In order to develop, grow, and reproduce, biological organisms
depend upon thousands
of chemical reactions. These reactions are called biochemical
reactions and they occur
because of specialized catalysts called enzymes. Although these
enzymes do not force
a reaction to occur that would not occur otherwise, they greatly
increase the rates of
body reactions that allow us to produce the energy we need to
survive. If it were not
for these biochemical catalysts, our body reactions would be so
slow that life would
be impossible.
Over 2,000 different enzymes in the body are known. This large
number is necessary
because enzymes are very particular about the reactions they
catalyze; in fact, an
enzyme may catalyze only one specific reaction. Enzymes are
present in every body cell.
One enzyme, which we will study in this module, is the enzyme catalase.
It is produced
in small organelles called peroxisomes, or microbodies.
The enzyme catalase breaks
down harmful hydrogen peroxide when it is produced excessively by
body cells.
All enzymes are protein molecules. Although very large protein
molecules, there is
one primary area of the enzyme molecule where it chemically
reacts with a substance
called a substrate. This part of the molecule is called
the active site. We can understand
how an enzyme works by comparing its action on a substrate
molecule to that of a
key in a lock. The ridges and grooves of the key represent the active
site of the
enzyme, and, just as each key fits only a particular lock, each
enzyme fits only a
particular substrate. Also, just as the key opens the lock and is
not destroyed in the
process, enzymes—like other catalysts—emerge intact
from a biochemical reaction.
Sometimes other molecules block enzymes or otherwise interfere
with their reaction
at the active site. These species include certain metal ions,
insecticides, poisons, and
bacterial toxins (like botulin that produces botulism). This
process is called enzyme
inhibition.
Enzymes act on substrates at a very rapid rate. One catalase
enzyme molecule, for
example, will completely break down 5.6 million hydrogen
peroxide molecules per
minute. Catalase is considered a relatively slow enzyme! One
of the fastest enzymes,
carbonic anhydrase, will break down 36 million carbonic acid
molecules per minute.
Now that’s fast!
Since enzymes are protein molecules, they have the properties of
proteins. They are
denatured (rendered inactive) by high temperatures and many by
extremes in pH.
As the temperature of an enzyme-catalyzed reaction increases, the
rate increases
until the temperature is high enough to denature the protein.
This is an enrichment topic. It is most appropriate for the
student who has had a
general chemistry course.
1. Enzymes are special molecules that catalyze
biochemical reactions.
2. All enzymes are protein molecules, and have
general properties of proteins,
i.e., they are altered by pH and temperature changes.
