The key difference between virion and viroid is their composition and complexity. Virions are complete virus particles with a nucleic acid genome surrounded by a protein capsid, while viroids are smaller, simpler infectious agents consisting of a circular RNA molecule without a protein coat.
What is Virion?
A virion is a complete, infectious particle of a virus. It is the extracellular form of a virus that can exist outside of a host cell and is capable of infecting other cells to replicate and cause infection. The virion is composed of a nucleic acid genome, which can be either DNA or RNA, surrounded by a protective protein coat called the capsid.
Some viruses may also have an outer envelope derived from the host cell membrane. The virion is the basic unit of viral structure and is responsible for transmitting viral genetic material from one host cell to another.
What is Viroid?
A viroid is a small, infectious, non-coding RNA molecule that causes disease in plants. Unlike typical viruses, viroids lack a protein coat and are composed solely of a short, single-stranded RNA molecule.
They are much simpler in structure and organization compared to viruses. Viroid is known to infect a wide range of plant species, causing various symptoms such as stunted growth, leaf distortion, and reduced yield.
Virion vs Viroid
The basic difference between virion and viroid is given below:
| Aspect | Virion | Viroid |
| Definition | A complete virus particle. | A small, circular RNA molecule. |
| Structure | Consists of nucleic acid (DNA or RNA) surrounded by a protein coat (capsid). | Consists only of single-stranded RNA. |
| Size | Larger in size, typically ranging from 20 nm to 400 nm. | Smaller in size, usually around 250 to 400 nucleotides. |
| Biological Function | Capable of infecting host cells and replicating within them. | Unable to replicate on their own and depend on host cellular machinery for replication. |
| Disease Association | Virions can cause various diseases in animals, plants, and humans. | Viroids are primarily associated with plant diseases. |