Life, 6th Edition

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CHAPTER 6Energy, Enzymes, and Metabolism
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Chapter 6 Energy, Enzymes, and Metabolism

• Energy and Energy Conversions
• ATP Transferring Energy in Cells
• Enzymes Biological Catalysts

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Chapter 6 Energy, Enzymes, and Metabolism

• Molecular Structure Determines Enzyme Function
• Metabolism and the Regulation of Enzymes

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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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Energy and Energy Conversions

• Potential energy can be converted to kinetic
  energy, which does work.
• Review Figure 6.1
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6.1
figure 06-01.jpg

• Figure 6.1

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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
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6.3
figure 06-03.jpg

• Figure 6.3

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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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6.4
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• Figure 6.4

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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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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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6.5
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• Figure 6.5

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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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6.6
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• Figure 6.6

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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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6.8
figure 06-08.jpg

• Figure 6.8

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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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6.9
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• Figure 6.9

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6.10
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• Figure 6.10

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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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6.11
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• Figure 6.11

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6.12
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• Figure 6.12

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Enzymes Biological Catalysts

• Enzymes are biological catalysts, highly specific
  for their substrates.
• Substrates bind to the active site, where
  catalysis takes place, forming an
  enzymesubstrate complex.
• Review Figure 6.13
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6.13
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• Figure 6.13

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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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6.14
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• Figure 6.14

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6.15
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• Figure 6.15

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Enzymes Biological Catalysts

• Substrate concentration affects the rate of an
  enzyme-catalyzed reaction.
• Review Figure 6.16
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6.16
figure 06-16.jpg

• Figure 6.16

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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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6.18
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• Figure 6.18

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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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Table 6.1
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• Table 6.1

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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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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 enzymes
  normal substrate may inhibit enzyme action.
• Review Figures 6.20, 6.21
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6.20
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• Figure 6.20

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6.21 Part 1
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• Figure 6.21 Part 1

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6.21 Part 2
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• Figure 6.21 Part 2

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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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6.22
figure 06-22.jpg

• Figure 6.22

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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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6.23
figure 06-23.jpg

• Figure 6.23

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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
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6.24
figure 06-24.jpg

• Figure 6.24

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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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6.25
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• Figure 6.25

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6.26
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• Figure 6.26