Describe what is meant by the 'lock and key' theory.

When binding two things together in biology, such as an enzyme and a substrate, in order to fit together they musth ave a specific shape. The shape of the enzyme active site must be the reciprocal to the shape of the substrates binding site, they are the opposite to each other so they can fit together. Each enzyme and substrate have a different active site and therefore only a few will be able to interact with each other, ie. there are several 'locks' (the enzyme) and several easy (the substrate) but the key may not necessarily open the lock, (the enzyme may not be activated).