Difference Between Viroids and Prions

Main Difference

The main difference between viroids and prions is that viroids are small pathogens of plants that do not encode proteins, whereas prions are infectious particles that have no nucleic acid.

Viroids vs. Prions

Viroids are naked infectious, small RNA molecules while prions are infection producing protein particles that cause neurological degenerative diseases in animals and humans. Viroids are of small stranded circular RNA whereas prions formed of only protein particles. A protein coat is absent in viroids like all other viruses; on the other hand, RNA or DNA is absent in prions. Viroids are inactivated by ribonuclease digestion but resilient to trypsin digestion and proteinase K; on the contrary, prions are inactivated by trypsin digestion and proteinase K but resilient to ribonuclease digestion. Viroids are smaller in size than viruses; on the flip side, prions are mostly smaller than viroids. Viroids infect only higher plants (except hepatitis D virus in humans that is similar to viroids); conversely, prions infect humans and animals causing neurological degenerative diseases. Diseases caused by viroids are chrysanthemum stunt disease, potato spindle tuber disease, whereas diseases caused by prions in humans and animals are scrapie disease in sheep and goat, mad cow disease in the cow.

Comparison Chart

ViroidsPrions
Viroids are covalently closed, having low molecular weight, circular, single-structure RNA molecule that multiply in plants and caused diseases.Prions are small, infectious protein particles that have no nucleic acid means no replication, enter in humans and caused diseases.
Structure
Small stranded circular RNAFormed of only protein particles
Absence Of
Protein coat is absentRNA or DNA is absent
Inactivated By
Ribonuclease digestionTrypsin digestion and proteinase K
Resistant To
Trypsin digestion and proteinase KRibonuclease digestion
Size
Smaller in size than virusesMostly smaller than viroids
Infections
Infects only higher plants (except hepatitis D virus in humans that is similar to viroids)Infect humans and animals causing neurological degenerative diseases
Diseases
Chrysanthemum stunt disease, potato spindle tuber diseaseScrapie disease in sheep and goat, mad cow disease in the cow.

What are Viroids?

Viroids are covalently closed, having low molecular weight, circular, single-structure RNA molecule that multiply in plants and caused diseases. Viroids are virus without the protein coat means an incomplete virus. Having no protein coat means less protection against the immune system. So, it will be suicidal for viroids to attack humans or animals. It only affects higher plants (except hepatitis D virus in humans that is similar to viroids). Viroids consist of a very short stretch of circular, single-stranded RNA without the protein coat. They are a strand of naked RNA. Viroids are smaller in size than viruses. The so far discovered smallest viroid is 220 nucleotides long. Any known protein does not code for RNA of viroids. Viroid’s RNA affects a plant chemical machinery to produce essential proteins for it. Pollens or seeds in plants usually transmit viroids. When an infected pant rub against an uninfected plant, the insects like butterflies which feed on different plants, spread the viroids around the whole crop field. Identified species of viroids are about 33. Viroids affect crops like potatoes, tomatoes, cucumbers, chrysanthemums, avocados, coconut palms, and fruit trees. They don’t cause diseases in humans, but they can cause crop failure, which means each year a huge loss of agriculture revenue and a million dollars. Diseases caused by viroids are chrysanthemum stunt disease, potato spindle tuber disease.

What are Prions?

Prions are small, infectious protein particles that have no nucleic acid means no replication, enter in humans and caused diseases. Prions transmuted proteins, which are undetectable because they are part of the host’s bio machinery. They are most dangerous of all, capable of killing the host, with no immune system response. Prions, short for proteinaceous infectious particles, made up of only protein. Prions do not consist of DNA or RNA to transmit infection. Prions are an abnormal form of harmless proteins. Once prions enter the brain through different conditions, they force the normal cellular proteins of the brain to begin folding into abnormal shapes. This abnormality destroys the neurons and eventually leads the brain to become riddled with holes. Prions cause several diseases in humans and animals, including scrapie in sheep, kuru and Creutzfeldt Jakob disease(CJK) in humans, bovine spongiform encephalopathy(BSE) in cattle, and chronic wasting disease(CWD) in elk and deer. All these known diseases of prions affect the structure of the brain or other nervous tissues, and all of them are fatal and untreatable. Prions cannot stop by cooking or sterilization. Prions are resilient radiation, chemicals, and heat. So, they are almost unstoppable. The best ways to stop spreading prions in animals and humans is to prevent brain tissue from getting into the food supply or onto medical equipment or denatured the protein structure.

Key Differences

  1. Viroids are naked infectious, small RNA molecules while prions are infectious producing protein particles that cause neurological degenerative diseases in animals and humans.
  2. Viroids are of small stranded circular RNA whereas prions formed of only protein particles.
  3. A protein coat is absent in viroids; on the other hand, RNA or DNA is absent in prions.
  4. Viroids are inactivated by ribonuclease digestion but resilient to trypsin digestion and proteinase K; on the contrary, prions are inactivated by trypsin digestion and proteinase K but resilient to ribonuclease digestion.
  5. Viroids are smaller in size than viruses; on the flip side, prions are mostly smaller than viroids.
  6. Viroids infect only higher plants (except hepatitis D virus in humans that is similar to viroids); conversely, prions infect humans and animals causing neurological degenerative diseases.
  7. Diseases caused by viroids are chrysanthemum stunt disease, potato spindle tuber disease, whereas diseases caused by prions in humans and animals are scrapie disease in sheep and goat, mad cow disease in the cow.

Conclusion

Above discussion concludes that viroids are naked infectious, small RNA molecules while prions are infection producing protein particles that cause neurological degenerative diseases in animals and humans.

Janet White

Janet White is a writer and blogger for Difference Wiki since 2015. She has a master's degree in science and medical journalism from Boston University. Apart from work, she enjoys exercising, reading, and spending time with her friends and family. Connect with her on Twitter @Janet__White

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