viroids

[Aakanksha]

How are viroids different from viruses?

[ahwriter]

Answer

Viroids were discovered in 1917 by T.O. Denier. They cause potato spindle tuber disease. They are smaller in size than viruses. They also lack the protein coat and contain free RNA of low molecular weight.

[Aakanksha]

Viroids and viruses are both infectious agents that can cause diseases in plants, animals, and even humans, but they differ in several key ways:

1. Nature and Structure:

   • Viroids: Viroids are small, circular RNA molecules that lack a protein coat (capsid) or any other surrounding membrane. They consist solely of a short, single-stranded RNA molecule, usually a few hundred nucleotides long.
   • Viruses: Viruses are much more complex. They consist of genetic material (either DNA or RNA) surrounded by a protein coat called a capsid. Some viruses also have an outer lipid envelope derived from the host cell membrane.

2. Genetic Material:

   • Viroids: Viroids contain only RNA as their genetic material.
   • Viruses: Viruses can contain either RNA or DNA as their genetic material. DNA viruses have double-stranded DNA, while RNA viruses can have single-stranded or double-stranded RNA.

3. Protein Coat (Capsid):

   • Viroids: Viroids lack a protein coat or capsid.
   • Viruses: Viruses have a protein coat (capsid) that protects their genetic material.

4. Replication:

   • Viroids: Viroids replicate in host cells by using the host’s cellular machinery. They do not code for their own proteins and rely on the host cell’s enzymes for replication.
   • Viruses: Viruses also replicate within host cells, but they often encode their own replication machinery, including enzymes and proteins necessary for the viral life cycle.

5. Host Range:

   • Viroids: Viroids primarily infect plants. They are responsible for causing various plant diseases by interfering with the normal cellular processes of the host plant.
   • Viruses: Viruses can infect a wide range of hosts, including plants, animals, fungi, bacteria, and archaea.

6. Transmission:

   • Viroids: Viroids are usually transmitted through plant propagation processes, such as when infected plant parts are used to grow new plants.
   • Viruses: Viruses can be transmitted through various means, including direct contact, airborne particles, contaminated water, and insect vectors.

7. Pathogenesis:

   • Viroids: Viroids cause diseases in plants by disrupting normal cellular processes and interfering with gene expression.
   • Viruses: Viruses cause diseases by hijacking host cells’ machinery to replicate themselves, often damaging or destroying host cells in the process.

8. Treatment:

   • Viroids: There are no specific antiviral treatments for viroid infections. Management typically involves controlling the spread of infected plants and using disease-resistant varieties.
   • Viruses: Antiviral treatments and vaccines can be developed for certain viral infections, although their effectiveness varies widely.

In summary, viroids are simpler infectious agents composed solely of RNA, lacking a protein coat, and primarily affecting plants. Viruses are more complex, with either RNA or DNA as their genetic material, a protein coat, and a broader host range that includes plants, animals, and other organisms.

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