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Part III Virology A-prof. Yang Haibo Dept. of medical Microbiology and immunology virus • • • • The smallest infectious agents Contain only one kind of nucleic acid Non-cellural type Replicate only in living and susceptible cells Section 1 size and shape of viruses Size of viruses • Measuring unit: nanometer, nm • A small virus has a diameter of about 20nm. Parvovirus 细小病毒组 • A large virus have a diameter of up to 400nm. Poxviruses 痘病毒类 Size and Shape of Viruses 衣原体 立克次体 390nm 450nm 65×95nm 15×300nm 噬菌体 烟草花叶病毒 葡萄球菌 1000nm 70nm 痘苗病毒 300×250nm 腺病毒 100nm 流感病毒 10nm 30nm 脊灰病毒 40nm 乙脑病毒 卵白蛋白 Shapes of viruses • • • • • • Spherical Rod-shaped Brick-shaped Tadpole-shaped Bullet-shaped Filament White, DO and Fenner, FJ. Medical Virology, 4th Ed. 1994 Shapes of Viruses:Spherical Shapes of Viruses :Rod-shaped Shapes of Viruses :Brick-shaped . Tadpole-shaped Shapes of Viruses :Bullet-shaped Shapes of Viruses :Filament Section 2 structure and function of viruses Terms and definitions in virology virion: the complete virus particle capsid: the protein shell, or coat, that encloses the nucleic acid genome envelope: a lipid-containing membrane that surrounds some virus particles Virion envelope Capsid Viral core Structure of virion peplomer (spike) viral core capsid nucleocapsid (Naked virus) nucleic acid capsomere Enveloped virus envelope Terms and definitions in virology • Capsomeres: morphologic units, clusters of polypeptedes • Nucleocapsid: the protein-nucleic acid complex • Naked virus • Enveloped virus 1. Viral protein • • • • • Protect the viral genome Attach to susceptible cell Structural symmetry of the virus Antigenic Enzymes (non-structral proteins) 2. Viral nucleic acid • In the center of the virion, Control the viral heredity and variation, responsible for the infectivity. • The genome of a virus can be either DNA or RNA 3. Viral lipid envelopes • A lipid-containing membrane that surrounds some viral particles. • acquired while the viral nucleocapsid buds through a cellular membrane in the course of maturation Release Budding through plasma membrane (enveloped virus) Rupture(un-enveloped virus) 3. Vidral lipid envelopes • Viruses-encoded glycoproteins are exposed on the surface of the envelope. • Not all viruses have the envelope, and viruses can be divided into 2 kinds: enveloped virus and naked virus. 4. Viral glycoproteins • virus-encoded • Interact with a cellular receptor • Important viral antigens Section 3 structure of viral capsid symmetry • Cubic (Icosahedral 二十面体的) • Helical • Complex Icosahedral Helical Cubic symmetry • Be of the icosahedral pattern • Has 20 faces, each an equilateral triangle • 12 vertices 顶角 • The physical appearance of the particle is spherical Icosahedral symmetry • 20 faces • 12 vertices http://www.tulane.edu/~dmsander/WWW/Video/Video.html Icosahedral symmetry Helical symmetry • Protein subunits are bound in a periodic 循环的 way to the viral nucleic acid, winding it into a helix Tobacco mosaic virus adapted from: Klug and Caspar Adv. Virus Res. 7:225 Helical symmetry • Length controlled by nucleic acid • Helix may be stiff or flexible • All animal viruses with helical symmetry are enveloped Complex symmetry • Do not exhibit simple cubic or helical symmetry • More complicated in structure Complex symmetry Poxvirus family Atypical viruslike antigens Defective virus缺陷病毒P246 • A virus particle that is functionally deficient in some aspect of replication • • A virus consisted of Viral nucleic acid and protein but cannot replicate without a “helper” virus that provides missing function. Viroids 类病毒 • Small infectious agents that cause diseases of plants • Consist a single molecule of circular RNA without protein coat or envelope prions • Infection particles composed solely of protein with no detectable nucleic acid • Highly resistant to inactivation by heat, formaldehayde and UV Prions (protinaceous infection particle) prion protein,PrP Cellular PrP, The agent of TSEs--transmissible spongiform encephalopathy. Scrapie prion protein Prion disease • • • • • • CNS Long incubation Slow course of disease Spongiform encephalopathy Vacuolation 空泡形成 of neurons Rare in man Clinical findings： The first TSEs, 300 years ago, EU scrapie of sheep and goat bovine spongiform encephalopaty,BSE Kuru disease Creutzfeld-Jakob diaseae,CJD variant CJD, v-CJD Review questions 1. What are the two types of symmertry of viral capsid? 2. What are the functions of viral proteins? 3. What is the composition of the viral envelope, and how is it formed? 4. Which proteins of virus induce protective antibody? 5. What are the differences between viruses and prions?
