Classification of Viruses
Viruses may be classified according to the type of the host, genetic material and number of strands. they are fallows
On the basis of Host
I) Animal Viruses
They live inside animal cells including man on entering the cell these disturb the metabolism of the host cell and cause various diseases.
Examples: Small pox viruses, polio virus, influenza virus
Animal viruses may enter cells by attaching to the surface. Inside the host cell they may multiply and form numerous new viral particles. Usually, animals viruses release from the host cells by the rupturing and subsequent death of the host cells.
II) Plant Viruses
They are parasites of plant cells, their genetic material is RNA which remains enclosed in the protein coat. The most important plant viruses are TMV, Potato Virus(PV) etc.
III) Bacterial Viruses
They are parasitic on bacteria and so also called bacteriophages. There are many varieties of bacteriophages their size and shape varies from species to species. Some phages are spherical, some comma shaped where as majority of them have tadpole like appearance.
On the basis of nucleic acids
I) DNA Viruses
These viruses posses DNA as the genetic material. On replication this DNA produces new DNA transmits information for protein synthesis through RNA.
II) RNA Viruses
These viruses posses RNA as the genetic material the RNA replicates directly to produce new RNA. Information for protein synthesis passes from RNA to protein without involvement of DNA.
III) DNA-RNA Viruses
In a group RNA tumor viruses called leuko viruses the genetic material is alternately DNA and RNA. In addition to the normal mode of transfer found in DNA viruses(RNA-DNA-RNA-PROTEIN).
With respect to number of strands in viruses
I) Double Stranded DNA
Double stranded DNA has been reported in pox viruses, bacteriophages. etc.
II) Single Stranded DNA
Single stranded DNA is found in the bacteriophages m-13.
III) Double Stranded RNA
Double stranded RNA has been found within viral capsid in the reoviruses of animals and in wound tumor viruses.
IV) Single Stranded RNA
Single stranded RNA is found in most of RNA viruses.
Example: TMV