Chapter 6: Energy, Enzymes, and Metabolism
CHAPTER 6
Energy, Enzymes, and
Metabolism
Chapter 6: Energy, Enzymes, and Metabolism
Chapter 6: Energy, Enzymes,
and Metabolism
Energy and Energy Conversions
ATP: Transferring Energy in Cells
Enzymes: Biological Catalysts
Chapter 6: Energy, Enzymes, and Metabolism
Chapter 6: Energy, Enzymes,
and Metabolism
Molecular Structure Determines Enzyme
Function
Metabolism and the Regulation of Enzymes
Chapter 6: Energy, Enzymes, and Metabolism
Energy and Energy Conversions
• Energy is the capacity to do work.
• Potential energy is the energy of state or
position; it includes energy stored in
chemical bonds.
• Kinetic energy is the energy of motion.
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Chapter 6: Energy, Enzymes, and Metabolism
Energy and Energy Conversions
• Potential energy can be converted to kinetic
energy, which does work.
Review Figure 6.1
5
Chapter 6: Energy, Enzymes, and Metabolism
6.1
Figure 6.1
figure 06-01.jpg
Chapter 6: Energy, Enzymes, and Metabolism
Energy and Energy Conversions
• The first law of thermodynamics tells us
energy cannot be created or destroyed.
• The second tells us that, in a closed system,
the quantity of energy available to do work
decreases and unusable energy increases.
Review Figure 6.3
7
Chapter 6: Energy, Enzymes, and Metabolism
6.3
Figure 6.3
figure 06-03.jpg
Chapter 6: Energy, Enzymes, and Metabolism
Energy and Energy Conversions
• Living things obey the laws of
thermodynamics.
• Organisms are open systems that are part
of a larger closed system.
Review Figure 6.4
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Chapter 6: Energy, Enzymes, and Metabolism
6.4
Figure 6.4
figure 06-04.jpg
Chapter 6: Energy, Enzymes, and Metabolism
Energy and Energy Conversions
• Changes in free energy, total energy,
temperature, and entropy are related by the
equation DG = DH – TDS.
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Chapter 6: Energy, Enzymes, and Metabolism
Energy and Energy Conversions
• Spontaneous, exergonic reactions release
free energy and have a negative DG.
• Non-spontaneous, endergonic reactions take
up free energy, have a positive DG, and
proceed only if free energy is provided.
Review Figure 6.5
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Chapter 6: Energy, Enzymes, and Metabolism
6.5
Figure 6.5
figure 06-05.jpg
Chapter 6: Energy, Enzymes, and Metabolism
Energy and Energy Conversions
• The change in free energy of a reaction
determines its point of chemical equilibrium,
at which forward and reverse reactions
proceed at the same rate.
• For spontaneous, exergonic reactions, the
equilibrium point lies toward completion.
Review Figure 6.6
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Chapter 6: Energy, Enzymes, and Metabolism
6.6
Figure 6.6
figure 06-06.jpg
Chapter 6: Energy, Enzymes, and Metabolism
ATP: Transferring Energy in
Cells
• ATP serves as an energy currency in cells.
• Hydrolysis of ATP releases a relatively large
amount of free energy.
Review Figure 6.8
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Chapter 6: Energy, Enzymes, and Metabolism
6.8
Figure 6.8
figure 06-08.jpg
Chapter 6: Energy, Enzymes, and Metabolism
ATP: Transferring Energy in
Cells
• The ATP cycle couples exergonic and
endergonic reactions, transferring free
energy from the exergonic to the
endergonic reaction.
Review Figures 6.9, 6.10
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Chapter 6: Energy, Enzymes, and Metabolism
6.9
Figure 6.9
figure 06-09.jpg
Chapter 6: Energy, Enzymes, and Metabolism
6.10
Figure 6.10
figure 06-10.jpg
Chapter 6: Energy, Enzymes, and Metabolism
Enzymes: Biological Catalysts
• The rate of a chemical reaction is
independent of DG but is determined by the
size of the activation energy barrier.
• Catalysts speed reactions by lowering the
barrier.
Review Figures 6.11, 6.12
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Chapter 6: Energy, Enzymes, and Metabolism
6.11
Figure 6.11
figure 06-11.jpg
Chapter 6: Energy, Enzymes, and Metabolism
figure 06-12.jpg
6.12
Figure 6.12
Chapter 6: Energy, Enzymes, and Metabolism
Enzymes: Biological Catalysts
• Enzymes are biological catalysts, highly
specific for their substrates.
• Substrates bind to the active site, where
catalysis takes place, forming an enzyme–
substrate complex.
Review Figure 6.13
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-13.jpg
6.13
Figure 6.13
Chapter 6: Energy, Enzymes, and Metabolism
Enzymes: Biological Catalysts
• At the active site, a substrate can be
oriented correctly, chemically modified, or
strained.
• As a result, the substrate readily forms its
transition state, and the reaction proceeds.
Review Figures 6.14, 6.15
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-14.jpg
6.14
Figure 6.14
Chapter 6: Energy, Enzymes, and Metabolism
figure 06-15.jpg
6.15
Figure 6.15
Chapter 6: Energy, Enzymes, and Metabolism
Enzymes: Biological Catalysts
• Substrate concentration affects the rate of
an enzyme-catalyzed reaction.
Review Figure 6.16
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-16.jpg
6.16
Figure 6.16
Chapter 6: Energy, Enzymes, and Metabolism
Molecular Structure Determines
Enzyme Function
• The active site where substrate binds
determines the specificity of an enzyme.
• Upon binding to substrate, some enzymes
change shape, facilitating catalysis.
Review Figures 6.13, 6.18
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-18.jpg
6.18
Figure 6.18
Chapter 6: Energy, Enzymes, and Metabolism
Molecular Structure Determines
Enzyme Function
• Some enzymes require cofactors for catalysis.
• Prosthetic groups are permanently bound to the
enzyme.
• Coenzymes usually are not.
• They enter into the reaction as a “cosubstrate,” as
they are changed by the reaction and released from
the enzyme.
Review Table 6.1
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Chapter 6: Energy, Enzymes, and Metabolism
Table 6.1
Table 6.1
table 06-01.jpg
Chapter 6: Energy, Enzymes, and Metabolism
Metabolism and the Regulation
of Enzymes
• Metabolism is organized into pathways: the
product of one reaction is a reactant for the
next.
• Each reaction is catalyzed by an enzyme.
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Chapter 6: Energy, Enzymes, and Metabolism
Metabolism and the Regulation
of Enzymes
• Enzyme activity is subject to regulation.
• Some compounds react irreversibly with them and
reduce their catalytic activity.
• Others react reversibly, inhibiting enzyme action
temporarily.
• A compound structurally similar to an enzyme’s
normal substrate may inhibit enzyme action.
Review Figures 6.20, 6.21
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-20.jpg
6.20
Figure 6.20
Chapter 6: Energy, Enzymes, and Metabolism
6.21 – Part 1
Figure 6.21 – Part 1
figure 06-21a.jpg
Chapter 6: Energy, Enzymes, and Metabolism
6.21 – Part 2
Figure 6.21 – Part 2
figure 06-21b.jpg
Chapter 6: Energy, Enzymes, and Metabolism
Metabolism and the Regulation
of Enzymes
• For allosteric enzymes, plots of reaction rate
versus substrate concentration are
sigmoidal, in contrast to plots of the same
variables for non-allosteric enzymes.
Review Figure 6.22
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-22.jpg
6.22
Figure 6.22
Chapter 6: Energy, Enzymes, and Metabolism
Metabolism and the Regulation
of Enzymes
• Allosteric inhibitors bind to a site different
from the active site and stabilize the inactive
form of the enzyme.
• The multiple catalytic subunits of many
allosteric enzymes interact cooperatively.
Review Figure 6.23
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-23.jpg
6.23
Figure 6.23
Chapter 6: Energy, Enzymes, and Metabolism
Metabolism and the Regulation
of Enzymes
• The end product of a metabolic pathway
may inhibit the allosteric enzyme that
catalyzes the commitment step of the
pathway.
Review Figure 6.24
44
Chapter 6: Energy, Enzymes, and Metabolism
figure 06-24.jpg
6.24
Figure 6.24
Chapter 6: Energy, Enzymes, and Metabolism
Metabolism and the Regulation
of Enzymes
• Enzymes are sensitive to their environment.
• Both pH and temperature affect enzyme
activity.
Review Figures 6.25, 6.26
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Chapter 6: Energy, Enzymes, and Metabolism
figure 06-25.jpg
6.25
Figure 6.25
Chapter 6: Energy, Enzymes, and Metabolism
figure 06-26.jpg
6.26
Figure 6.26