Name _______________________________
Class __________________
The chemical reactions that occur in the cells of living things take place in part
because of the actions of biological catalysts called enzymes. Each type of enzyme
catalyzes only one type of reaction, and since thousands of different kinds of
reactions occur in cells, thousands of different enzymes exist. All enzymes are
proteins, so they are created though the mechanism of protein synthesis.
Energy must be supplied in order for most cellular chemical reactions to proceed. The
initial input of energy required to start a reaction is called activation energy. As is
shown in the diagram called Enzyme Function, chemical reactants (A – RED) can be
converted into products (B – GREEN) only after a substantial input of energy.
Enzymes act to lower the activation energy of chemical reactions; therefore reactants
(C – RED) react more quickly to form products (D –GREEN ) because the activation
energy of the reaction is far less.
An enzyme (E – PURPLE) is a biological catalyst that speeds up a chemical reaction
without itself being changed. Enzymes’ names can be easily recognized because they
usually end in –ase. For example, the enzyme protease acts on protein, and lactase acts
on lactose. Some enzymes are named specifically according to the type of reaction
they catalyze. One example of this is synthetase, which catalyzes synthetic reactions.
A key portion of the enzyme is the active site (E1 – RED). The active site is the region
in which reactants bind and, essentially, the region in which the chemical reaction
takes place. To operate enzymes first need to have a reactant, called a substrate that
binds loosely to the active site. In reaction 1 (arrow 1 –GREEN) we see the enzyme and
substrate combine at the active site. This reaction forms what is known as an enzymesubstrate complex. In reaction 2 (arrow 2 – YELLOW), a chemical change takes place
at the active site and the result is the formation of two products (G – BLUE). In
reaction 3 (arrow 3 – ORANGE), the products are released from the active site and
the enzyme is recycled for use in another reaction.
There are numerous ways in which enzymes can be inhibited, or changed. For example,
heat can denature, or change its structure, making it unable to bind to a substrate.
Enzymes can also be denatured by acidic or basic environments.
Many chemical substances interfere with the activity of enzymes by binding to them,
and these are referred to as inhibitors. Inhibitors are classified by the way in which
they bind to an enzyme. Notice that the enzyme (E) can react with the substrate (F) as
well as with an inhibitor (H – BROWN). In these cases, there is competition for the
enzymes’ active site. When large mounds of the inhibitor are present, it is more likely
that the inhibitor, and not the substrate, will bind at the active site, as shown in
chemical reaction 2. Once the inhibitor is locking the active site, the substrate
molecule cannot bind, as you can see in reaction 3, and no chemical reaction will
occur.
Name _______________________________
Class __________________
Enzyme Questions and Coloring
Questions
1. What is an enzyme? _______________________________________________________
2. All enzymes are _______________, that are created through protein synthesis.
3. The initial input of energy required to start a reaction is called ___________ _________.
4. Enzymes act to ____________ the activation energy of chemical reactions.
5. Enzymes end in ____________.
6. The region in which reactants bind and the chemical reaction takes place is called the
____________ ___________.
7. What are ways enzymes can be inhibited or changed? __________________________
______________________________________________________________________
8. What is an inhibitor? _____________________________________________________
Color and Label