Prions (misfolded proteins) and viroids (single-stranded RNA particles) are pathogens that are smaller than viruses.
Prions and viroids are called subviral because they are smaller than viruses.
Prions are proteins with a defective structure that also trigger other proteins to adopt this faulty structure. Prions have no genetic material at all. Prions are responsible for a variety of different neural diseases.
Viroids are plant pathogens that consist of a small, circular, single-stranded RNA particle. 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. Human diseases caused by viroids have yet to be identified.
Practice Questions
Khan Academy
MCAT Official Prep (AAMC)
Practice Exam 2 B/B Section Question 28
Key Points
• Subviral particles are named as such because they are smaller than viruses.
• Prions are defective proteins that cause other proteins also to misfold, causing disease.
• Viroids are small, single-stranded RNA particles that cause disease in plants.
Key Terms
prion: a self-propagating misfolded, pathogenic form of a protein
viroid: plant pathogens that consist of a small, single-stranded RNA particle, but without the protein coat typical of viruses
subviral: because they are smaller than viruses
RNA: Ribonucleic acid is a single-stranded molecule made up of nucleic acids
capsid: the protein shell of a virus
