= Viral envelope
A <viral envelope> is a lipid membrane surrounding the internal structures of some <virus> particles. It contains host-derived <lipids> together with viral <membrane proteins>, often <glycoproteins>. It is structurally distinct from a <capsid>, the protein-based packaging associated with the viral <genome>.<Orthomyxoviridae report by the International Committee on Taxonomy of Viruses>[Virion and Fig. 1, lipid membrane and internal components]{ref}
Formation of the envelope connects viral assembly to the organization of a host <biological cell>. In a 1978 experiment with polarized <epithelial cells>, influenza particles emerged from the free apical surface, whereas <vesicular stomatitis virus> acquired its envelope at the basolateral membrane. The same cellular setting therefore supported different sites of <viral budding> for different viruses.<Asymmetric budding of viruses in epithelial monlayers: a model system for study of epithelial polarity by E. Rodriguez Boulan and D. D. Sabatini>[Abstract, contrasting membrane surfaces]{ref}
This observation makes the envelope a useful probe of membrane organization. Its host-derived material does not mean it is an arbitrary piece of unchanged host membrane: the completed particle has an organized set of viral components. Identifying where budding occurs and identifying which components enter the particle are related but different experimental questions.
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