MAKING SENSE OF
ENZYMES
IGCSE Biology
1.1 Life Processes – Enzymes
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• Can you explain the role of enzymes as biological
catalysts and how they are used in metabolic
reactions?
• How can enzyme function be affected by
temperature?
• How are enzymes affected by pH?
• Can you describe a simple controlled experiment to
show how enzyme activity is affected by
temperature?
• All chemical reactions that happen in a cell are
controlled by enzymes.
• Enzymes are biological catalysts.
• This means they speed up the reaction and do not
get used up in the reaction.
• They are all proteins which are coded for by genes.
• The function of enzymes is to catalyse metabolic
reactions.
• Our body temperature is 37oC
• This is quite a low temperature for reactions to take
place.
• Without enzymes the reactions in our bodies would
occur too slowly to support our body’s needs.
• Each enzyme has an active site.
• The molecule that it wants to help change is called
the substrate.
• The active site fits the substrate like a lock and a key.
Active site
Substrate
1 Substrate enters active site
1 Substrate enters active site
2
An enzyme-substrate complex forms
1 Substrate enters active site
2
An enzyme-substrate complex forms
3
Reaction occurs
1 Substrate enters active site
2
4
3
An enzyme-substrate complex forms
Reaction occurs
Products form and leave active site
• Above this temp the shape of
the enzyme’s active site is
changed by the heat.
• The enzyme becomes
DENATURED.
Rate of reaction
• Each enzyme has an optimum
temperature at which it works
best.
0
1
0
2
0
3
0
4
0
5
0
6
0
Temperature (oC)
7
0
• Although enzymes in the
stomach can work at pH 2.
Rate of reaction
• The optimum pH for most
enzymes is pH 7.
5
6
7
pH
This slide is for separate
science only
8
9
• Amylase is a good enzyme to investigate.
• It is used in digestion to breakdown the starch
you eat into sugar.
• You can test for starch using iodine.
• If there is starch present the solution will
change colour from the initial brown/yellow
colour to blue/black.
• Get your water to the required
temperature using a Bunsen
burner.
• Allow 10 minutes for the starch
and amylase to reach the same
temperature.
Starch
Amylase
Water
• Mix the starch and amylase together.
• Remove a sample from the test tube
every 30 seconds using a pipette.
• Place it into a spotting tile and test
with iodine to see how much starch is
left.
• See what the total time in seconds is
for the starch to be broken down.
Water
Starch and
amylase mixture
• Choose five temperatures to investigate in the range of 10oC to
80oC.
• Repeat the same procedure for each temperature making sure
that all other variables are kept constant between each
experiment.
• For a control experiment you could use boiled amylase instead
of normal amylase.
• To make the experiment more reliable repeat each temperature
3 - 5 times and take the average time.
• Plot the results as a graph of temperature on the x-axis against
time on the y-axis.