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prion1

[prahy-on] /ˈpraɪ ɒn/
noun
1.
any of several petrels of the genus Pachyptila, located in the oceans of the Southern Hemisphere and having serrated edges on the bill.
Origin
1840-1850
1840-50; < Neo-Latin < Greek príōn a saw

prion2

[pree-on, prahy‐] /ˈpri ɒn, ˈpraɪ‐/
noun
1.
a tiny proteinaceous particle, likened to viruses and viroids, but having no genetic component, thought to be an infectious agent in bovine spongiform encephalopathy, Creutzfeldt-Jakob disease, and similar encephalopathies.
Origin
1980-85; pr(oteinaceous) + i(nfectious) + -on1
Dictionary.com Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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British Dictionary definitions for prion

prion1

/ˈpraɪən/
noun
1.
any of various dovelike petrels of the genus Pachyptila of the southern oceans that have a serrated bill
Word Origin
C19: New Latin, from Greek priōn a saw

prion2

/ˈpriːɒn/
noun
1.
a protein in the brain, an abnormal form of which is thought to be the transmissable agent responsible for certain spongiform encephalopathies, such as BSE, scrapie, Creutzfeldt-Jakob disease, and kuru
Word Origin
C20: altered from pro(teinaceous) in(fectious particle)
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012
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Word Origin and History for prion
n.

petrel-like bird, 1848, from Greek prion "a saw," related to priein, prizein "to saw, to be cut in pieces." So called for its bill.

Online Etymology Dictionary, © 2010 Douglas Harper
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prion in Medicine

prion pri·on (prē'ŏn)
n.
A microscopic protein particle similar to a virus but lacking nucleic acid, possibly the infectious agent responsible for scrapie and other degenerative diseases of the nervous system.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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prion in Science
prion
  (prē'ŏn)   
A particle of protein that is thought to be able to self-replicate and to be the agent of infection in a variety of diseases of the nervous system, such as mad cow disease. Prion replication (in which strings of amino acids are reproduced) stands as an exception to a central tenet of biology stating that only nucleic acids, such as DNA, can self-replicate. The mechanism of prion replication is not clearly understood.

Our Living Language  : In 1997 Stanley Pruisner was awarded the Nobel Prize for physiology or medicine for his theory that a deviant form of a harmless protein could be an infectious agent, a transmitter of disease. Named prions (short for proteinaceous infectious particle), these misshapen proteins cause healthy proteins to misfold, fatally clumping together in the brain. Unlike other disease-causing agents, prions lack genetic material (DNA and RNA). Neurodegenerative prion diseases are often called spongiform encephalopathies because they leave the brain riddled with holes like a sponge. In animals, prion diseases include scrapie in sheep and bovine spongiform encephalopathy, commonly known as mad cow disease in cattle. In humans, diseases such as kuru and Creutzfeldt-Jakob disease (CJD) are also thought to be caused by prions. All the diseases are characterized by loss of motor control, dementia, paralysis, and eventual death due to massive destruction of brain tissue. Humans are thought to contract prion disease most commonly by eating prion-contaminated flesh. Kuru, a rare and fatal brain disorder, brought prion disease to the forefront. First described in the 1950s, kuru was most common among the Fore people of Papua New Guinea, who had a custom of eating the brains of their dead during funeral feasts. It is speculated that a tribe member developed CJD, his or her contaminated brain tissue was ingested, and the disease spread. Kuru reached epidemic levels in the 1960s, but the disease declined after the government discouraged the practice of cannibalism and now it has almost completely disappeared.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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prion in Culture
prion [(pree-on)]

A protein that not only folds into an unusual shape itself, but also seems to have the ability to cause other proteins to change their shape as well. For a long time, scientists were skeptical that prions existed, but now most accept them.

Note: Prions are thought to be the cause of mad cow disease.
The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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