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Slide 2

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An enzyme is a biological catalyst.
Enzymes can be intracellular or extracellular (they act
inside cells or outside cells)
Enzymes are globular proteins. They are coiled in a
precise 3D shape (their tertiary structure)
They possess an active site: a region to which specific
molecules can bind.
This molecule is the substrate of the enzyme. The shape
of the active site allows the substrate to fit perfectly,
and to be held in place by temporary bonds that form
between the substrate and the R groups of the enzyme's
amino acids.
This combined structure is called the enzyme-substrate
complex.…read more

Slide 3

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Each type of enzyme will usually act on 1 type of
substrate molecule.
The shape of the active site will only allow one shape of
molecule to fit, like a lock and key.
When the substrate fits into the active site, the enzyme
changes slightly to accommodate it. This is called
induced fit.
The enzyme must be a perfect match. The enzyme is
said to be specific for the substrate.
The enzyme may split up substrate molecules or join
them together (e.g linking amino acids to form
When the reaction is complete, the product(s) leave the
active site, and the enzyme remains unchanged by the
process, and available to receive another substrate
molecule.…read more

Slide 4

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How an enzyme catalyses the breakdown of a substrate
molecule.…read more

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Enzymes increase the rate at which chemical reactions occur.
In many reactions, the substrate will not be converted to a product
unless it is temporarily given some extra energy.
This energy is called the activation energy.
Enzymes catalyse reactions by lowering the activation energy.
Left: Illustration of activation energy…read more

Slide 6

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When a substrate binds with an
enzyme, the shape of its
molecule is slightly changed.
This makes it easier for the
substrate to change into a
product; the activation energy is
lower.…read more


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