PART_18 FORMATION OF VIRUSES.These are formed from protein subunits called capsomeres. Viruses can have a lipid envelope derived from the host cell membrane. The capsid is made from proteins encoded by the viral genome and its shape serves as the basis for morphological distinction.Viruses may have arisen from mobile genetic elements that gained the ability to move between cells. They may be descendants of previously free-living organisms that adapted a parasitic replication strategy. Perhaps viruses existed before, and led to the evolution of, cellular life.