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INTRODUCTION TO ENZYMES
FACT SHEET FOR CATALASE MAJOR LAB
Most chemical reactions in the body, if carried out in a test tube with only reactants and products present, would
proceed at very low rates because they have high activation energies (energy required for chemical bonds to
be broken or formed). What provides chemical reactions (e.g. the synthesis of macromolecules like
polysaccharides) the activation energy to initiate? Biological catalysts are required to lower activation energies.
Enzymes are protein catalysts.
An enzyme works by coming into contact with a reactant (which are called substrates). The substrate becomes
bound to the enzyme, forming an enzyme-substrate complex (see figure 1). This complex helps to break down
(or strengthen) the chemical bond to release products and the enzyme. The reaction can be thought of as this:
Substrate + Enzyme  Enzyme-Substrate Complex  Product + Enzyme
When the reaction is complete, the enzyme is free
to run the same reaction with additional substrate
molecules. So, in an enzyme-catalyzed reaction,
the enzyme itself should remain unchanged after
the reaction.
Enzymes and substrates have specific ways of
interacting to carry out these reactions. A special
site on the enzyme, known as the active site is
specific in shape and chemical affinity for its
substrate. The shape of the active site is
Figure 1: Enzyme-Substrate Complex
complimentary to the substrate’s shape. You can
think of an analogy of a key fitting into a lock to
visualize how an enzyme’s active site works with
the shape of its substrate. In a typical animal cell, there are around 4000 enzymes which are capable of
catalyzing a chemical reaction.
Most enzymes are named with the suffix –ase and the name of the enzyme generally matches with its function.
For example, the enzyme carbonic anhydrase is responsible for breaking down carbonic acid into carbon dioxide
and water.
There are a variety of factors which can influence enzyme activity, which you will investigate in this summative
lab. Some of these factors include (but are not limited to): presence of allosteric activators/inhibitors,
temperature, pH, concentration of enzyme, and concentration of substrate. Table 1 below serves as a summary
of important fundamental enzyme characteristics:
Table 1: Important characteristics of enzymes
1. An enzyme itself remains unchanged after the reaction it catalyzes
2. The binding of a substrate to an enzyme’s active site has the same characteristics
as a ligand binding to a protein
3. An enzyme increases the rate of a chemical reaction, but does not cause a reaction
to occur that would not occur in its absence
4. An enzyme lowers the activation energy of a reaction but does not change the net
amount of energy that is added to or released by the reactants in the course of a
reaction.
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Practice Questions for Understanding:
1. Complete the missing labels a, b, c, and d on the diagram below:
2. Decide if each of the statements below is true or false:
a. Enzymes interact with specific substrates _____
b. Enzymes change shape after a reaction has occurred _____
c. Enzymes speed up reactions _____
d. One enzyme can be used for many different types of chemical reactions _____
e. Enzyme reactions can be slowed down or stopped given extreme conditions _____
3. Without enzymes, reactions would not have enough ________________ to occur.
4. Define the following terms in your own words:
o
Active Site
o
Substrate
o
Activation Energy
5. Complete the blanks in the following passage:
Enzymes are biological ___________________. They ________________ the rate at which chemical reactions
occur in living cells. They are organic compounds composed of ___________ macromolecule. Enzymes are
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SBI4U
important facilitators of energy-transforming reactions, recycling processes, synthesis of some biomolecules and
breakdown of biomolecules,