Definition and Characteristics of Virus
Definition of Virus:
Mathwas (1981) considers a virus as a set of one or more template molecules normally encased in a protective coat or coats of protein or lipoprotein, which is able to organize its own replication only within suitable host cells where its production is:
i) Dependent on hosts protein synthesizing machinery (ribosomes).
ii) Organised from pools of required material rather than binary fission and
iii) Located at sites which are not separated from the host cell contents by a lipoprotein bilayer membrane.
Bos (1983) defines virus as an infectious agent often causing disease, invisible with the light microscope ( Sub-microscopic) , small enough to pass through a bacterial filter, lacking a metabolism of its own and depending on a living host cell for multiplication. Viruses are small packages of host alien genetic information of one type. (RNA or DNA), either in one strand or in a few segment. Encapsulated together or separately and enclosed in a coat of one or more types of protein, some time with an extra coat (envelope) and some other constituents.
Characteristic of Virus:
Following characters will always be includes:
i) Viruses contain one or more pieces of a single type of nucleic acid, either RNA or DNA, never both.
ii) The nucleic acid carries the genome of the virus which differs from one virus to another.
iii) The genome in the nucleic acid strand directs the synthesis of specific proteins for the protein coat which must be present in all viruses throughout their active phase except at the time of replication when, protein coat and nucleic acid are separated.
iv) Viruses rely on living host cells for most of the enzymes necessary for their replication.
v) Viruses are in cable of growing for the synthesis of Lipman system is absent in Viruses.