“Prion” is a term coined by Stanley Prusiner, a scientist who won the Nobel Prize in 1997 for his work identifying and classifying the prion and linking it with various neurological diseases. It stands for proteinaceous infectious particle. The regular prion protein (PrP) is found in the cells of all mammals and does not cause disease, but the abnormal prion protein (PrPSc) is not and if it does enter a mammal it can cause disease. PrP and PrPSc have the identical amino acid sequences. PrP causes disease when it transforms, or folds differently, and becomes PrPSc. PrP sections that are shaped like a helix become pleated sheets in PrPSc (see Fig. 3).

     When a regular PrP enters a cell infected with PrPSc, contact with the PrPSc causes the normal PrP to fold into the abnormal PrPSc shape. Rather than reproducing itself, the abnormal PrPSc is responsible for transforming normal PrP. Because of its abnormal shape, PrPSc is not broken down by the enzyme protease, causing a buildup of the abnormal protein. Either the host cell bursts, releasing all of the PrPSc or the abnormal proteins collect on the surface of cells, forming plaques and killing the cells.