Berkeley MCELLBI 140 - Prions (7 pages)

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Prions



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Prions

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Pages:
7
School:
University of California, Berkeley
Course:
Mcellbi 140 - General Genetics
General Genetics Documents

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Prions Other molecules besides organelle DNA are inherited in non Mendelian patterns Examples of non Mendelian patterns of inheritance extend beyond the inheritance of organelle DNA Certain DNA and RNA plasmids for example are inherited in non Mendelian patterns but the strangest cases of non Mendelian inheritance is the inheritance of endogenous proteins with altered structures these proteins are known as prions Prions can be inherited in yeast and the filamentous fungus Podospera anserina and most of our discussion will focus on two elements in yeast known as URE3 and PSI Prions were first proposed to cause spongiform encephalopathies in mammals Prions were first discovered as the etiological agents in transmissible spongiform encephalopathies such as scrapie in sheep and goats bovine spongiform encephalopathy BSE or mad cow disease in cattle and Creutzfeldt Jacob disease CJD Gerstmann Straussler Schneinker syndrome GSS fatal familial insomnia and kuru in humans Collectively these diseases have been explained by the prion hypothesis This hypothesis posits that the infectious agent is an abnormal form of a cellular protein known as PrP During the course of the prion disease a protease resistant aggregated form of PrP designated PrPSc accumulates in the brain The model proposes that the presence of PrPSc which has the same sequence as PrP but a different structure will recruit normal PrP into the abnormal structure to spread the disease The disease is thought to spread when animals are fed food containing brain material Alternatively with rare genetic forms of the disease individuals inherit a mutant form of PrP that has a higher probability of spontaneously folding into a protease resistant prion form In 1997 Stanley Prusiner a neurologist at UCSF won the Nobel Prize in Physiology and Medicine for his work leading to the prion hypothesis Below are several results for this class of diseases that are consistent with the prion hypothesis 1 No nucleic acid has ever



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