http://www.ck12.org Chapter 3. Chemical Interactions
3.44 Enzymes as Catalysts
- Define enzyme.
- Explain why chemical reactions in living cells require enzymes.
- Describe how enzymes work.
- Identify two human digestive enzymes.
An enzyme cleaner like the one pictured here contains proteins called enzymes. The enzymes attach themselves to
particular stains and help break them down. Different enzymes work on different types of stains, such as grease
stains or bloodstains. Removing stains isn’t the only use of enzymes. Enzymes are also essential to life.
Why Living Things Need Enzymes
Chemical reactions constantly occur inside the cells of living things. However, under the conditions inside cells,
most biochemical reactions would occur too slowly to maintain life. That’s where enzymes come in.Enzymesare
catalysts in living things. Like other catalysts, they speed up chemical reactions. Enzymes are proteins that are
synthesized in the cells that need them, based on instructions encoded in the cells’ DNA.
How Enzymes Work
Enzymes increase the rate of chemical reactions by reducing the amount of activation energy needed for reactants
to start reacting. One way this can happen is modeled in theFigure3.84. Enzymes aren’t changed or used up in
the reactions they catalyze, so they can be used to speed up the same reaction over and over again. Each enzyme
is highly specific for the particular reaction is catalyzes, so enzymes are very effective. A reaction that would take
many years to occur without its enzyme might occur in a split second with the enzyme. Enzymes are also very
efficient, so waste products rarely form.