viroid, an infectious particle smaller than any of the known viruses, an agent of certain plant diseases. The particle consists only of an extremely small circular RNA (ribonucleic acid) molecule, lacking the protein coat of a virus.
What is the difference between a virus and a viroid?
Viruses and viroids are disease-causing organisms. The difference between virion (virus) and viroid is that viroid is a smaller form of a virus with RNA nucleic acid. In contrast, a virus can have either DNA or RNA.
Which disease is caused by viroids?
The only human disease known to be caused by a viroid is hepatitis D. This disease was previously ascribed to a defective virus called the delta agent. However, it now is known that the delta agent is a viroid enclosed in a hepatitis B virus capsid.
Are viroids bacteria?
Viruses can infect bacteria, Archaea, plants and animals, and cause diseases, such as rabies, smallpox, HIV and AIDS in humans, as well as tobacco ringspot in tobacco plants. Viroids, on the other hand, have an exclusively single-stranded RNA genome and have been shown to only cause infection in plants.
What are the viroids and prions?
Viroids consist of small, naked ssRNAs that cause diseases in plants. Virusoids are ssRNAs that require other helper viruses to establish an infection. Prions are proteinaceous infectious particles that cause transmissible spongiform encephalopathies. Prions are extremely resistant to chemicals, heat, and radiation.
Is a virion a virus?
The virion, that is the complete infectious virus particle, includes a genome comprising one or a few molecules of either DNA or RNA, surrounded by a morphologically defined protein coat, the capsid; the capsid and the enclosed nucleic acid together constitute the nucleocapsid.
How do viroids work?
Viroids replicate through an RNA-based rolling-circle mechanism with three steps that, with some variations, operate in the strands of both polarities: i) synthesis of longer-than-unit strands catalyzed by a host nuclear or chloroplastic RNA polymerase that reiteratively transcribes the initial circular template, ii)
How are viroids transmitted?
Viroids only infect plants, and infectious viroids can be transmitted to new plant hosts by aphids, by cross contamination following mechanical damage to plants as a result of horticultural or agricultural practices, or from plant to plant by leaf contact.
Do viroids have DNA?
All viroids have RNA as their genetic material. Moreover, viroids are entities which are smaller than viruses and affect only plants.
Who discovered viroids?
The pathogen is called a viroid by its discoverer, Dr. Theodor 0. Diener, to distinguish it from a virus.
What are characteristics of viroids?
Characteristic Features Of Viroids
Viroids contain only RNA. These are known to be smaller in size and infect only the plants. These are among the smallest known agents causing infectious disease. Viroids are the species of nucleic acid with relatively low molecular weight and a unique structure.
