Enzymes, Biology O-Level IGCSE

1. ENZYMES
The workers in our body

2. WHAT ARE ENZYMES?
 They are biological catalysts.
 A catalyst is a chemical that can speed up chemical
reactions without being changed or used up.
 They are molecules made of protein that have a certain
shape “dent” to attach to a certain molecule.

3.  The molecule to which an enzyme attaches is
called a substrate.
 The site of attachment is called the active site
 The molecule(s) resulting from the catalytic reaction
is named the product(s).
 The theory developed to explain how enzymes
work is called the key and lock theory.
Enzyme-substrate
complex

4. ENZYME PROPERTIES
 Enzymes are made of proteins.
 They are “specific”= they can only work on one
type of molecule.
 Their activity is affected by changes in temperature.
 Their activity is a affected by changes in pH.
 Every enzyme has a temperature at which it works
best; it is called the optimum temperature.
 Every enzyme has a pH at which it works best; it is
called the optimum pH.
 The enzyme would not be active if its active site is
permanently changed, we say it is denatured.

5. EFFECT OF TEMPERATURE
 As the temperature
increases, molecules
gain more kinetic energy
and move faster.
Bumping into each other
more often, this speeds
up the reaction. But if the
temp rises above the
optimum the enzyme’s
shape changes and it no
longer works; it is now
denatured.

6. EFFECT OF PH
 If the solution where
enzymes work becomes
more acidic or more basic
this changes the lengths
of the bonds holding it in
that special shape. The
farther away from the
optimum pH the more the
change in the enzyme’s
shape. It is also
denatured by extreme
changes in pH.

7. EFFECT OF ENZYME CONCENTRATION
 As the concentration of
enzymes increase
more active sites are
available to speed up
the reaction.

8. EFFECT OF SUBSTRATE CONCENTRATION
 As the concentration of
substrate increases the
chance of a substrate
bumping into the
enzyme increases. This
speeds up the reaction.
 After a certain
concentration; adding
more substrate doesn’t
speed up the reaction.

9. EFFECT OF SURFACE AREA
 If both of these cells
had digestive enzymes
on their cell membrane
to digest food that has
reached the small
intestine. Which of
these cells will the
enzymes finish their job
faster?
A
B

10. As the
reaction
proceeds the
amount of
substrate
decreases
while the
amount of
product
increases.
This
continues till
the reaction
stops.