THE ROLE OF ENZYMES
ENZYMES SPEED UP CHEMICAL REACTIONS.
Everything that happens in a cell
 Growth
 Reproduction
 Interaction with the environment
 Response to stimuli
Is the result of a chemical reaction.
A chemical reaction is a change in the arrangement
of atoms or molecules that yields different substances
CHARACTERISTICS OF CHEMICAL REACTIONS
All chemical reactions involve reactants and
Products.
Reactants are the atoms, molecules or compounds
that enter a into a chemical reaction.
Products are the atoms, molecules or compounds
that result from the reaction
Chemical reactions break chemical bonds in one or more
reactants and form new bonds in one or more products.
Photosynthesis
Reactants
Products
(light energy)
Carbon
Dioxide
CO2
+ water
H2 O
Glucose
C6H12O6
+
Oxygen
6O2
The biochemical reactions in living things must
occur at certain spped or rate to be useful.
Rate of a chemical reactions depends on:
 Temperature
 The concentration of reactants
 Surface area
 The presence of a catalyst
A catalyst is a substance that speeds up the rate of
a chemical reaction without being changed by the
reaction.
An enzyme is a protein that is a biochemical
catalyst.
Enzymes make chemical reactions within cell
possible or speed them up.
Enzymes give reactants a site where they can
come together.
The surface of an enzyme has a distinct shape
that allows it to interact only with certain
substrates.
Organisms have thousands of enzymes
Substrates bind to a part of the enzyme called the
active site. The shape of the enzyme and substrate are
Complementary.
Enzymes can form to the shape of its substrate.
They
I fit together much like a lock and key.
When the reaction finishes, the products are
released. The enzyme, which is unchanged ,
can then repeat the process. It is not used up
http://en.wikipedia.org/wiki/File:Induced_fit_diagram.svg
Life Sciences-HHMI Outreach. Copyright 2009 President and Fellows of Harvard College
ACTIVATION ENERGY
For a chemical reaction to occur, reactants must
come together with enough energy to break
existing bonds and form new ones.
Enzymes speed up chemical reactions by reducing
the amount of energy that the substrates need in
order to react.
The activation energy is the minimum amount
energy needed for colliding molecules to react.
ENZYME ACTIVITY CAN BE AFFECTED BY:
Temperature
 pH
 Concentration of enzyme-substrate
Temperature
Enzymes for different organisms tend to work
best at different temperatures.
In humans is about 37°C, in plants 25°C.
Enzymes are usually destroyed or denatured at
temperatures above 50°C. Denaturing changes the
shape. Without the correct shape enzymes won’t
function properly.

pH
The pH of a solution describes how acidic or basic
the solution is. Most enzymes function in narrow
pH ranges.
1. What best describes how enzymes
function in the body?
a. Enzymes are converted into products by
the reactions they catalyze.
b. Enzymes lower the activation energy of
reactions
c. One enzyme can catalyze many different
reactions.
d. An enzyme is used once and then
destroyed by the cell
2. The diagram below illustrates a
biochemical process that occurs in
organisms. The substance labeled catalyst
is also known as a(n)
a.
b.
c.
d.
antibody
enzyme
hormone.
inorganic compound
3. The enzyme catalase is involved in the
breakdown of hydrogen peroxide into water
and oxygen. During this reaction, the
catalase
a.
b.
c.
d.
is unchanged.
is used up.
is changed into a product.
is formed into a new enzyme
4. Catalysts may reduce the amount of activation
energy required for a chemical reaction to occur.
Platinum (Pt) is a catalyst that is used in catalytic
converters in automobiles.
In the graphs below, pathway x is a solid line
representing the uncatalyzed reaction.
The dotted line shows the catalyzed reaction.
Which graph best illustrates the changes in a reaction
when the catalyst reduces the amount of energy
required?
a.
b.
c.
d.
5. Even within a single cell, there are a great number of
different enzymes. Why are there so many different kinds
of enzymes?
a. Enzymes are made out of amino acids and fold up into
different shapes so they can do different jobs in the cell.
If one enzyme quits working, another one can take its
place. That way the cell can stay active and keep
functioning even if some of the enzymes cannot function.
b. Each enzyme is shaped to do one specific task. An
enzyme shaped so that it can break down one molecule
cannot be used to break down a different molecule.
There must be enough different types of enzymes within
a cell to do all the tasks the cell requires.
6. Enzymes are used throughout our bodies to
build up or break down molecules. Describe how
an enzyme breaks down a large molecule into
smaller ones.
a. Enzymes are made out of proteins. They have a spot
called an active site that can hold a molecule and force the
molecule to come apart at the right spot. A protein
molecule could fall into the active site of an enzyme and it
would break into amino acids. Then a carbohydrate
molecule could fall into the active site after the amino acids
float away and the enzyme would break it into simple
sugars.
b. Enzymes are long chains made of amino acids folded
into very specific shapes. The active site forms on one side
of the enzyme as it folds up. It is shaped like the molecule
that the specific enzyme will work on. When the right
molecule comes into contact with the active site, the
enzyme and molecule bind. This puts strain on the bonds in
the molecule, causing the molecule to break at the correct
spot.
7. As food travels through the digestive system, it is
exposed to a variety of pH levels. The stomach has a
pH of 2 due to the presence of hydrochloric acid
(HCl), and the small intestine has a pH ranging from
7 to 9. HCl converts pepsinogen into pepsin, an
enzyme that digests proteins in the stomach.
Which of the following most likely happens to pepsin
as it enters the small intestine?
A. It becomes inactive.
B. It begins to replicate.
C. Its shape changes to engulf large proteins.
D. Its activity increases to digest more proteins.