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Chapter 8 - Metabolism
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CHAPTER 8
Introduction to Metabolism
Campbell Reece Biology 7th Edition pp. 141-158
Concept 8.1
Organization of the Chemistry of Life into Metabolic Pathways
Complexity of Metabolism
The Laws of Energy Transformation
Concept 8.2
d
Exergonic and Endergonic Reactions in Metabolism
An exergonic reaction
Proceeds with a net release of free energy and is spontaneous
The greater the decrease in free energy the greater the amount of work that can be done.
E.g. overall cellular respiration reactions
Concept 8.3
The Structure and Hydrolysis of ATP
Energy is released from hydrolysis of ATP
When the terminal phosphate bond is broken
An exergonic reaction
delta G is about -13 kcal/mol (cellular conditions) -7.3 kcal/mol standard conditions
CHAPTER 8
Introduction to Metabolism
Campbell Reece Biology 7th Edition pp. 141-158
Role of ATP
Role of ATP hydrolysis
Can be coupled to endergonic reactions by transferring the phosphate group to another molecule
Drives endergonic reactions
Overall coupled reactions are exergonic
E.g. Glutamine synthesis
The Regeneration of ATP
Catabolic pathways
Drive the regeneration of ATP from ADP and phosphate
Concept 8.4 Rate of Metabolic Reactions
The effect of enzymes on reaction rate
reduce amount of absorbed heat required to reach transition state
Substrate Specificity of Enzymes
The catalytic cycle of an enzyme
What affects the activity of enzyme-catalyzed reactions
Effects of Temperature
Effects of pH
Cofactors
Enzyme Inhibitors
Competitive inhibitors
Bind to the active site of an enzyme, competing with the substrate and blocks substrate binding
Can be out-competed
Concept 8.5
They change shape when regulatory molecules bind to specific sites, affecting function
Feedback inhibition
Localization of Enzymes Within the Cell
Click to edit Master title style
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Second level
Third level
Fourth level
Fifth level
Click to edit Master text styles
Second level
Third level
Fourth level
Fifth level
Enzyme 1
Enzyme 2
Enzyme 3
Reaction 1
Reaction 2
Reaction 3
Starting molecule
Product
Fig. 8.5
Figure 8.6
Reactants
Products
Energy
Progress of the reaction
Free energy
(a) Exergonic reaction energy released
D G
Figure 8.6
Energy
Products
Reactants
Progress of the reaction
Free energy
(b) Endergonic reaction energy required
Figure 8.8
CH2
OH
OH
H
N
H
H
HC
NH2
Adenine
Ribose
Phosphate groups
O
CH
Figure 8.9
Adenosine triphosphate (ATP)
H2O
Energy
Inorganic phosphate
Adenosine diphosphate (ADP)
P i
hydrolysis of ATP releases a large amount of free energy EXERGONIC
2. ATP can be hydrolyzed
ATP H2O ADP Pi free energy
HPO42-
very stable
ATP - 2 unique features
(c) Chemical work ATP phosphorylates key reactants
Membrane
protein
Motor protein
P i
Protein moved
(a) Mechanical work ATP phosphorylates motor proteins
ATP
(b) Transport work ATP phosphorylates transport proteins
Solute
P i
transported
Solute
Glu
Glu
NH3
NH2
P i
P i
Reactants Glutamic acid
and ammonia
Product (glutamine)
made
ADP
Figure 8.11
ATP synthesis from
ADP P i requires energy
ATP
ADP P i
Energy for cellular work
(endergonic, energy-
consuming processes)
Energy from catabolism
(exergonic, energy yielding
processes)
ATP hydrolysis to
ADP P i yields energy
Figure 8.12
Figure 8.13
H2O
HO
OH
OH
OH
CH2OH
CH2OH
OH
CH2OH
Sucrase
HO
HO
OH
OH
CH2OH
CH2OH
CH2OH
Sucrose
Glucose
Fructose
C12H22O11
C6H12O6
C6H12O6
OH
Progress of the reaction
Products
Course of
reaction
without
enzyme
Reactants
Course of
reaction
with enzyme
EA
without
enzyme
EA with
enzyme
is lower
G
Free energy
Figure 8.15
Figure 8.16
Enzyme-substrate complex
Substrate
Substrates
Products
Enzyme
Enzyme-substrate
complex
Figure 8.17
Enzymes are unaffected by the reaction (reusable )
How do they lower EA
Act as a template for substrate orientation
Stress substrates and stabilize the transition state
Provides a favorable microenvironment
Induced fit
H-bonds, ionic bonds etc stabilize substrate
Active site available
Most metabolic reactions are reversible
What influences reaction directions or velocity
Each enzyme also has an optimal pH
between pH 6 - 8 for most enzymes.
Are exceptions
Pepsin vs Trypsin (pH 2 and pH 8 respectively)
Optimal temperature and pH favor the most active conformation of protein molecule
Figure 8.19
A competitive
inhibitor mimics the
substrate, competing
for the active site.
(b) Competitive inhibition
Competitive
inhibitor
A substrate can
bind normally to the
active site of an
enzyme.
Substrate
Active site
Enzyme
(a) Normal binding
Bind to enzyme and inhibit its activity
May be reversible or irreversible
if irreversible - usually due to covalent bond between inhibitor and enzyme
Figure 8.19
Noncompetitive inhibitor
(c) Noncompetitive inhibition
Binding is away from active site,
alters conformation of enzyme
active site no longer functions.
Substrate
Active site
Enzyme
(a) Normal binding
Stabilized inactive form
Allosteric activator stabilizes
active from of all subunits
Allosteric enyzme with four subunits
Active site (one of four)
Regulatory site (one of four)
Active form
Activator
Stabilized active form
Allosteric inhibitor stabilizes
inactive form of all subunits
Inhibitor
Inactive form
Non- functional active site
Figure 8.20 Allosteric activators and inhibitors.
Oscillation
Figure 8.20
Inactive form
Stabilized active form
substrate
Active site available
Isoleucine used up by cell
Feedback inhibition
Isoleucine binds to allosteric site
Initial substrate (threonine)
Enzyme 1 (threonine deaminase)
Intermediate A
Intermediate B
Intermediate C
Intermediate D
Enzyme 2
Enzyme 3
Enzyme 4
Enzyme 5
End product (isoleucine)
Figure 8.21
1 m
Mitochondria,
sites of cellular respiration
Figure 8.22
Increased localized concentration
Organisms live at the expense of free energy
During a spontaneous change
Free energy decreases and the stability of a system increases
Organisms live at the expense of free energy
During a spontaneous change
Free energy decreases and the stability of a system increases
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