Chapter 5 Section 5
Enzymes
Mrs. Kerstetter
Biology
Objectives
1.
2.
3.
Explain how enzymes affect activation energy.
Describe how an enzyme’s shape is important
to its function.
Describe how a substrate interacts with an
enzyme.
Enzymes
=specialized proteins that coordinate a cell’s activities
In order for a chemical reaction to begin, bonds need to be
weakened in the REACTANTS.
-reactants are the starting substances in a reaction
-PRODUCTS are the ending substances in a reaction
This activation process requires that the molecules ABSORB
energy
Activation Energy
=the start-up energy that activates the reactants
and triggers a chemical reaction
Some ways to activate reactants:
1. Heat-destroy a cell
2. Mix-not easy to do in a cell
3. Enzymes-”cell-friendly”
Enzymes
Cells rely on CATALYSTS to speed up a reaction
(rxn)
Main catalyst of chemical reactions in organisms
are specialized proteins called enzymes
Enzymes
-enzymes provide a way for rxns to occur at the
cell’s normal temperature
*Doesn’t supply activation energy to the reacting
molecules, but instead LOWERS the energy
requirements
Each enzyme catalyzes a specific kind of reaction
How Enzymes Work
Why do enzymes catalyze only one type of
reaction?
the shape of each enzyme only fits the shape
of its reactant molecules
*the specific reactant acted upon by an enzyme is
called its SUBSTRATE
*the region on the enzyme into which the
substrate fits is called its ACTIVE SITE
How Enzymes Work
-the fit between substrate and active site is not
rigid like a lock and a key
-more like a hand in a glove
-this positions the FUNCTIONAL GROUPS of
the active site in an area where it can catalyze a
rxn
How Enzymes Work
-most enzymes end in –ase
What type of reaction occurs as the water
molecule comes in and the substrate is
converted to products?
HYDROLYSIS
Product  glucose and fructose
-the products are released, and the enzyme can
now catalyze another sucrose molecule
How Enzymes Work
Another way that enzymes can lower activation
energy is by accepting TWO reactant molecules
into adjacent sites
Enzyme's structure and shape are essential to its
functions
*pH and temperature affects how well or if an
enzyme works at all
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Chapter 5 Section 5 Enzymes