Transcript viruses
viruses • Living • Nonliving • Contain a single type of nucleic acid (DNA or RNA), protein coat, sometimes an envelope. • Are obligatory intracellular parasites. Multiply by using host cell’s synthesizing machinery to cause the production of specialized elements that can transfer the nucleic acid to other cells. • Multiply inside living cells by using the synthesizing machinery of the cell. • Why does this make targeting viruses difficult? Host Range • The spectrum of host cells in which a virus can multiply. • Mot viruses infect only specific types of cells in one host species. • The host is determined by the specific attachment site on the host cell’s surface and the availability of host cellular factors. Virus Size Figure 13.1 Taxonomy of viruses • Currently based on type of nucleic acid, strategy for replication and morphology. • Virus family names end in –viridae; genus names end in –virus • A viral species is a group of viruses sharing the same genetic information and ecological niche Viral Taxonomy • Herpesviridae • Herpesvirus • Human herpes virus 1, HHV 2, HHV 3 • Flue H1N1 • Retroviridae • Lentivirus • Human Immunodeficiency Virus 1, HIV 2 Isolation, growth and identification • Must be grown on living cells. • Easiest to grow are bacteriophage, because bacteria are easy to grow. Growth results. • Plaques for bacteriophage. • Cytopathic effects on cell culture. Growing Viruses • Viruses must be grown in living cells. – Bacteriophages form plaques on a lawn of bacteria. Figure 13.6 Growing Viruses • Animal viruses may be grown in living animals or in embryonated eggs. Figure 13.7 Growing Viruses • Animal and plants viruses may be grown in cell culture. – Continuous cell lines may be maintained indefinitely. Figure 13.8 Identification. • Serological tests (Antibodies) • RFLP and PCR • (Discussion) Typical viral infection • • • • • Attachment Penetration Biosynthesis Maturation Release • Burst size and burst time Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber 1 Attachment: Phage attaches to host cell. Base plate Pin Cell wall Tail Plasma membrane 2 Penetration: Phage pnetrates host cell and injects its DNA. Sheath contracted Tail core 3 Merozoites released into bloodsteam from liver may infect new red blood cells Figure 13.10.1 Tail DNA 4 Maturation: Viral components are assembled into virions. Capsid 5 Release: Host cell lyses and new virions are released. Tail fibers Figure 13.10.2 One-step Growth Curve Figure 13.11 Lysogeny or Lytic? The Lysogenic Cycle Figure 13.12 Animal virus infection • • • • Attachment Penetration (endocytosis) Uncoating Biosynthesis Attachment, Penetration, and Uncoating Figure 13.14 Release of an enveloped virus by budding Figure 13.20 Multiplication of DNA Virus Papovavirus 1 Virion attaches to host cell 7 Virions are released Host cell DNA Capsid DNA 2 Virion penetrates cell and its DNA is uncoated Cytoplasm 6 Virions mature Capsid proteins mRNA 5 Late translation; capsid proteins are synthesized 4 Late transcription; DNA is replicated 3 Early transcription and translation; enzymes are synthesized Figure 13.15 Viruses and Cancer. • Viruses incorporated in to the host genome can cause mistakes and errors resulting in unchecked growth of the cell. • It this accidental or are these sites targeted? • Latent Viral Infections – Virus remains in asymptomatic host cell for long periods • Cold sores, shingles • Persistent Viral Infections – Disease processes occurs over a long period, generally fatal • Subacute sclerosing panencephalitis (measles virus) Prions • Infectious proteins • Inherited and transmissible by ingestion, transplant, & surgical instruments • Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease • PrPC, normal cellular prion protein, on cell surface • PrPSc, scrapie protein, accumulate in brain cells forming plaques Prions PrPSc PrPc 1 2 3 4 Lysosome Endosome 5 6 7 8 Figure 13.21 Topics on the flue • http://content.nejm.org/cgi/content/full/NEJ Me0903995 • NEJM N1H1 site http://h1n1.nejm.org/ • An Old presentation http://www.strongnet.org/17152052911421 0850/lib/171520529114210850/Influenza_ presentation.pdf