Catalysts
Reduces the amount of activation
energy needed for a reaction to take
place.

A type of catalyst.

A protein that speeds up a metabolic reaction by
lowering the activation energy needed.

Name usually ends in “-ase” and also indicates the
substrate it acts on. (ex: Lipase (breaks down…?)

Very small amounts needed


Reusable (are not changed or destroyed)
Highly specific

(ex: catalase only works on Hydrogen peroxide)
Examples: Digestive Enzymes
Digestive enzymes are
secreted along the digestive
tract.
Allow the nutrients in food
to be broken down and
absorbed into the blood stream.
Most produced by the
pancreas.
Human digestive enzymes
include ptyalin, pepsin, trypsin,
lipase, protease, and amylase.
Lactose intolerance
The inability to metabolize lactose,
a sugar found in milk and other dairy
products.
The required enzyme lactase is absent in the
intestinal system.
Symptoms of lactose intolerance include loose
stools, abdominal bloating and pain, flatulence,
and nausea.
Enzymes are affected by temperature, pH, concentration
*Can be denatured (change shape & lose function)
saturation point.
Activation energy energy required to start a reaction.
(with and without an enzyme)
Substrate & Active site

The substrate is the substance that the
enzyme is working on.

Active site – Where the
enzyme attaches to the
substrate.
Lock & Key Model
Competitive Inhibitor

Molecule competes for
the “active site”
Noncompetitive inhibitor

If the enzyme is an allosteric enzyme, the
presence of a noncompetitive inhibitor
changes the shape of the enzyme and
prevents the reaction from occurring.
Practice
1.
What is the area of an enzyme called where
the chemical reactions occur?
a. The Cytoplasm
b. The Active Site
c. The Catalyst
d. The Nucleus
Practice
2. What is the name of the enzyme that helps
to break down pectin in fruit to release more
of their juice?
a. Protease
b. Amylase
c. Glucose
d. Pectinase
Practice
3. Enzymes accelerate reactions by ___ the
activation energy needed for the reaction.
a. stopping
b. raising
c. lowering
d. binding
Practice
4. What happens to an enzyme when it denatures?
a. The activation energy of the reaction is doubled.
b. The activation energy of the reaction is lowered.
c. It's optimal conditions for temperature of the
enzyme are doubled.
d. The shape of the enzyme molecule is changed.
Practice
5. Which statement best describes the enzyme
represented in the graphs above?
a. This enzyme works best at a temperature of 35 C and
a pH of 8.
b. This enzyme works best at a temperature of 50 C and
a pH of 12.
c. Temperature and pH have no influence on the activity
of this enzyme.
d. This enzyme works best at a temperature above 50 C
and a pH above 12
Practice
6. A competitive inhibitor of an enzyme is
usually:
a. a highly reactive compound.
b. binds at a site other than the active site.
c. structurally similar to the substrate.
d. water insoluble.