proteins

Proteins are made up of chains of amino acids, and are often folded up into a ball shape. The picture to the right shows a typical protein folded up. There are 20 different sorts of amino acid, each with slightly different properties, and these are often grouped together which is why some of the 'balls' in this image, each of which represents a different amino acid in the chain, are coloured, so that you can quickly see the amino acids with similar properties.
Since we know that there are 20 different amino acids, you can work out roughly how many different sorts of protein there could be.