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Summary Notes – BY1 1
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• The protein nature of enzymes
• Active sites interpreted in terms of 3 dimensional structure
Teacher guidance notes: (from1
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The general characteristics of enzymes are due to their biochemical nature as globular
proteins, showing specificity, requiring certain conditions and with a mode of action
lowering the activation energy of a reaction
2
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Enzymes:
• In cells metabolic reactions take place quickly & 1000s of reactions are taking place
simultaneously
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This complex 3-D shape gives the enzyme many of its properties:
• The enzyme is large
Ø Active site: is small and the functional part of the enzyme
Substrate: the molecule that the enzyme acts on
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Catalyst: a molecule that speeds up a chemical reaction, but remains unchanged at the end of
the reaction
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(II)

When the reaction is complete
Ø More products are released
Ø Leaving the enzyme unchanged
Ø & ready to receive another substrate molecule
Properties of enzymes:

Each enzyme will act only on 1 type of
substrate

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Metabolism: all the chemical processes that take place in a living organism
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Other enzymes catalyse reactions where small molecules are built into larger
molecules
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The enzyme is specific for that
particular substrate
Have a high turnover rate
I
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the enzymes convert many
molecules of substrate per unit time
E
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catalase
Activation energy: the energy
required to initiate a chemical
reaction
Is the energy needed to break
existing chemical bonds inside a
molecule

One way of making chemicals react together is to increase the energy in the form of
heat
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For a reaction to occur the reactants must collide with sufficient energy to alter the
arrangement of atoms in the molecule
Ø i
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an initial boost of energy is needed
Ø activation energy
Ø must be overcome
Ø before a reaction can proceed
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Enzymes:
• Are inactive at 0°C
• If the temperature increases then they become active again
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Enzymes become denatured at temperatures >40°C

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By lowering the activation energy enzymes decrease the input of energy required to
allow reactions to take place at the lower temperatures found in cells

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