BIOLOGY
Chapter 6: pp. 103-116
10th Edition
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solar
energy
Insert figure 6.1 here
heat
heat
Chemical
energy
Sylvia S. Mader
Metabolism: Energy
and Enzymes
heat
Mechanical energy
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display
1
Outline

Forms of Energy


Metabolic Reactions


Laws of Thermodynamics
ATP
Metabolic Pathways

Energy of Activation

Enzymes

Photosynthesis

Cellular Respiration
2
Forms of Energy


Kinetic:

Energy of motion

Mechanical
Potential:

Stored energy

Chemical
3
Flow of Energy
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solar
energy
heat
heat
heat
Chemical
energy
Mechanical energy
4
Laws of Thermodynamics


First law:

Law of conservation of energy

Energy cannot be created or destroyed, but

Energy CAN be changed from one form to another
Second law:

Law of entropy

When energy is changed from one form to another,
there is a loss of usable energy

Waste energy goes to increase disorder
5
Carbohydrate Metabolism
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heat
carbohydrate
muscle contraction
6
Cells and Energy
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H2 O
energy
C H O
6 12 6
CO2
Glucose
Carbon dioxide and water
• more organized
• more potential energy
• less stable (entropy)
• less organized
• less potential energy
• more stable (entropy)
a.
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
energy
H+
H+
H+
channel protein
H+
H+
H+
H+
H+
Unequal distribution
Equal distribution
of hydrogen ions
of hydrogen ions
• more organized
• more potential energy
• less stable (entropy)
• less organized
• less potential energy
• more stable (entropy)
b.
7
Metabolic Reactions and Energy
Transformations


Metabolism:

Sum of cellular chemical reactions in cell

Reactants participate in reaction

Products form as result of reaction
Free energy is the amount of energy available to
perform work

Exergonic Reactions - Products have less free energy
than reactants

Endergonic Reactions - Products have more free
energy than reactants
8
ATP and Coupled Reactions

Adenosine triphosphate (ATP)



Composed of:



High energy compound used to drive metabolic
reactions
Constantly being generated from adenosine
diphosphate (ADP)
Adenine and ribose (together = adenosine), and
Three phosphate groups
Coupled reactions


Energy released by an exergonic reaction
captured in ATP
That ATP used to drive an endergonic reaction
9
The ATP Cycle
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adenosine triphosphate
P
Energy from
exergonic reactions
(e.g., cellular
respiration)
P
ATP
ADP
+
Energy for endergonic
reactions (e.g., protein
synthesis, nerve
conduction, muscle
contraction)
P
P
adenosine diphosphate
a.
P
P
+
+
P
phosphate
b.
2.25
b: © Darwin Dale/Photo Researchers, Inc.
10
Coupled Reactions
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1 Myosin head assumes
its resting shape when
it combines with ATP.
2 As ATP is split into
ADP and p myosin
head attaches to actin
3. Myosin head pulls
on actin as ADP
and p are released
actin
myosin
ATP
P
ADP
11
Metabolic Reactions and Energy
Transformations


Metabolism:

Sum of cellular chemical reactions in cell

Reactants participate in reaction

Products form as result of reaction
Free energy is the amount of energy available to
perform work

Exergonic Reactions - Products have less free energy
than reactants

Endergonic Reactions - Products have more free
energy than reactants
12
Work-Related Functions of ATP

Primarily to perform cellular work

Chemical Work - Energy needed to synthesize
macromolecules

Transport Work - Energy needed to pump
substances across plasma membrane

Mechanical Work - Energy needed to contract
muscles, beat flagella, etc
13
Metabolic Pathways

Reactions are usually occur in a sequence

Products of an earlier reaction become reactants of a
later reaction

Such linked reactions form a metabolic pathway

Begins with a particular reactant,

Proceeds through several intermediates, and

Terminates with a particular end product
AB C D E FG
“A” is Initial
Reactant
B, C, D, E, and F
are Intermediates
“G” is End
Product
14
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15
Enzymes

Enzymes

Protein molecules that function as catalysts

The reactants of an enzymatically accelerated reaction
are called substrates

Each enzyme accelerates a specific reaction

Each reaction in a metabolic pathway requires a
unique and specific enzyme

End product will not appear unless ALL enzymes
present and functional
E1
E2
E3
E4
E5
E6
A B  C  D  E  F  G
16
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Enzymes: Energy of Activation


Reactants often “reluctant” to participate in
reaction

Energy must be added to at least one reactant to
initiate the reaction

Energy of activation
Enzyme Operation:

Enzymes operate by lowering the energy of activation

Accomplished by bringing the substrates into contact
with one another
18
Energy of Activation
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energy of
activation
(Ea)
energy of
reactant
Free Energy
energy of
activation
(Ea)
energy of
product
enzyme not present
enzyme present
Progress of the Reaction
19
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20
Enzyme-Substrate Complex

The active site complexes with the
substrates

Causes active site to change shape

Shape change forces substrates together,
initiating bond

Induced fit model
21
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Degradation vs. Synthesis


Degradation:

Enzyme complexes with a single substrate molecule

Substrate is broken apart into two product molecules
Synthesis:

Enzyme complexes with two substrate molecules

Substrates are joined together and released as single
product molecule
23
Degradation vs. Synthesis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
products
enzyme
substrate
enzyme-substrate
complex
active site
Degradation
The substrate is broken down
to smaller products.
enzyme
a.
product
enzyme
substrates
enzyme-substrate
complex
active site
b.
enzyme
Synthesis
The substrates are combined
to produce a larger product.
24
Factors Affecting Enzyme Activity

Substrate concentration



Temperature




Enzyme activity increases with substrate concentration
More collisions between substrate molecules and the
enzyme
Enzyme activity increases with temperature
Warmer temperatures cause more effective collisions
between enzyme and substrate
However, hot temperatures destroy enzyme
pH

Most enzymes are optimized for a particular pH
25
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26
Factors Affecting Enzyme Activity:
Temperature
Rate of Reaction
(product per unit of time)
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0
10
20
30
40
50
60
Temperature C
a. Rate of reaction as a function of
temperature
b. Body temperature of ectothermic animals
often limits rates of reactions.
c. Body temperature of endothermic animals
promotes rates of reactions.
b: © James Watt/Visuals Unlimited; c: © Creatas/PunchStock
27
Factors Affecting Enzyme Activity: pH
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
trypsin
Rate of Reaction
(product per unit of
time)
pepsin
0
1
2
3
4
5
6
7
8
9
10
11
12
pH
28
Factors Affecting Enzyme Activity

Cells can affect presence/absence of
enzyme

Cells can affect concentration of enzyme

Cells can activate or deactivate enzyme

Enzyme Cofactors

Molecules required to activate enzyme

Coenzymes are organic cofactors, like some vitamins

Phosphorylation – some require addition of a phosphate
29
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30
Factors Affecting Enzyme Activity

Reversible enzyme inhibition


When a substance known as an inhibitor binds
to an enzyme and decreases its activity

Competitive inhibition – substrate and the inhibitor
are both able to bind to active site

Noncompetitive inhibition – the inhibitor binds not at
the active site, but at the allosteric site
Feedback inhibition – The end product of a
pathway inhibits the pathway’s first enzyme
31
Cofactor at Active Site
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cofactor
substrate
active site
a.
b.
32
Factors Affecting Enzyme Activity:
Feedback Inhibition
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A
E
enzymes
1
substrates A
1
allosteric site
1
E
B
E
2
C
3
E
4
D
E
5
E
F
(end
product)
Metabolic pathway produces F, the end product.
active site
2
E
E
F
(end
1 product)
F binds to allosteric site and the active site of E1 changes shape.
F
A
3
E
1
(end
product)
A cannot bind to E1; the enzyme has been inhibited by F.
33
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34
Irreversible Inhibition

Materials that irreversibly inhibit an enzyme are
known as poisons

Cyanides inhibit enzymes resulting in all ATP
production

Penicillin inhibits an enzyme unique to certain
bacteria

Heavy metals irreversibly bind with many
enzymes

Nerve gas irreversibly inhibits enzymes required
by nervous system
35
Oxidation-Reduction

Oxidation-reduction (redox) reactions:

Electrons pass from one molecule to another

The molecule that loses an electron is oxidized

The molecule that gains an electron is reduced

Both take place at same time

One molecule accepts the electron given up by
the other
36
Photosynthesis and Cellular Respiration
37
Electron Transport Chain

Membrane-bound carrier proteins found in
mitochondria and chloroplasts

Physically arranged in an ordered series

Starts with high-energy electrons and low-energy ADP

Pass electrons from one carrier to another

Electron energy used to pump hydrogen ions (H+) to one side
of membrane

Establishes electrical gradient across membrane


Electrical gradient used to make ATP from ADP –
Chemiosmosis
Ends with low-energy electrons and high-energy ATP
38
A Metaphor for the Electron
Transport Chain
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e
high-energy
electrons
energy for
synthesis of
ATP
electron
transport chain
e
low-energy
electrons
39
Chemiosmosis
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
High H + concentration
H + pump in electron
transport chain
H+
H+
H+
H+
H+
ADP +
P
ATP
synthase
complex
energy from
electron transfers
H+
H+
ATP
Low H + concentration
40
Review

Forms of Energy


Metabolic Reactions


Laws of Thermodynamics
ATP
Metabolic Pathways

Energy of Activation

Enzymes

Photosynthesis

Cellular Respiration
41
Chapter 6: pp. 103-116
Insert figure 6.1 here
PowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or display
10th Edition
Sylvia S. Mader
Metabolism: Energy
and Enzymes
BIOLOGY
42