Prion protein. Computer model of the prion protein responsible for causing CJD (Creutzfeldt-Jakob disease) in humans, superimposed on a CT (computed tomography) scan of a brain. The prion is a mutated form of a normal cell protein (PrP). This prion comprises spiralling alpha helices (orange) and straight beta sheets (green). The C and N represent the carbon and nitrogen ends of the amino acid structure respectively. Both BSE and CJD are brain-wasting disorders characterised by progressive dementia and a rapid deterioration in co-ordination, leading inevitably to death.