BIOLOGY

1. MAKING SENSE OF
ENZYMES
IGCSE Biology
1.1 Life Processes – Enzymes
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2. • 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? (Separate science only)
• Can you describe a simple controlled
experiment to show how enzyme activity is
affected by temperature?
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3. • 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.
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4. • 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.
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5. • 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.
Substrate
Active site
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6. Substrate enters active site
1
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7. Substrate enters active site An enzyme-substrate complex forms
1 2
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8. Reaction occurs
Substrate enters active site An enzyme-substrate complex forms
1 2
3
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9. Products form and leave active site
Reaction occurs
Substrate enters active site An enzyme-substrate complex forms
1 2
3
4
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10. • Each enzyme has an optimum
temperature at which it works
best.
• Above this temp the shape of
the enzyme’s active site is
changed by the heat.
• The enzyme becomes
DENATURED and stops
working.
0 1
0
2
0
3 4 5 6 7
0 0 0
o
0 0
Temperature ( C)
Rate
of
reaction
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11. • The optimum pH for most
enzymes is pH 7.
• Although enzymes in the
stomach can work at pH 2.
This slide is for separate
science only
5 6 7
pH
8 9
Rate
of
reaction
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12. • 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.
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13. Amylase
Water
Starch
• Get your water to the
required temperature using a
Bunsen burner.
• Allow 10 minutes for the
starch and amylase to reach
the same temperature.
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14. Water
Starch and
amylase mixture
• 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.
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15. • 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.
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16. Terms and Conditions
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