VIRUS PROPERTIES • Infectious – must be transmissible horizontally • Intracellular – require living cells • RNA or DNA genome, not both* • Most all have protein coat* • May of may not have lipid envelope • May have broad or narrow host range • Replication involves eclipse (breaking apart of virus particles) and reassembly • Use host factors for to complete replication cycle
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VIRUS PROPERTIES Infectious – must be transmissible horizontally Intracellular – require living cells RNA or DNA genome, not both* Most all have protein.
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VIRUS PROPERTIES• Infectious – must be transmissible horizontally• Intracellular – require living cells• RNA or DNA genome, not both*• Most all have protein coat*• May of may not have lipid envelope• May have broad or narrow host range• Replication involves eclipse (breaking apart of
virus particles) and reassembly• Use host factors for to complete replication cycle
SOME CONSEQUENCES AND EFFECTS OF VIRUS INFECTION
• Like other life forms, viruses promote the propagation of their own kind
• Like other life forms, viruses evolve in response to selection pressure
• Viruses are major factors in promoting the evolution of higher organisms
• Viruses help control populations of their hosts, including humans
Virus-like agents classified and studied with viruses
• Viroids– No coat protein, no coding capacity
• Prions– No nucleic acid (?)
• Retrotransposons– No infectivity (?)
Host properties influence the virus types found in that host group
• Vertebrates have broad range of viruses
• Plants have mostly small RNA viruses
• Fungi have mostly dsRNA viruses
• Single-celled organisms have mostly large dsDNA viruses
Viruses aresubmicroscopic intracellular pathogens
Flint et al., 2004Principles of VirologyFig. 1.8
Sizes of microscopic and submicroscopic biological entities and their ability to be examined using various technologies
Viruses may be simple or complex
• Genome sizes 0.3 - 1200 kb; average genome sizes vary with host organism types
• Isometric particle sizes vary from ~24 nm to ~400 nm diameter
• May have single-stranded (ss) or double-stranded (ds) RNA or DNA genome
• If ssRNA, may be + or – sense
• May have one or many proteins in particles
• May or may not have lipid envelope
Types of viral genomes• double-stranded (ds) DNA
– Rarely segmented– Often large
• single-stranded (ss) DNA– Rarely large– Less common than dsDNA
• ssRNA, negative sense– Often found in viruses with broad host ranges
• ssRNA, positive sense– Most common overall
• dsRNA– Often segmented– Particle structure often critical
Composition of viruses infecting different hosts
• No “rules” about virus families that may or may not be present in a given kingdom
• Some types of viruses are found more commonly in some kingdoms than in others– Many plant viruses contain ssRNA genomes– Many fungal viruses contain dsRNA genomes– Many bacterial viruses contain dsDNA genomes
• Host properties determine the types of viruses that tend to be found in members of a biological “kingdom”