Virus Structure:
Outside a host cell, virus is a crystalline structure, composed of protein. Inside the crystal, there is genetic material, which can be either RNA or DNA. No virus has both RNA and DNA. Viruses, infecting plants, have single-stranded RNA. Viruses, infecting animals, have either single or double-stranded RNA or double-stranded DNA.
The protein coat is called capsid. Capsid is made of smaller subunits, called capsomeres, it protects nucleic acid.
Diseases caused by Virus; AIDS, Mumps, Influenza, Herpes.