metabolism transforms matter and energy
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3. Enzyme 1 Enzyme 2 Enzyme 3 Starting molecule A B C D Product
Figure 6.UN01
Enzyme 1
Enzyme 2
Enzyme 3
Starting
molecule A B C D
Product
Reaction 1
Reaction 2
Reaction 3
Figure 6.UN01 In-text figure, metabolic pathway schematic, p. 116 3

4. Catabolic pathways
Anabolic pathways
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5. A diver has more potential energy on the platform.
Figure 6.2
Diving converts
potential energy to
kinetic energy.
A diver has more potential
energy on the platform.
Figure 6.2 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. 5

6. (a) First law of thermodynamics (b) Second law of thermodynamics
Figure 6.3
Heat
Chemical
energy
Figure 6.3 The two laws of thermodynamics
(a) First law of thermodynamics
(b) Second law of thermodynamics 6

7. Free-Energy Change (G), Stability, and Equilibrium
A living system’s free energy
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8. The change in free energy (∆G) is the difference between
∆G = Gfinal state – Ginitial state
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9. More free energy (higher G) Less stable Greater work capacity
Figure 6.5
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 6.5 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 9

10. Exergonic and Endergonic Reactions in Metabolism
An exergonic reaction
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11. Amount of energy released (G  0)
Figure 6.6a
(a) Exergonic reaction: energy released, spontaneous
Reactants
Amount of
energy
released
(G  0)
Energy
Free energy
Products
Figure 6.6a Free energy changes (ΔG) in exergonic and endergonic reactions (part 1: exergonic)
Progress of the reaction 11

12. Amount of energy required (G  0)
Figure 6.6b
(b) Endergonic reaction: energy required,
nonspontaneous
Products
Amount of
energy
required
(G  0)
Energy
Free energy
Reactants
Figure 6.6b Free energy changes (ΔG) in exergonic and endergonic reactions (part 2: endergonic)
Progress of the reaction 12

13. An endergonic reaction
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14. The Structure and Hydrolysis of ATP
ATP (adenosine triphosphate)
composed of
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15. (a) The structure of ATP
Figure 6.8
Adenine
Phosphate groups
Ribose
(a) The structure of ATP
Adenosine triphosphate (ATP)
Figure 6.8 The structure and hydrolysis of adenosine triphosphate (ATP)
Energy
Inorganic
phosphate
Adenosine diphosphate (ADP)
(b) The hydrolysis of ATP 15

16. Protein and vesicle moved
Figure 6.10
Transport protein
Solute
Solute transported
(a) Transport work: ATP phosphorylates transport proteins.
Vesicle
Cytoskeletal track
Figure 6.10 How ATP drives transport and mechanical work
Motor protein
Protein and
vesicle moved
(b) Mechanical work: ATP binds noncovalently to motor proteins
and then is hydrolyzed. 16

17. Concept 6.4: Enzymes speed up metabolic reactions by lowering energy barriers
An enzyme
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18. Sucrose (C12H22O11) Glucose (C6H12O6) Fructose (C6H12O6)
Figure 6.UN02
Sucrase
Sucrose
(C12H22O11)
Glucose
(C6H12O6)
Fructose
(C6H12O6)
Figure 6.UN02 In-text figure, hydrolysis of sucrose, p. 125 18

19. Progress of the reaction
Figure 6.12 A B C D
Transition state A B EA
Free energy C D
Reactants A B
Figure 6.12 Energy profile of an exergonic reaction
G  0 C D
Products
Progress of the reaction 19

20. How Enzymes Speed Up Reactions
Enzymes do not affect the change in free energy (∆G);
Animation: How Enzymes Work
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21. Progress of the reaction
Figure 6.13
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 6.13 The effect of an enzyme on activation energy
Products
Progress of the reaction 21

22. Substrate Specificity of Enzymes
the substrate
enzyme-substrate complex
active site -
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23. Substrate Active site Enzyme Enzyme-substrate complex Figure 6.14
Figure 6.14 Induced fit between an enzyme and its substrate
Enzyme
Enzyme-substrate
complex 23

24. 2 Substrates are held in active site by weak interactions. 1
Figure 2
Substrates are
held in active site by
weak interactions. 1
Substrates enter
active site.
Substrates
Enzyme-substrate
complex
Active
site is
available
for new
substrates. 5
Figure The active site and catalytic cycle of an enzyme (step 5)
Enzyme
Products are
released. 4 3
Substrates are
converted to
products.
Products 24

25. Effects of Local Conditions on Enzyme Activity
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26. Optimal temperature for typical human enzyme (37C)
Figure 6.16
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 6.16 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 26

27. Cofactors Cofactors coenzymes Some coenzymes are vitamins 27
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28. Enzyme Inhibitors Competitive inhibitors Noncompetitive inhibitors 28
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29. (b) Competitive inhibition (c) Noncompetitive inhibition
Figure 6.17
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive
inhibition
Substrate
Active site
Competitive
inhibitor
Enzyme
Figure 6.17 Inhibition of enzyme activity
Noncompetitive
inhibitor 29

30. Allosteric Regulation of Enzymes
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31. (a) Allosteric activators and inhibitors
Figure 6.18
(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
Figure 6.18 Allosteric regulation of enzyme activity
Non-
functional
active site
Inhibitor
Inactive
form
Stabilized
inactive form 31

32. Feedback Inhibition In feedback inhibition, 32
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33. End product (isoleucine)
Figure 6.19
Active site available
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Isoleucine
used up by
cell
Intermediate A
Feedback
inhibition
Enzyme 2
Intermediate B
Enzyme 3
Intermediate C
Isoleucine
binds to
allosteric
site.
Figure 6.19 Feedback inhibition in isoleucine synthesis
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine) 33