Mr Exham IGCSE Biology - Enzymes

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?


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.


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.


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


How do enzymes work?

Enzyme

Substrate enters active site1



Enzyme Enzyme

Substrate enters active site An enzyme-substrate complex forms1 2



Enzyme Enzyme

Enzyme

Reaction occurs


3



Enzyme Enzyme

EnzymeEnzyme

Products form and leave active site

Reaction occurs


34


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


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


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.


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.



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.



• 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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