Scrapie proteins. Coloured transmission electron micrograph (TEM) of scrapie-associated protein strands taken from the brain of an infected hamster. Scrapie is a transmissible spongiform encephalopathy (TSE), which causes brain degeneration in some animals. The causative agent is thought to be a prion, an abnormal version of a protein naturally present in brain cells. The prion protein is not as easily degraded by cellular enzymes as the natural version and accumulates within nerve cells, destroying them. Prion proteins are also thought to cause the human TSE Creutzfeldt-Jakob disease (CJD). Magnification: x49,720 at 6x7cm size.