Tell Viruses, Viroids and Prions Apart
Acellular infectious agents differ by genome, protein coat and host range.
Living-system questions are solved by matching a structure or organism to its function, process and stated condition.
Viruses carry a genome in a capsid
Viruses are obligate intracellular parasites. Their nucleic acid is DNA or RNA, enclosed by a protein capsid; bacteriophage genetic material lies in its head. Tobacco mosaic virus contains RNA, not DNA. Plant viral disease may cause mosaic patterns, leaf rolling and curling.
Viroids and prions are simpler
Viroids are short naked single-stranded RNA molecules that infect plants and have no protein coat. Prions are infectious misfolded proteins associated with diseases such as scrapie and Creutzfeldt–Jakob disease. Potato spindle-tuber disease is viroid-caused; wheat smut is fungal.
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- ✓Virus: DNA or RNA inside a capsid; intracellular replication.
- ✓Viroid: naked ssRNA, primarily plant pathogens.
- ✓Prion: infectious protein; not a nucleic-acid genome.
Do not swap viroid disease, prion disease and fungal disease examples.
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