Enzymes are proteins which act as catalysts for bio-chemical reactions within the cells of the body. They speed up a chemical reaction, but are not affected or changed by it, so they can be used over and over again. Enzymes will only catalyse with one specific reaction (substrate), because they are very selective.

The reaction that takes place is when a molecule entering what is know as the substrate bonds to a specific site on the enzyme. This is called the active site. Whilst the substrates are bound to the enzymes the reaction proceeds, and it is only when it is complete that the reaction breaks away from the enzyme, ready to be used again.

There are two enzyme theories as to how the activation takes place

·        Lock & key

·        Induced fit

Lock & key reaction

The lock and key reaction is where the substrate can fit precisely on to the active site of the enzyme molecule. The active site contains chemical groups which attract the substrate to it resulting in the catalyse reaction. This is the hypothesis where only certain substrates will fit, due to the fact of the enzyme-controlled reaction.