Transcript 3 Enzyme Notes

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
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!
Structure
1. 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?
Denaturation
a. Disruption of protein structure by
1. Heat: Break apart H bonds and disrupt
hydrophobic attractions
2. Acids/ bases: Break H bonds between polar
R groups and ionic bonds
3. Heavy metal ions: React with S-S bonds to
form solids
4. Agitation: Stretches chains until bonds
break
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
Think about it
Tannic acid is used to form a scab on a burn.
An egg becomes hard boiled when placed in
hot water. What is similar about these two
events?
Solution
Acid and heat cause a denaturation of
protein. They both break bonds in the
structure of protein.
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
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