What are Viroids?
Viroids are much simpler than viruses. Structurally, viroids are smaller in size, comprising single-stranded, circular RNA molecules having approximately 250-370 nucleotides. Viroids cannot replicate on their own, as their RNA does not encode any gene products. Unlike viruses, these viroids do not have a protein coat. They are just RNA particles.
These pathogens cause several infectious diseases in both plants and animals. In plants, viroid infections result in severe mechanical damage to plants.
Some diseases that are caused by the infection of viroids in plants are chrysanthemum stunt, citrus exocortis, cucumber pale fruit, etc.
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What are Prions?
Prions are infectious agents, which are responsible for several neurodegenerative diseases in mammals. These infectious agents are primarily composed of sialoglycoprotein – a combination of sialic acid and glycoprotein and usually lack nucleic acid.
Stanley Prusiner, an American neurobiologist proposed that the prions are infectious proteins. Based on his discoveries, he also proposed that they were responsible for the cause of scrapie. Scrapie is a type of neurological disease, affecting the nervous systems of animals, especially sheep and goats. Later, he coined the term prion for proteinaceous infectious.
In both humans and animals, these infectious agents cause a variety of neurodegenerative diseases and are mainly caused due to the abnormal folding of the proteins in the brain.
In humans, Creutzfeldt-Jakob disease, Fatal familial insomnia, Dementia are a few examples of diseases caused by prions.
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Let’s learn the differences between viroids and prions.
Viroids and Prions- Comparisons
| Definition | |
| Viroids are infectious RNA molecules. | Prions are infectious protein particles. |
| Size | |
| Viroids are smaller than viruses. | Prions are smaller than the viroids. |
| Composed of | |
| Viroids are composed of single strands of RNA. | Prions are composed of only protein molecules. |
| Nucleic Acid | |
| Present | Absent |
| Protein Components | |
| Absent | Present |
| Infections | |
| Viroids infect mostly plants. | Prions mainly cause neurodegenerative diseases. |
| Type of Diseases | |
| Citrus exocytic Tomato apical stunt Potato spindle tuber Grapevine yellow speckle Chrysanthemum stunt disease |
Mad cow diseases in cattle Scrapie in sheep and goats Creutzfeldt-Jakob disease in humans Gerstmann-Straussler- syndrome in humans |
| Treatment / Cure | |
| Traditional antiviroid methods have been employed for treating the infections caused by these viroids. | Currently, there is no treatment or cure for neurodegenerative diseases because prions are extremely difficult to destroy as they are resistant to chemicals, heat, radiation and even standard sterilisation procedures. |
Also Refer: Difference Between Virus And Bacteria
This article concludes the introduction to viroids and prions and their differences.
Stay tuned to BYJU’S Biology to learn more in detail about the different types of microbes, pathogens and the list of infectious diseases, along with their causes, symptoms, and their treatments.
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