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Enzymes are ORGANIC CATALYSTS!
Enzymes are proteins (made up of amino acids)
Enzymes function by lowering the activation
energy of reactions.
Enzymes can act rapidly and can cause chemicals
to act 107 times faster than without the enzyme
present.
There are over 2000 known enzymes, each of
which is involved with one specific chemical
reaction.
All chemical
reactions
require
activation
energy to
break
chemical
bonds and
begin the
reaction.
Enzymes lower the barriers that normally prevent chemical reactions
from occurring (or slow them down) by decreasing the required
activation energy. Thus, in the presence of enzymes, reactions proceed
and/or proceed at a faster rate.
Generally speaking, these are the terms to be familiar with
Substrate
Enzyme
Active Site
Products
An enzyme has a Specific Binding Site
for a specific substrate to bind
Enzymes are substrate
specific.
i.e. The enzyme peptidase
(which breaks bonds in
proteins) will not work on
starch (which is broken down
by amylase in the mouth)
When the substrate and enzyme bind it forms a
Lock and Key Model
Only the correctly sized key (substrate) fits into
the key hole (active site) of the lock (enzyme).
Induced Fit
Model

The active site of the unbound
enzyme is not the exact
complement of the shape of
the substrate.

However, the enzyme does
bind to the substrate.

After binding of the enzyme
to the substrate is initiated, a
conformational change in the
shape of the active site which
results in a new shape of the
active site that is
complementary to the shape
of the substrate.
Here’s an example of an enzyme that bonds with the sucrose
(SUBSTRATE)
Once water is added and the bond breaks in the sucrose molecule
and a glucose and fructose molecule are released (PRODUCTS)
Maltase
1 Maltose + Enzyme  2 Glucose + Enzyme
Reactant
Product
Competitive
Non-competitive
Factors that affect the reaction
 Temperature
• Increases in temperature will speed up
the rate of the reaction
• When heated too much, enzymes will
become denatured (lose their shape)
 pH
• Changes in pH will also denature the
enzyme by changing the shape of the
enzyme
• Enzymes are also adapted to operate at
a specific pH or pH range
Examples of enzymes:
• Ligase
• Isomerase
• Transferase
• Cellulase
• Lactase
• Pectinase
• Maltase
• Catalase
• Carbonic anhydrase
• Peroxidase
• Peptidase
• Sucrase
•Salivary amylase
• Oxidase
You may have heard of people who are lactose intolerant,
or you may suffer from this problem yourself. The
problem arises because the sugar in milk – lactose – does
not get broken down into its glucose components.
Therefore, it cannot be digested.
The intestinal cells of lactose-intolerant people do not
produce lactase, the enzyme needed to break down lactose.
This problem shows how the lack of just one enzyme in
the human body can lead to problems.
A person who is lactose intolerant can swallow a drop of
lactase prior to drinking milk and the problem is solved.
Many enzyme deficiencies are not so easy to fix!
Other world applications:
• Some liver diseases = result from lack of enzymes
• Tay-Sachs disease = lack an enzyme necessary for breaking
down certain fatty substances in brain and nerve cells
• Fabry Disease = A chemical in the body which would
normally be broken down builds up and causes damage, mainly
to the heart, kidneys and brain
•Lysosomal Storage Disorder (i.e Gaucher Disease: an
enzyme is missing in cells in the bones, bone marrow, liver and
spleen. There is an accumulation of waste in these tissues in the
body and they become enlarged)
•Glycogen storage disease (i.e. Pompe disease) = missing
enzyme that is needed to break down glycogen, a stored form of
sugar used for energy