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Lec 36-Viruses.docx

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BIOL 1010
Igor Kovalchuk

Viruses Lecture 36 Virus classification  The seven groups used to classify viruses are then: o dsDNZ viruses o ssDNA viruses o dsDNA viruses o (+) ssRNA viruses o (-) ssRNA (influenza) viruses o RNA reverse transcribing viruses (AIDS, leukemia) o DNA reverse transcribing viruses Release from cell  Before the progeny virion actually exit the cell, their components of the virus must be assembled, forming the basic structure of the virus  Once the basic structure is formed, many viruses undergo changes to their structural proteins  These protein cleavages and rearrangements allow the virion more thermodynamically stable configurations as well as a better=product the viral genome  This process is generalized as maturation  Finally, the progeny can exit the host cell by lysine it or by budding Release from cell-Virion assembly  Assembly involves putting together all the components of the progeny virion, including the nucleic acid enclosed in the protective protein capsid  Molecular and cellular chaperones may be made by some viruses to aid in assembly of the viral components, although they do not contribute to the virus structure  Other viruses self-assemble, suggesting a lowest-energy confirugation of the assembled virion  Viruses disallow ambiguity during assembly by having symmetrical strucutres  The arrangement of protiens in the protective capsid are normally in repeating arrays of ordered protein(s)  The site of assembly also varies between viruses: o Some viruses assemble in the cytoplasm o Others assemble in the nucleus o Other on the inner surface fo the cell membrane Release from cell-maturaiton  Maturation is when the virus becomes infectious  Assembly and maturation occur simultaneously in some viruses, whearas other virus progeny mature after exiting the cell  Often, biochemical and structural changes occur during and following assembly which allow certain advantages to the virus for surviving  Cleaving certain proteins allow stable, protected configuration.  Enveloped viruses acquire their envelope during maturation  They always mature by passing through a membrane (not necessarily the plasma membrane) and obtain their envelope Release of Virus- Exit from cell  Most non-enveloped viruses exit the host cell via a lytic mechanism o The cell is disintegrated (viral structural proteins may inhibit cell metabolism) and the virus is released  Enveloped viruses but out through the cell membrane  Capsid proteins interact with the inner surface of the cell membrane, forcing the virus out of the cell  The cell may or not be killed by budding  During the process, the virus acquires a lipid membrane and envelope proteins, but also imparts new antigenicity to the cell by inserting viral glycoproteins in the cell membrane  The cell is targeted by the host immune system.  Still other viruses assemble in the nucleus o At the inner lamella of the nuclear membrane, the virus acquires its envelope and matures o Vesicles carry the
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