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The need for speed

Thousands of different chemical reactions must happen inside every cell, every second in order for them to function. If these cellular reactions happen too slowly the cell may die. If the cell is part of a multicellular organism then this might also harm the whole individual.

For example, in liver cells the toxic chemical hydrogen peroxide must be broken down into harmless products, water and oxygen. If this reaction happens too slowly then hydrogen peroxide can build up and poison the cell.

The rate of a chemical reaction can be increased in the laboratory by increasing the temperature. This gives more molecules sufficient energy to react with each other. However, in the body high temperature cannot be used to speed up reactions as this would damage cell proteins and prevent them from functioning.

Living cells solve this problem by producing proteins called enzymes. Enzymes speed up cellular reactions at body temperature by providing a more favourable environment for the reacting molecules to meet in. They also remain unchanged by cellular reactions and therefore can be reused by the cell.

The chemicals that enzymes act upon are called substrates. The chemicals produced by the action of an enzyme are called products.

For example, liver cells produce the enzyme catalase to speed up the breakdown of hydrogen peroxide:

In this example the enzyme catalase acts on the substrate hydrogen peroxide and the products are water and oxygen.

The effect of catalase on hydrogen peroxide can be investigated in the lab. Watch the video below to see the correct procedure for carrying out this experiment.

Enzyme structure

Enzymes are proteins. Their amino acids fold into three-dimensional structures that can be represented by simple shapes.