Enzymes
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What’s the missing link?
What is the link between digestion, photosynthesis,
respiration and DNA replication?
They all depend on enzymes.
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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.
Cells create enzymes
based on instructions
carried in the cell’s genes.
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What are enzymes made of?
Enzymes are protein molecules, and so are made up of
amino acids. Most enzymes contain between 100 and
1,000 amino acids.
These amino acids
are joined together
in a long chain,
which is folded to
produce a unique
3D structure.
Different types of enzymes have different shapes and
functions because the sequence and type of amino
acids in their structure is different.
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Enzymes: true or false?
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Fussy enzymes?
Why are enzymes so specific in their reactions?
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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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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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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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Temperature and reaction rate
As the temperature increases, there are more collisions
between enzymes and reactants. This increases the rate
of reaction.
At a certain point, the temperature gets too high and the
enzymes are denatured. The enzymes can no longer bind
with reactants.
We can work out the Q10 for any reaction over a 10°C
interval with the following formula:
Q10 =
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rate at higher temperature
rate at lower temperature
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Enzyme inhibitors
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Identifying enzyme terms
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Glossary
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Anagrams
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Name the structure
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Multiple-choice quiz
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