Flint et al. All viruses are constructed according to certain basic principles. Viruses consist of nucleic acid and protein. The virus exists in a harsh environment, low pH, outside of the body in the dry atmosphere. Some viruses are resistant to detergents such as SDS, have to be broken open with urea.
Most viruses are resistant to proteolytic enzymes.
The envelope, which is derived from the host cell, is also a protective barrier. The information for recognition and interaction with host cell lies in the protein component. The site on the host cell to which the virus binds is known as the receptor, and is specific for different viruses. The site on the virus, which binds to the host cell, is the viral ligand. Quite often the proteins surrounding the virus have enzymatic activity essential for virus replication.