The relationship between the structure and function of proteins is an important area in biochemistry. Pupils studying A-level Biology are introduced to the four levels of protein structure (primary, secondary, tertiary and quaternary) and how these can be used to describe the progressive folding of a chain of amino acid residues to a final, functional, three-dimensional shape. The activity described in this "Science Note" makes use of the computer models of protein structures that are used by professional scientists to allow pupils to visualise and "manipulate" individual proteins. This practical activity has been developed with AS-level candidates (age 17-18 years) over two successive years at an 11-19 non-selective, co-educational school in England. The predicted grades of the class ranged from E to A. This activity was found to be beneficial for pupils across the full ability range. Examples of the pupils' opinions are included in this report. (Contains 2 boxes, 2 figures, 1 table, and 3 online resources.)