MCAT Content / Viral Life Cycle / Prions And Viroids Subviral Particles

Prions and viroids: subviral particles

Topic: Viral Life Cycle

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

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