enveloped viruses contain a membrane surrounding the nucleocapsid (figure9.5) many viruses are enveloped , and most of these infect animal cells (for example, influenza virus), although occasional enveloped bacterial and plant viruses are also known. the viral envelope consists of a lipid bilayer with proteins, usually glycoproteins, embedded in it. the lipids of the viral membrane are derived from the membranes of the host cell, but viral membrane proteins that are encoded by viral genes are also embedded in the membrane. the symmetry of enveloped viruses is not expressed by the virion as a whole, but by the nucleocapsid present inside the virus envelope.