This document provides information about enzymes and how they function as biological catalysts in metabolic reactions. It discusses that enzymes are proteins that speed up chemical reactions in cells and do not get used in the reactions. The document describes how enzymes have an active site that binds to substrate molecules in a lock-and-key mechanism. It explains that temperature and pH can affect the shape of the active site and enzyme function, with most enzymes working best around body temperature and pH 7. It proposes a simple experiment using the enzyme amylase to show how reaction time is affected by temperature.

1. IGCSE Biology – 4BI0
MAKING SENSE OF
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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?
• Can you describe a simple controlled
experiment to show how enzyme activity is
affected by temperature?
• How are enzymes affected by pH? (Separate science only)
1.1 Life Processes - Enzymes
Objectives
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• 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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1.1 Life Processes - Enzymes
What are enzymes?

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1.1 Life Processes - Enzymes
What are 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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1.1 Life Processes - Enzymes
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.
SubstrateActive site

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1.1 Life Processes - Enzymes
How do enzymes work?
Substrate enters active site1

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1.1 Life Processes - Enzymes
How do enzymes work?
Substrate enters active site An enzyme-substrate complex forms1 2

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1.1 Life Processes - Enzymes
How do enzymes work?
Substrate enters active site1 2
3

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1.1 Life Processes - Enzymes
How do enzymes work?
Products form and leave active site
Reaction occurs
Substrate enters active site An enzyme-substrate complex forms1 2
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1.1 Life Processes - Enzymes
Factors affecting enzymes
• 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.
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0
2
0
3
0
4
0
5
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6
0
7
0
Temperature (oC)
Rateofreaction

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1.1 Life Processes - Enzymes
Factors affecting enzymes
• The optimum pH for most
enzymes is pH 7.
• Although enzymes in the
stomach can work at pH 2.
pH
5 6 7 8 9
Rateofreaction
This slide is for separate
science only

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1.1 Life Processes - Enzymes
Factors affecting enzymes
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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1.1 Life Processes - Enzymes
Factors affecting enzymes

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1.1 Life Processes - Enzymes
Factors affecting enzymes

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1.1 Life Processes - Enzymes
Factors affecting enzymes
• 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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