To discover the structure of a protein, we need about one tenth of a gramme of it in a pure state. This does not seem much, but each cell of an animal may contain only a few thousand molecules of the protein: as little as one millionth of a millionth of a millionth of a gramme !

In order to save bunny rabbits, we usually cause bacteria to make the proteins in which we are interested. The first stage in this process is to isolate and study the DNA which carries the blueprint for the protein. The aim here is to find out the order in which the four building blocks of DNA are assembled to form the famous double helix.

To read the message carried within the DNA, we use chemical reactions which produce different length fragments of DNA, depending on the order in which the four building blocks occur. These fragments are separated by loading them on top of a jelly-like material, down which we run an electric current.

Bigger pieces move slower in the gel, so that we get a ladder of fragments, from which we can read the sequence.

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