Grade 10 - Enzymes
Enzyme Action
Changing Reaction Rates
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Certain factors help speed up reactions which
normally would take a long time to proceed.
An example of this is when Hydrogen Peroxide
breaks down to form water and oxygen:
o

2H2O2
2H2O
(Hydrogen Peroxide)
(Water)
+
O2
(Oxygen)
When this reaction is heated, the reaction rate
(amount of chemical change per unit time)
increases!
o The energy (e.g. Heat) required to make any chemical
reaction proceed is called the ACTIVATION ENERGY
Catalysts
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Not only does heat (temperature) effect the
reaction rate, but other chemicals also help speed
the reactions up.
Manganese Dioxide is a chemical which helps the
Hydrogen Peroxide reaction proceed faster.
o A substance which increases the rate of reaction is
called a CATALYST.
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There are also biological (protein) catalysts and
these are called ENZYMES!
Enzymes are protein molecules which occur
naturally in all living cells.
Catalase is an enzyme found in liver cells which
helps speed up the Hydrogen Peroxide reaction.
Properties of an Enzyme:

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Biological Catalyst
Lowers the energy input/activation energy required for a
chemical reaction to proceed.
Speeds up rate of reaction
Enzymes are proteins
Enzymes remain unchanged after a reaction and therefore
can work again.
Enzymes are specific to a substrate of a reaction (Lock and
Key).
Enzymes are reversible and can catalyse a reaction going
both ways (Synthesis/Lysis)
Enzymes are denatured by:
o Change in Temperature
o Change in pH
Therefore have an optimum
Temperature and pH, where it works
most effectively. In Humans that is
usually around 37˚C and a pH of 7.
Catalase experiments
Activation energy with/without Enzymes
(Substrates)
(Products)
Specificty of Enzymes

Lock and Key Mechanism:
o On Enzyme surface there is the active site which fits specifically
with the substrate molecule it is suited to work on.
Active
Site
SUBSTRATE
Active Site unchanged, can now
work on a new substrate.
ENZYME-SUBSTRATE
COMPLEX
PRODUCTS
Degradation of Complex Substrate

Degradation/lysis (breaking down) of complex substrate
Synthesis of Complex Product

Synthesis (building up) of complex product
Effect of Amylase Enzyme on starch (Degradation)
STARCH
glucose
glucose
glucose
glucose
glucose
glucose
Amylase Enzyme
glucose
glucose
glucose
glucose
Amylase Enzyme
glucose
glucose
glucose
glucose
Amylase Enzyme
glucose
glucose
Effect of phosphoraylase on Glucose-1phosphorylase (Synthesis)
Glucose-1-Phosphate
How do you test for starch?
(Iodine)… so wouldn’t this be
a good test to see the effect of
Phosphorylase
Phosphorylase Enzyme
Bond forming between two
Glc molecules
Glucose-1-Phosphate
Phosphorylase Enzyme
Ect………….
STARCH molecule formed
Phosphorylase Enzyme
The equations for the previous reactions:

Effect of amylase (degradation)
o Starch
Maltose (simple sugar)
(Substrate)
(Products)
Amylase

Effect of potato phosphorylase (synthesis)
o Glucose-1-phosphate
(Substrate)
Starch
(Products)
Potato Phosphorylase
Effect of Temp/pH on Enzyme Activity
Rate of Reaction/Enzyme Activity
Optimum
Temp/pH for
enzyme
activity!
Enzyme is becoming
denatured (the active site is
being physically altered
(permanent damage)
Temp/pH (Arbitary units)
Digestion of starch by amylase
pH and Enzyme activity