Enzyme

Key Stage 3

Meaning

An enzyme is a biological molecule which can speed up a reaction or break down large molecules into smaller ones.

About Enzymes

Organisms have a number of different enzymes that control the chemical reactions that take place inside the cytoplasm.

Digestive enzymes are used to break down large insoluble food molecules into small soluble molecules.

The chemicals that an enzyme affects are called substrates.

Enzymes have an area called an active site which is where the enzyme interacts with the substrate.

The active site is shaped to fit with only one substrate so enzymes all have specific roles in an organism.

This diagram shows an enzyme, substrate and the active site of the enzyme.

Key Stage 4

Meaning

Enzymes are large proteins that can act as a catalyst for chemical reactions or be used to break down large molecules into smaller ones.

About Enzymes

Organisms have a number of different enzymes that control the chemical reactions that take place inside the cytoplasm.

Digestive enzymes are used to break down large insoluble food molecules into small soluble molecules.

The chemicals that an enzyme affects are called substrates.

Enzymes have an area called an active site which is where the enzyme interacts with the substrate.

The active site is shaped to fit with only one substrate so enzymes all have specific roles in an organism.

The fact that certain enzymes only work on certain substrates is explained by the Lock and Key Model.

This diagram shows an enzyme, substrate and the active site of the enzyme.

Denaturation

Enzymes can be denatured if the temperatures are too high or the pH is too extreme. Different enzymes have a different optimum temperature and optimum pH.

When an enzyme is denatured it changes shape so that the substrate will no longer fit the active site.

This diagram shows an enzyme before and after denaturation.

pH and Enzymes

Enzymes have an optimum pH at which they work best. If the pH is far from this optimum value the enzyme will denature.

This graph shows the optimum pH for amylase.

If the pH goes above 11 or below 2.5 all of the amylase enzymes will be denatured.

Temperature and Enzymes

Enzymes have an optimum temperature at which they work best. If the temperature is far above this optimum value the enzyme will denature. If the temperature is far lower the rate of reaction slows down due to the number of particle collisions being lower at lower temperatures.

This graph shows the optimum temperature for many enzymes in the human body.

If the temperature goes above 45 all of the enzymes will be denatured.

References

AQA

Enzyme, pages 207, 243, 253, GCSE Chemistry; Student Book, Collins, AQA

Enzyme, pages 64, 86-7, 96-103, 109, 170, 190, 246, 346-9, GCSE Biology; Student Book, Collins, AQA

Enzymes, page 154, GCSE Chemistry, Hodder, AQA

Enzymes, pages 109-111, 114-116, GCSE Combined Science Trilogy; Biology, CGP, AQA

Enzymes, pages 115- 117, 120-122, GCSE Biology, CGP, AQA

Enzymes, pages 125, GCSE Combined Science Trilogy 2, Hodder, AQA

Enzymes, pages 25-27, GCSE Combined Science; The Revision Guide, CGP, AQA

Enzymes, pages 28-31, GCSE Biology; The Revision Guide, CGP, AQA

Enzymes, pages 38-39, 42-49, GCSE Biology; Third Edition, Oxford University Press, AQA

Enzymes, pages 43, 45-50, 65, 125-6, GCSE Biology, Hodder, AQA