Give a brief account of viruses with respect to their structure and nature of genetic material. Also,name four common viral diseases.

(N/A) Viruses are sub-microscopic infectious agents that can infect all living organisms. $A$ virus consists of genetic material surrounded by a protein coat called a capsid.
The genetic material may be present in the form of $DNA$ or $RNA$.
Most plant viruses have single-stranded $RNA$ as their genetic material. Viruses infecting animals may have single or double-stranded $RNA$ or double-stranded $DNA$.
Bacteriophages,which are viruses that infect bacteria,usually possess double-stranded $DNA$. The protein coat (capsid) is made up of small subunits called capsomeres,which are arranged in helical or polyhedral geometric forms.
$AIDS$,smallpox,mumps,and influenza are four common examples of viral diseases.