Viruses general characteristics

Viruses general characteristics

Virus 

Viruses are infectious agents having small size and simple composition. They can multiply only in living cells of plants, animals, or bacteria. This name “virus” is originated from a Latin word meaning poison or slimy liquid.

general characteristics of virus 

1. Viruses have a special taxonomic position. They are not animals, plants, or prokaryotic bacteria, and they are placed in their own kingdom. In fact, in the strictest sense, viruses should not be considered organisms, because they are not free-living i.e., they cannot replicate and carry-on metabolic processes without a host cell.
2.  All true viruses have nucleic acid either DNA or RNA and protein.  The nucleic acid encodes the genetic information distinct for each virus.
3.  The infective, extracellular form of a virus is known as the virion. It has at least one distinct protein synthesized by particular genes in the nucleic acid of that virus.
4. At least one of these proteins forms a shell around the nucleic acid known as capsid in virtually all viruses.
5. Some viruses also have other proteins which are present internal to the capsid. Some of these proteins work as enzymes, often during synthesis of viral nucleic acids. 
6. Viroids are disease-causing organisms that have no structural proteins and contain only nucleic acid.
7. Other virus like particles that are composed primarily of a protein tightly complexed with a small nucleic acid molecule are known as prions. 
8. Prions are very resistant to inactivation and appeared as a cause of degenerative brain disease in mammals, including humans. 
9. Viruses are essential parasites. They depend on the host cell for virtually all of their life-sustaining functions. They lack ribosomes that's why they cannot synthesize proteins .  Viruses use the ribosomes of their host cells to translate viral mRNA into viral proteins. They derive energy and all other metabolic functions from the host cell. 
10. The true infectious part of viruses is their nucleic acid, either DNA or RNA but never both.