define viroids and prions?
Answers
Answer:
Viroids are small plant pathogens that do not encode proteins.
Prions are infectious particles that contain no nucleic acids.
Viroids
Viroids are plant pathogens: small, single-stranded, circular RNA particles that are much simpler than a virus. They do not have a capsid or outer envelope, but, as with viruses, can reproduce only within a host cell. Viroids do not, however, manufacture any proteins. They produce only a single, specific RNA molecule. Human diseases caused by viroids have yet to be identified.
Viroid-infected plants are responsible for crop failures and the loss of millions of dollars in agricultural revenue each year. Some of the plants they infect include potatoes, cucumbers, tomatoes, chrysanthemums, avocados, and coconut palms.
Prions
Prions, so-called because they are proteinaceous, are infectious particles, smaller than viruses, that contain no nucleic acids (neither DNA nor RNA). Historically, the idea of an infectious agent that did not use nucleic acids was considered impossible, but pioneering work by Nobel Prize-winning biologist Stanley Prusiner has convinced the majority of biologists that such agents do indeed exist.
Key points :-
- The prion appears to be the first infectious agent found whose transmission is not reliant upon genes made of DNA or RNA.
- An infectious structural variant of a normal cellular protein called PrP (prion protein) is known to cause spongiform encephalopathies.
- Prions have been implicated in fatal neurodegenerative diseases, such as kuru in humans and bovine spongiform encephalopathy (BSE) in cattle.
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