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Historical perspectives • TMD 1886 • Filterable agent 1892: Ivanowski • Isolation: 1935 Stanley Chapter opener 13 General characteristics • • • • • • Virus Life Cycle acellular Obligate intracellular parasite No independent metabolism No independent motility Infects bacteria, animals and plants Nucleic acid and protein • Extracellular: inert, infectious virion • Intracellular: active, replicating nucleic acid – Goal is reproduction Viral structures/terminology • • • • • • Virion Capsid: capsomeres Nucleic acid Nucleocapsid Envelope Naked vs. enveloped Table 13.1 1 Capsid (capsomeres) Genetic material of viruses • • • • dsDNA ssDNA dsRNA ssDNA Figure 13.1 - Overview Hosts of viruses Figure 13.2 Viral sizes TMV bacteriophages Budding influenzae virus HIV on wbc Figure 13.3 - Overview Figure 13.4 - Overview (1 of 4) Figure 13.4 (2 of 4) Figure 13.4 (3 of 4) 2 Viral shapes Figure 13.4 (4 of 4) Figure 13.5 - Overview helical Helical capsid TMV Figure 13.5a Polyhedral capsid Cold virus icosahedron http://www.rkm.com.au/VIRUS/Influenza/bird-flu-reassort.html http://www.rkm.com.au/VIRUS/ Figure 13.5b 3 Complex: smallpox Complex: rabies virus bullet shaped Figure 13.5c Complex virions Figure 13.5d bacteriophage Figure 13.8 - Overview enveloped Figure 13.7 - Overview 4 Viral Taxonomy • • • • Nucleic acid type Morphology: shape, size, envelope Strategy for replication Viral species (same genetic info) Table 13.2 (1 of 2) Viral LYTIC replication: T4 PHAGE Table 13.2 (2 of 2) Figure 13.8 - Overview (1 of 5) Figure 13.8 (2 of 5) Figure 13.8 (3 of 5) 5 Figure 13.8 (4 of 5) Figure 13.8 (5 of 5) Lysogeny (replication): bacteriophage lambda Figure 13.9 Figure 13.10 Animal virus replication: entry mechanisms Example of lysogenic conversion in bacteria? Figure 13.11 Figure 13.12 - Overview 6 Direct penetration Membrane fusion Figure 13.12a, steps 1-3 endocytosis Figure 13.12b, steps 1-5 Budding of virions from infected cell Figure 13.12c, steps 1-6 Figure 13.13 Replication strategies Viruses in cancer Example? Figure 13.15 - Overview (1 of 4) 7 Embryonated chick eggs Culturing bacteriophage on lawn of bacterial cells Figure 13.16 Figure 13.17 Cell culture Figure 13.18 Viroids: infectious RNA Potato spindle tuber viroid: PSTV Figure 13.19 Figure 13.20 8 Sprongiform encephalopathies: sheep brain scrapie Prion: proteinacious infective particles Prion protein: PrP Figure 13.21 Mad Cow Disease Figure 13.22 comparisons UN 13.2 Table 13.5 Discuss Avian Flu threat UN 13.1 UN 13.3 9