Virus

Introduction to Virus

The word “Virus” originates from Latin word “Venom” which means “poison”. Virus was discovered by Ivanowsky in 1892. He said that viruses can be transmitted from infectious organism to a healthy organism The name of the first discovered virus was “Tobacco Mosaic Virus (TMV)” which caused Tobacco Mosaic Disease (TMD) in plants causing leaves to be wrinkled and mottled. 

It was generally believed that these viruses or poisons, were carried in the air cause many unexplained diseases. The study of viruses is called virology. 

Characteristics of all viruses

Viruses are the non-cellular infectious agents. They replicates only inside the living cells of an organism. They cannot live and reproduce outside of living cells since they lack the machinery to do so by themselves. They infect all kind of organisms like, animals and plants. They have a protein coat and a nucleic acid core. They range in size from 20 nm to 250 nm. They are smaller than most cells.

Viruses are either virulent, destroying the cell in which they are present, or becoming integrated into their host genome and remaining stable there for long time. They lack genes and enzymes necessary for energy production. Thus, they depend on host cell ribosomes, enzymes, and nutrients for protein production.

They are Obligate intracellular parasites which means that they cannot live and replicate outside of their living host cell. They possess either DNA or RNA, they never possess both. Their replication is directed by viral nucleic acid within a cell.

Structure of Viruses

Viruses may consist of viral genomes, Capsids, envelopes and tail fibres. The simplest viruses are consisting of only viral genome and capsid.