Biology, Seventh Edition
Solomon • Berg • Martin
Chapter 6
Energy and
Metabolism
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Energy
• Capacity to do work, which is any
change in the state or motion of
matter
• Measured as heat energy
• Unit of measure is the kilocalorie
(kcal)
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Potential energy
• Capacity to do work owing to position
or state
• Chemical energy is potential energy
stored in chemical bonds
• Kinetic energy
• Energy of motion
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Closed system does not
exchange energy with its
surroundings
• Organisms are open systems
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
Closed
and
open
systems
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• First law of Thermodynamics
• Energy cannot be created or
destroyed
• Energy can be transferred and
changed in form
• Organisms cannot produce
energy, but as open systems,
they can capture it
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Second law of Thermodynamics
• Entropy is continuously increasing
• No energy transfer is 100% efficient
• Some energy is dissipated as heat
• Organisms maintain their
organization only with input of
energy from surroundings
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Metabolism
• Sum of all the chemical activities
taking place in an organism
• Anabolism
–Complex molecules synthesized from
simpler substances
• Catabolism
–Larger molecules broken down into
smaller ones
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Enthalpy is total potential energy
of a system
• As entropy increases, amount of
free energy decreases
• H = G + TS
–H is enthalpy
–G is free energy
–S is entropy
–T is absolute temperature in degrees Kelvin
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Exergonic reaction
• Releases energy that can perform
work
• In coupled reaction, supplies input of
free energy to drive an endergonic
reaction
• Endergonic reaction increases
free energy
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
Exergonic and endergonic reactions
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Dynamic equilibrium
• In a chemical reaction, rate of change
in one direction is the same as in the
opposite direction
• When concentration of reactant
molecules increases, the
reaction shifts until equilibrium is
re-established
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Adenosine triphosphate (ATP)
• Holds readily available energy for very
short periods
• Donates energy by means of terminal
phosphate group
• Common link between
–Exergonic and endergonic reactions
–Catabolism and anabolism
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
ATP and ADP
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
ATP links
exergonic
and
endergonic
reactions
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Redox reactions
• Substance that becomes oxidized
gives up energy
• Substance that becomes reduced
receives energy
• Essential part of cellular respiration,
photosynthesis, and other chemical
reactions
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
NAD
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Enzymes
• Biological catalysts
• Cells regulate the rate of chemical
reactions with enzymes
• Lower activation energy (energy
required to break existing bonds)
• Although most enzymes are proteins,
some types of RNA molecules have
catalytic activity as well
Copyright © 2005 Brooks/Cole — Thomson Learning
Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Enzymes
• Work best at specific temperature and
pH conditions
• Catalyze virtually every chemical
reaction that takes place in an
organism
• Some enzymes consist only of protein
• Some enzymes have two components
–Protein called apoenzyme
–Cofactor
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
Important classes of
enzymes
[insert table 6-1 when
available]
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Feedback inhibition
• Formation of an end product inhibits
an earlier reaction in the metabolic
pathway
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
Feedback
inhibition
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
• Reversible inhibition
• Competitive inhibition
–Inhibitor competes for the substrate for
the active site
• Noncompetitive inhibition
–Inhibitor binds with enzyme at a site other
than active site
• Irreversible inhibition
–Inhibitor combines with an enzyme and
permanently inactivates it
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Biology, Seventh Edition
CHAPTER 6 Energy and Metabolism
Competitive and noncompetitive inhibition
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