1. An Introduction to Metabolism6
An Introduction to Metabolism

2. Figure 6.1
Figure 6.1 What causes these two squid to glow? 2

3. Concept 6.1: An organism’s metabolism transforms matter and energy
Metabolism - totality of an organism’s chemical reactions
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4. 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 4

5. Catabolic pathways release energy by breaking down complex molecules
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6. Anabolic pathways consume energy to build complex molecules from simpler ones
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7. 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. 7

8. (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 8

9. Figure 6.4
Figure 6.4 Order as a characteristic of life 9

10. Free-Energy Change (G), Stability, and Equilibrium
A living system’s free energy is energy that can do work when temperature and pressure are uniform
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11. ∆G = Gfinal state – Ginitial state
The change in free energy (∆G) is the difference between the free energy of the final state and the free energy of the initial state
∆G = Gfinal state – Ginitial state
Only processes with a negative ∆G are spontaneous
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12. 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 12

13. Exergonic and Endergonic Reactions in Metabolism
An exergonic reaction
net release of free energy
Spontaneous
∆G is negative
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14. 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 14

15. 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 15

16. An endergonic reaction absorbs free energy Nonspontaneous
∆G is positive
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17. The Structure and Hydrolysis of ATP
ATP (adenosine triphosphate)
composed of
ribose (sugar),
adenine (nitrogenous base)
three phosphate groups
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18. (a) The structure of ATP
Figure 6.8a
Adenine
Phosphate groups
Ribose
Figure 6.8a The structure and hydrolysis of adenosine triphosphate (ATP) (part 1: structure)
(a) The structure of ATP 18

19. Adenosine triphosphate (ATP)
Figure 6.8b
Adenosine triphosphate (ATP)
Figure 6.8b The structure and hydrolysis of adenosine triphosphate (ATP) (part 2: hydrolysis)
Energy
Inorganic
phosphate
Adenosine diphosphate (ADP)
(b) The hydrolysis of ATP 19

20. 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. 20

21. Concept 6.4: Enzymes speed up metabolic reactions by lowering energy barriers
An enzyme is a catalytic protein
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22. 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 22

23. 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 23

24. Activation Energy reactants
energy barrier with no enzyme to promote reaction
energy barrier with an enzyme’s participation
products
Fig. 6-9, p.96

25. How Enzymes Speed Up Reactions
Enzymes catalyze reactions by lowering the activation energy (EA) barrier
Enzymes do not affect the change in free energy (∆G); instead, they hasten reactions that would occur eventually
Animation: How Enzymes Work
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26. 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 26

27. Substrate Specificity of Enzymes
The reactant that an enzyme acts on is called the substrate
enzyme-substrate complex enzyme bound to substrate
active site - region on enzyme where substrate binds
Enzyme specificity results from complementary fit between active site and substrate
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28. 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 28

29. Substrates are 2 Substrates enter 1 held in active site by
Figure 2
Substrates are
held in active site by
weak interactions. 1
Substrates enter
active site.
Substrates
Enzyme-substrate
complex
Figure The active site and catalytic cycle of an enzyme (steps 1-2) 29

30. Substrates are 2 Substrates enter 1 held in active site by
Figure 2
Substrates are
held in active site by
weak interactions. 1
Substrates enter
active site.
Substrates
Enzyme-substrate
complex
Figure The active site and catalytic cycle of an enzyme (step 3) 3
Substrates are
converted to
products. 30

31. 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
Figure The active site and catalytic cycle of an enzyme (step 4) 4
Products are
released. 3
Substrates are
converted to
products.
Products 31

32. 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 32

33. Effects of Local Conditions on Enzyme Activity
An enzyme’s activity can be affected by temperature, pH and Chemicals that influence the enzyme
Each enzyme has an optimal temperature & pH
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34. 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 34

35. Effect of Temperature
Fig. 6-13, p.81

36. Temperature Effects on Phenotype
This Rabbit is homozygous for allele producing heat-sensitive version of an enzyme in melanin-producing pathway
Melanin is produced in cooler areas of body
Figure Page 179

37. This Siamese cat, raised in a cold environment in Moscow in the late 20s, developed a relatively dark coat. An area on his shoulder was shaved, and the cat wore a warm jacket while the fur was growing back. When the shaved hair grew back in, it was white, the same color as the cat's belly, due to the increased temperature under the jacket. This was not due to scarring, as the hair grew in normally colored later.

39. Cofactors Cofactors are organic or inorganic nonprotein enzyme helpers
organic cofactors are called coenzymes
Some coenzymes are vitamins
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40. Enzyme Inhibitors
Competitive inhibitors bind to active site competing with substrate
Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape
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41. (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 41

42. Allosteric Regulation of Enzymes
Allosteric regulation - regulatory molecule binds to protein at one site and affects protein’s function at another site
may either inhibit or stimulate enzyme
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43. (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 43

44. Feedback Inhibition
In feedback inhibition, the end product of a metabolic pathway shuts down the pathway
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45. 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) 45