Enzymes:
The Biological Catalysts
Energy of Activation
• Most reactions do not start spontaneously
• They require energy, such as a spark, to get started.
• This is called activation energy
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Energy of Activation
• The energy used
to break the
bonds in the
reactants so they
can be reformed
in the products is
called the energy
of activation.
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Enzymes
• Enzymes are biological catalysts that increase
the reaction rate of biochemical reactions.
Characteristics of
enzymes
A. Made of proteins (or
RNA).
B.They are very specific
and only work with a
certain set of reactants
or substrates that fit on
The enzyme shown is lysozyme
their active site.
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Induced Fit
C. Enzymes can be used over and over again.
D. When an enzyme binds with the substrate, the
bonded substrate interacts with the enzyme
causing it to change shape. This change in
shape facilitates the chemical reaction to occur.
This is called the induced fit.
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Enzyme Example Ribonuclease
• Ribonuclease
decomposes RNA,
and the nucleotides
can be recycled.
• The purple part is the
enzyme; the green
part is the substrate
(RNA).
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Enzymes Work by Lowering the Energy
of Activation
E. Enzymes increase the reaction rate by
lowering the energy of activation.
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The Enzyme Sucrase Decomposing
Sucrose
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Initial Velocity
• The reaction rate of an enzymatic reaction is always
fastest at the beginning because plenty of substrate
is available.
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Effects on Reaction Rates
Temperature increases enzyme action until the
enzyme protein is denatured
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Effect on Reaction Rates
Most enzymes work best with a pH of 7, but
some can work in other ranges before denaturing
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Effect onReaction Rates
Competitive Inhibitors block enzyme activity by
mimicking the substrate
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Effect of Noncompetitive Inhibitors and
Enzymatic Reaction Rates
Noncompetitve inhibitors block enzyme function
too, but attach a different point than the active site
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Draw and Label Activation Energy
Diagram
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Reactions to Know
• Hydrolysis Rxn – breaks apart a compound by
adding a water molecule
• Dehydration Synthesis Rxn – links two compouunds
by creating and releasing a water molecule
• Endergonic Rxn – a reaction that requires
energy
• Exergonic Rxn – a reaction that releases
energy
• Redox Rxn – a reaction that involves
transferring electrons
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