Enzymes
Characteristics of Enzymes
1. Proteins
1. Monomer is: _______ ______
2. Catalysts
a. Start or speed up chemical reactions without
being used up
In case you wondered…How
do enzymes work?
1. Lower Activation Energy to speed up
rates of reaction
a. Reactions require energy to
begin…enzymes lower the amount of energy
required.
Naming
1. Often end in “–ase”
2. Usually relates to the reaction they help
start
a. Examples: lactase, sucrase,
protease, carboxypeptidase
Catalyzing Process
1. A unique 3-D shape of an enzyme
determines which chemical reaction it
catalyzes
2. Important Vocab:
a. SUBSTRATE: A specific reactant that
an enzyme acts on is called a
substrate of the enzyme.
2. Important Vocab (cont.):
b. ACTIVE SITE: A substrate fits into a
region of the enzyme called an active
site.
1. An active site is typically a pocket or
groove on the surface of the enzyme.
3. The enzyme and substrate form a
complex
substrate
Active site
enzyme
Enzyme-substrate complex
Lock and Key Model
P
+
S
+
S
P
Enzyme
+
Substrate

ES complex
Enzyme
+
Products
Enzymes
can be
used to
break
down
molecules
Enzymes can also be used to
bond two substrates into one product
Reaction Rates
• Enzymes speed up reactions, so adding
more enzyme increases reaction rate…
Enzymes have “preferences”
• Enzymes function best in certain
conditions…we call these “OPTIMAL
CONDITIONS”
Factors affecting enzyme action
1. Temperature affects
molecular motion
a. An enzyme’s optimal
temperature produces the
highest rate
b. Most human enzymes work
best at 35-40 ºC.
WATCH OUT!!!
If the temperature gets too
high, the enzyme may be
denatured!
Temperature (cont.)
Optimum temperature
Reaction
Rate
Low
High
Temperature
Why does the reaction rate
decrease when temp gets too
high?
I’m not “Lion”
What does it
inject into your
body?
A PROTEIN
This protein is at the __________________
level?
What can we do to stop the
pain?
“BOIL” IT!
What did boiling “do” to the
protein?
BEFORE
AFTER
What does it mean when a protein has
been denatured?
Other than heat, what else can
denature a protein?
What happens if we denature
our enzymes?
Let’s See!!!
http://www.kscience.co.uk/animations/anim_2.htm
Denaturation of proteins
If an enzyme’s shape is changed so that it is
no longer able to catalyze reactions, we call
it…
DENATURED
• What kinds of things do you think could denature a
protein?
• High heat, strong pH, Extreme agitation, Heavy
metal ions.
2. Ions: Salt concentration & pH influence
enzyme activity.
a. SALT: The salt ions interfere with some
of the chemical bonds that maintain
protein structure
b. pH: The same is true of the extra
hydrogen ions at very low pH
1. Optimal pH for most enzymes near
neutral
3. Substrate Concentration
a. Increasing substrate concentration
increases the rate of reaction initially
(enzyme concentration is constant) Why?
b. Maximum enzyme activity will be reached
when all of enzyme combines with
substrate.
c. What would a graph of the above look like?
Substrate Concentration (cont.)
Maximum activity
Reaction
Rate
substrate concentration
Enzyme Inhibition
1. Inhibitors: cause a loss of catalytic activity
a. May change the protein structure of an
enzyme
b. May be competitive or noncompetitive
c. Some effects are irreversible
2. Competitive Inhibition
a. A competitive inhibitor
1. Has a structure similar to substrate
2. Occupies active site
a. “Competes” with substrate for active
site
3. Effects can be reversed by increasing
substrate concentration
Competitive Inhibition Image
3. Noncompetitive Inhibition
a. A noncompetitive inhibitor
1. Does not have a structure like substrate
2. Binds to the enzyme (not at active site) &
changes the shape of enzyme & active
site
a. Substrate cannot fit altered active site
3. No reaction occurs
4. Effect is not reversed by adding substrate
Noncompetitive Inhibition Image
Bellringer
PREDICT THE CHARACTERISTICS OF A
SUBSTRATE THAT WOULD BIND TO THE
FOLLOWING ACTIVE SITES.
• A large, polar active site
• A small, hydrophilic active site with an
acidic R group off to the left
• A small, hydrophobic active site
• A negatively charged active site with a
square shape.
Applications of Denaturation
a.
b.
c.
d.
Hard boiling an egg
Wiping skin with alcohol swab for injection
Cooking food to destroy E. coli
Autoclave sterilizes instruments
PEROXIDASE LAB
• Read prelab for homework!!!
In this lab- there are three reagents:
Turnip peroxidase
Hydrogen peroxide
Guiacol
Which is the enzyme?
Which is the substrate?
What is the other reagent then?!?
What kind of reaction is being
started in this reaction (breaking
down or building up?)
What are the products of this
reaction?
H2O2  H20 + O
How will we know if the reaction
occurred?
H2O2  H20 + O
Guiacol turns brown when oxidized.
(and it gets more and more brown as
more of the guiacol is oxidized).
How do we quantify “how brown” it is?
With a spectrophotometer!
So how did enzyme
concentration affect reaction
rate?
Results of the lab (graph)