Pions is discovered by a man named Stanley Prusiner. Before his discovery it is known as 'slow virus' cause of it long dely between infection and th onset of signs and symptoms. Prions is a proteinaceous infectious agent that was different from any other known infectious agent in that it lacked nucleic acid. Scientists resisted the concept of prions because particles lack any nucleic acids violate the 'universal' rule of protein sythesis. Proteins are translated from a molecule of mRNA, and the information is a copy of a DNA molecules. So how can prions carry the information required to replicate themselves?

Prions are single proteins, called PrP, and all mammals contains a gene that codes for the primary sequence of amino acids in PrP. Normal, functional structure that folds with several apha-helices, called cellular PrP and the disease causing form having beta-pleated sheets, called prion PrP. Prion PrP is able to convert normal cellular PrP into prion PrP by inducing the conformational change in the shape of cellular PrP. The prion PrP will cause the cellular PrP to refolds to form prion PrP, forming more prions. Thus, the rule of proteins synthesize is maintained as prions do code for new prions but instead convert extant cellular PrP into prions. Prion diseases involve fatal neurological degeneration, the deposition of fibrils in the brain, and the loss of brain matter such that eventually large vacuoles form.

Scrapie is a fatal, degenerative disease affecting the central nervous system of sheep and goats.This disease is classified as transmissible spongiform encephalopathies (TSE). It is later pass to cow, through meat and bone meal that contained scrapie-infected sheep product. This disease is now known as bovine spongiform encephalitis (BSE also known as mad cow). Then it passed to man when we eat BSE infected beef or mutton and this diease is know as Creutzfeldt-Jakob disease in human.

Jiani