Transcript Enzymes - Boardworks Education

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What are enzymes?
Enzymes are biological catalysts – they speed up the
chemical reactions that take place inside all cells, but
without being used up in the process.
There are many thousands of different types of enzyme,
and each one catalyzes a different reaction.
Enzymes occur naturally in all organisms, but they are
increasingly being used in industrial processes.
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Why do enzymes speed up reactions?
Enzymes speed up reactions by lowering the activation
energy (Ea) of a reaction. The activation energy is the
energy needed to start a reaction.
Different reactions have different activation energies.
energy (kJ)
Ea without enzyme
Ea with enzyme
reaction (time)
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Why is shape important?
The shape of an enzyme is very important because it has
a direct effect on how it catalyzes a reaction.
Why do enzymes have different
shapes?
An enzyme’s shape is
determined by the sequence of
amino acids in its structure, and
the bonds which form between
the atoms of those molecules.
Different types of enzymes have different shapes and
functions because the order and type of amino acids in
their structure is different.
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Why are enzymes so specific?
Enzymes are very specific about which reactions they
catalyze. Only molecules with exactly the right shape will
bind to the enzyme and react. These are the reactant, or
substrate, molecules.
The part of the enzyme to
which the reactant binds is
called the active site.
This is a very specific shape
and the most important part
of the enzyme.
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What happens at the active site?
In the same way that a key fits into a lock, so a substrate
is thought to fit into an enzyme’s active site. The enzyme
is the lock, and the reactant is the key.
↔
+
enzyme
+
reactant
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↔
↔
enzyme-reactant
complex
+
↔
enzyme
+
products
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The lock and key model
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Factors affecting enzymes
The rate of enzyme-catalyzed reactions depends on
several factors. What are some of these?
Factors that affect the rate of a reaction include:
 temperature
 substrate concentration
 pH
 surface area
 enzyme concentration
 pressure.
All enzymes work best at only one particular temperature
and pH: this is called the optimum.
Different enzymes have different optimum temperatures
and pH values.
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Factors affecting enzymes
If the temperature and pH changes sufficiently beyond an
enzyme’s optimum, the shape of the enzyme irreversibly
changes.
This affects the shape of the active site and means that
the enzyme will no longer work.
When this happens the enzyme is denatured.
heat
pH
normal
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denatured
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Enzymes and temperature
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Enzymes: true or false?
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