ACTIVITY #13: ENZYMES
VOCABULARY
Enzyme
Catalyst
Substrate
Activation energy
Active site
Denaturation
ENZYMES
Some chemical reactions would be too slow or
have too high of an activation energy without
a little help
Catalyst: a substance that speeds up a
chemical reaction
Works by lowering the activation energy
Cells make special proteins called enzymes to
act as catalysts for chemical reactions
One type of enzyme for each type of chemical
reaction
Its shape makes it specific for its job
ACTIVATION ENERGY
Would the hill be
higher or lower
with an enzyme
present?
Lower
HOW DO ENZYMES WORK?
1. Provide a site for the reactants to be brought
together to react
2. Help to break the bonds of the reactants
 Reduces the energy needed for the reaction
 “Enzyme Catalyzed Reaction”- a reaction
sped up by an enzyme
SUBSTRATE
Substrates- what the reactants are called
in an enzyme catalyzed reaction
Bind to a place on the enzyme called the
active site which has a specific shape
2 MODELS HELP EXPLAIN HOW ENZYMES
WORK
1. "Lock and Key Model": substrates fit the
active site of an enzyme like a key fits into a
lock

A very specific interaction!
 Provides the site for the reactants to come
together
Substrate
Enzyme
2. “Induced-fit Model”:
enzyme binds the
substrate(s) and
slightly changes its
shape to “hug” the
substrate(s) tightly
(like a handshake)

Places “strain” on
existing bonds,
allowing bonds to
break and the
chemical reaction to
go forward
Example of an enzyme-catalyzed
Carbonic Acid is formed
reaction: ____________
by combining
Carbon dioxide
___________________
and
water in the presence of the
enzyme
Carbonic anhydrase
“_______________________”.
WHY AREN’T ENZYMES CONSIDERED
A REACTANT OR A PRODUCT?
After the product is
released from the
enzyme, the enzyme
is recycled and used
again
Enzymes are
reusable!
COMMON HYDROLYTIC ENZYMES
( T H E SUF F I X " – A SE " C OM M ON LY I N DI CATES T H AT A P ROT E I N
I S A N E N Z Y ME)
1. protease- any enzyme that speeds hydrolysis
or breakdown of proteins
2. sucrase (a disaccharidease) - an enzyme
which speeds the breakdown of Sucrose
.
3. lipase - any enzyme which speeds the
Lipids
breakdown of
4. nuclease - any enzyme which speeds the
Nucleic acids
breakdown of
5. amylase - an enzyme which speeds the
breakdown of amylose (=starch!)
FACTORS AFFECTING ENZYME
ACTIVITY
Temperature, pH, and regulatory molecules
affect enzyme activity
 An increase in temperature will increase the rate of a
reaction to a certain point
 After that point, the enzyme will no longer work
DENATURATION
Denaturation - when a protein unfolds and
loses its overall shape (and thus function) due
to increased temp or changes in pH
 Denatured enzymes lose the shape of their active site
and will no longer function
Think!
Why are temperature and pH
important factors in
maintaining homeostasis?
If they are not maintained
then proteins, including
enzymes, would denature
and chemical reactions
could not occur!