Enveloped Viruses

Enveloped Viruses

	Enveloped Viruses Some icosahedral and helical animal viruses are surrounded by a membranous envelope l00-150A thick. An external envelope is also present in some plant viruses and bacteriophage. Enveloped ssRNA viruses Togaviruses Rhabdoviruses Paramyxoviruses Orthomyxoviruses Retroviruses Bunyaviruses Corona viruses Arenaviruses
Enveloped dsRNA viruses Bacteriophage φ96 Enveloped dsDNA viruses Bacteriophage PM2 Herpesviruses (nuclear assembly) Poxviruses (cytoplasmic assembly) Iridescent insect viruses e.g. TIV
The ssRNA viruses replicate in the cytoplasm of the host cell and are released from the cell by budding through the plasma membrane. They thus become surrounded by a part of the host cell membrane, which forms the envelope. The envelope resembles the typical biological membrane in consisting of a phospholipid bilayer in which are embedded proteill8. It has spikes which are composed of glycoproteins. The spikes may have haemagglutinating and/or neuraminidase activities. In the paramyxoviruses the haemagglutinating and neuraminidase activities are contained in the same glycoprotein.
In the orthomyxoviruses the two activities are contained in separate glycoproteins. Removal of the spikes with proteolytic enzymes or treatment with antiglycoprotein serum renders the virus particles non-infectious. It has been suggested that in togaviruses and orthomyxoviruses the glycoproteins have icosahedral symmetry. In rhabdomyxoviruses, paramyxoviruses and orthomyxoviruses, a protein is present internal to the lipid bilayer. This protein has been called the M-protein ('matrix' or 'membrane' protein). Its function may be to stabilize the lipid bilayer by providing a rigid framework.
	In four unrelated virus groups the lipid bilayer is not derived from the host cell membranes, but appears to be assembled de novo. These non-budding lipid containing viruses include (i) the dsDNA bacteriophage PM2, (ii) the dsRNA bacteriophage 96, (iii) the iridescent dsDNA insect viruses and (iv) the poxviruses. PM2 is the only lipid containing virus that does not contain glycoproteins.

Home | Site map | Submit Article | Resources | Search