Transcript ENZYME NOTES

Enzymes
Characteristics of Enzymes
1. Proteins
2. Catalysts
a. Speed up chemical
reactions without
being used up
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. The name usually relates to the reactants
they are associated with or the reaction
they help start
a. Examples: maltase, 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
E
+
S
ES complex
E
+
P
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.
e.
f.
Hard boiling an egg
Wiping skin with alcohol swab for injection
Cooking food to destroy E. coli
Heat used to cauterize blood vessels
Autoclave sterilizes instruments
Milk is heated to make yogurt
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?
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