1. An Introduction to Metabolism
Chapter 6
An Introduction to Metabolism p

2. Concept 6.1: An organism’s metabolism transforms matter and energy
Metabolism is…
Metabolism is an emergent property of life that arises from interactions between molecules within the cell
A metabolic pathway begins with a specific molecule and ends with a product, and each step is catalyzed by a specific enzyme
© 2014 Pearson Education, Inc. 2

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. Catabolism
Anabolism

5. Forms of Energy Energy Kinetic energy Thermal energy Heat
Potential energy
Chemical energy 5

6. 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. 6

7. The Laws of Energy Transformation
Thermodynamics=
Isolated System
Open System 7

8. 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
Figure 6.3a The two laws of thermodynamics (part 1: conservation of energy)
Chemical
energy
(a) First law of thermodynamics 8

9. According to the second law of thermodynamics:
Every energy transfer or transformation increases the entropy of the universe
Heat
Figure 6.3b The two laws of thermodynamics (part 2: entropy)
(b) Second law of thermodynamics 9

10. 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
How does energy flow into an ecosystem?
How does it flow out?
© 2014 Pearson Education, Inc. 10

11. Concept 6.2: The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously
A living system’s free energy (G) is energy that can do work when temperature and pressure are uniform
What is ΔG?
© 2014 Pearson Education, Inc. 11

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
Exergonic Reactions
Endergonic Reactions
© 2014 Pearson Education, Inc. 13

14. Amount of energy released (G  0) Amount of energy required (G  0)
Figure 6.6
(a) Exergonic reaction: energy released, spontaneous
Reactants
Amount of
energy
released
(G  0)
Energy
Free energy
Products
Progress of the reaction
(b) Endergonic reaction: energy required,
nonspontaneous
Products
Figure 6.6 Free energy changes (ΔG) in exergonic and endergonic reactions
Amount of
energy
required
(G  0)
Energy
Free energy
Reactants
Progress of the reaction 14

15. (a) An isolated hydroelectric system
Figure 6.7
G  0
G  0
(a) An isolated hydroelectric system
(b) An open
hydroelectric
system
G  0
Figure 6.7 Equilibrium and work in isolated and open systems
G  0
G  0
G  0
(c) A multistep open hydroelectric system 15

16. Concept 6.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions
A cell does three main kinds of work
Chemical
Transport
Mechanical
Cells utilize energy coupling
© 2014 Pearson Education, Inc. 16

17. The Structure and Hydrolysis of ATP
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)
Figure 6.8
(b) The hydrolysis of ATP 17

18. Figure 6.9: How ATP drives chemical work!
GGlu  3.4 kcal/mol
Glutamic acid
Ammonia
Glutamine
(a) Glutamic acid conversion to glutamine
Glutamic acid
Phosphorylated
intermediate
Glutamine
(b) Conversion reaction coupled with ATP hydrolysis
GGlu  3.4 kcal/mol
Figure 6.9 How ATP drives chemical work: energy coupling using ATP hydrolysis
GGlu  3.4 kcal/mol
GATP  −7.3 kcal/mol
GATP  −7.3 kcal/mol 
(c) Free-energy change for coupled reaction
G  −3.9 kcal/mol
Net 18

19. Figure 6.10 How ATP drives transport and mechanical work
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. 19

20. The Regeneration of ATP
Energy from
catabolism
(exergonic, energy-
releasing processes)
Energy for cellular
work (endergonic,
energy-consuming
processes)
Figure 6.11 The ATP cycle
Figure 6.11 20

21. Concept 6.4: Enzymes speed up metabolic reactions by lowering energy barriers
Sucrase
Sucrose
(C12H22O11)
Glucose
(C6H12O6)
Fructose
(C6H12O6)
Figure 6.UN02 In-text figure, hydrolysis of sucrose, p. 125
Figure 6.UN02 21

22. Figure 6.12: An energy profile of an exergonic reactionB 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 22

23. Figure 6.13: The effect of an enzyme on activation energy
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 23

24. Figure 6.14: Induced fit between an enzyme and its substrate
Active site
Figure 6.14 Induced fit between an enzyme and its substrate
Enzyme
Enzyme-substrate
complex 24

25. 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 25

26. Effects of Local Conditions on Enzyme Activity
An enzyme’s activity can be affected by:
© 2014 Pearson Education, Inc. 26

27. Figure 6.16: Factors that affect enzyme activity
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 27

28. Cofactors and Enzyme Inhibitors
What are Cofactors?
What are enzyme inhibitors?
Two types
© 2014 Pearson Education, Inc. 28

29. Figure 6.17 Inhibition of Enzyme Activity
(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. Concept 6.5: Regulation of enzyme activity helps control metabolism
Chemical chaos would result if a cell’s metabolic pathways were not tightly regulated
How does a cell regulate its pathways?
© 2014 Pearson Education, Inc. 30

31. (a) Allosteric activators and inhibitors
Figure 6.18a
(a) Allosteric activators and inhibitors
Allosteric enzyme
with four subunits
Active site
(one of four)
Regulatory
site (one
of four)
Activator
Active form
Stabilized
active form
Oscillation
Figure 6.18a Allosteric regulation of enzyme activity (part 1: activation and inhibition)
Non-
functional
active site
Inhibitor
Inactive
form
Stabilized
inactive form 31

32. Stabilized active form
Figure 6.18b
(b) Cooperativity: another type of allosteric
activation
Substrate
Figure 6.18b Allosteric regulation of enzyme activity (part 2: cooperativity)
Inactive form
Stabilized
active form 32

33. Feedback Inhibition
In feedback inhibition, the end product of a metabolic pathway shuts down the pathway
WHY is it important?
© 2014 Pearson Education, Inc. 33

34. Figure 6.19 Feedback Inhibition
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) 34

35. Mitochondria The matrix contains enzymes in solution
Figure 6.20
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.
Figure 6.20 Organelles and structural order in metabolism
1 m 35