Biological Catalysts - Enzymes

introduction to enzymes and factors affecting rate of reaction.

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Chemical reactions keep you alive. Enzymes make chemical reactions work and speed them up as well.


A catalyst is a substance which increases the speed of a reaction, without being changed or used up itself.

Enzymes are all proteins.

All proteins are made up of chains of amino acids. These chains are folded up into unique shapes, which different enzymes need to do their jobs.

Chemical reactions usually involve things being either split up or joined together.

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Lock and key...

Chemical reactions usually involve things being either split up or joined together.

Every enzyme has a unique shape that fite onto the substance involved in a reaction.

Enzymes can usually only catalyse one reaction.

This is because for the enzyme to work the substance has to fit its special shape. If the substance does not match the enzymes shape then the reaction will not work.

Lock and Key Diagram (card 4)

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Factors affecting enzyme action

Changing the temperature changes the rate of the reaction

Like with any reaction, a higher temperature increases the rate at first, but if it gets too hot, the protein bonds holding the enzyme together break. This destroys the enzymes special shape, so it wont work anymore. It is said to be denatured.

Enzymes in the human body normally work best at around 37°C (Body Temperature)

The pH also effects enzymes. If its too high or too low, it interferes with the bonds holding the enzyme together. This changes the shape and denatures the enzyme.

All enzymes have an optimum pH that they work best at (beyond this point the enzyme denatures). It is often neutral, at pH 7. But not always. e.g. pepsin, the enzyme used to break down protein in the stomach works best at a very acidic pH 2.

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Lock and Key Model


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