Name the agent: (a) a small infectious RNA with no coat at all, which stunts potato plants and…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Name the agent:
- (a) a small infectious RNA with no coat at all, which stunts potato plants and makes their tubers long and thin
- (b) a misfolded protein with no nucleic acid, which damages the brains of cattle
- (c) a coat of protein with a strand of DNA inside, which bursts the bacteria it enters
Need a reminder? The key ideaShow
Viruses, viroids and prions are not in the five kingdoms. A virus is an obligate parasite: DNA or RNA, never both, inside a protein capsid. Ivanowsky (1892) found that the cause of tobacco mosaic passed through a bacterial filter; Beijerinck (1898) called it Contagium vivum fluidum; Stanley (1935) crystallised the virus. Diener (1971) found the viroid, free RNA with no coat. A prion is an abnormally folded protein (BSE, CJD).
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
(a) Free RNA with no coat: a viroid (potato spindle tuber disease).
(b) A misfolded protein: a prion (bovine spongiform encephalopathy).
(c) DNA in a protein coat that infects bacteria: a virus, a bacteriophage.
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