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Of all the functions of proteins, one of the most important
is that of catalysis
In the absence of catalysis, most reactions in biological systems
would take place far too slowly to provide products at an adequate
pace for metabolising organisms
The catalysts that serve this function in living organisms are
called ENZYMES
All enzymes are globular proteins and are the most efficient
catalysts known
Enzymes are able to increase the rate of reaction by a factor of
up to 1020 over uncatalysed reactions…read more

Slide 3

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Characteristics of Enzymes
· They are proteins of high Substrate
molecular weight molecule in
· They are biological the ACTIVE
catalysts SITE
· They are sensitive to
temperature changes being
denatured at high
temperatures
· They are sensitive to pH
· They are generally specific
in the reactions they
catalyse
· Enzymes possess an active
site within which chemical Enzyme molecule
reactions take place…read more

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The Active Site
Enzyme Active
molecule site
Substrate
molecules
Reaction (complementary
shape to active
occurs site)
Product
Enzyme remains molecules
diffuse away
unchanged from the
active site
Substrate molecules bind with enzyme molecules at the active
site as a consequence of their complementary shapes. This is the
basis of the LOCK AND KEY MODEL of enzyme activity…read more

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The Lock And Key Model
In an enzyme - catalysed reaction, the enzyme binds
to the substrate to form a complex
Enzyme S An enzyme - substrate complex
molecule forms
Products diffuse
away from the
active site
A reaction The lock & key model
occurs proposes that the substrate
forming an binds to the active site
enzyme - product
complex which it fits exactly, like a
key in a lock…read more

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The Induced Fit Model
This model takes into account the fact that proteins (enzymes)
have some three-dimensional flexibility
Substrate binds to the enzyme
at the active site
SUBSTRATE
Binding of the substrate
induces the enzyme to change
shape such that there is an
exact fit once the substrate
has bound
According to this model, reactions can
Enzyme Molecule only take place AFTER induced fit has
occurred…read more

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