MAKING SENSE OFENZYMES
IGCSE Biology1.1 Life Processes – Enzymes
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Learning Objectives• 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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Enzymes• 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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Why do we have enzymes?• 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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How do enzymes work?• 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.
Enzyme
SubstrateActive site
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How do enzymes work?
Enzyme
Substrate enters active site1
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How do enzymes work?
Enzyme Enzyme
Substrate enters active site An enzyme-substrate complex forms1 2
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How do enzymes work?
Enzyme Enzyme
Enzyme
Reaction occurs
Substrate enters active site An enzyme-substrate complex forms1 2
3
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How do enzymes work?
Enzyme Enzyme
EnzymeEnzyme
Products form and leave active site
Reaction occurs
Substrate enters active site An enzyme-substrate complex forms1 2
34
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Factors affecting enzymesTemperature• 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 10
20
30
40
50
60
70
Temperature (oC)
Rat
e of
rea
ctio
n
Optimum temperature
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Factors affecting enzymes
pH• 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
pH5 6 7 8 9
Rat
e of
rea
ctio
n
Optimum pH
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Can you describe a simple controlled experiment to show how enzyme
activity is affected by temperature?
• 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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The affect of temperature on the activity of amylase
WaterAmylase
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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The affect of temperature on the activity of amylase
WaterStarch 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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The affect of temperature on the activity of amylase
• 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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