LM11-2 - 1 Viruses (including phage), viroids and prions...

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Unformatted text preview: 1 Viruses (including phage), viroids and prions Overview All are non-cellular agents that infect host cells Each type of cell has its own specific viruses Viruses are very abundant (>10 6 /ml in sea water) Viruses contain NA (RNA or DNA, DS or SS) and proteins (capsid components , needed enzymes) Some viruses have envelopes derived from the CM of the infected host cell Viruses are classified into groups and families based on component differences Viroids only contain RNA and infect plant cells Virusoids only contain RNA and infect animal cells, require a helper virus Prions only contain amino acids and infect animals Viral varieties (Fig. 5.2) Sizes vary considerably, but all are visualized only with the use of an electron microscope Bacteriophage (phage) are viruses that infect prokaryotic cells Many phage are larger and more complex than viruses Capsids enclose the viral genome and are made of self-assembling protomers (subunits) Nucleocapsid is capsid plus genomic material 2 How viruses are classified 3 This system classifies viruses based primarily on the type of NA used for the genomic material +RNA viruses have ssRNA that serves as an mRNA - RNA viruses have ssRNA that is the compliment of an mRNA, therefore must be replicated before it can be translated into viral proteins Group 6 are retroviruses ssRNA is converted to dsDNA that is inserted into the host chromosome How viruses are classified (Tables 24.2, 24.1) 4 Other classification schemes use genome composition plus capsid characteristics, presence/absence of an envelope, and host range to assign viruses to families Types of capsids: helical (Figs. 5.3, 5.4) Capsids of helical (filamentous) viruses/phage are as large as NA; protomers bind to NA (Top): TMV (tobacco mosaic virus) (Bottom): Influenza virus is a helical virus with an envelope 5 Types of capsids: Polyhedral/icosahedral (Fig. 5.5) Polyhedral viruses (geodesic dome shape) vary from 60- 1500 capsomers (most common is icosahedral, with 20 sides/faces, 60 capsomers) Each capsomer is made of 3-6 protomers (a) polyoma virus (72 capsomers) (b,c) adenovirus (252 capsomers) 6 Complex viral structures (Figs. 5.7, 5.8)Complex viral structures (Figs....
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LM11-2 - 1 Viruses (including phage), viroids and prions...

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