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Eukaryotic Viruses

Eukaryotic Viruses. Taxonomy characters: nucleic acid type; enveloped or naked; capsid shape; assembly site in host (nucleus or cytoplasm). Attachment and Penetration: Attachment phase is conceptually similar to phage. Penetration can be very different (capsid may enter).

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Eukaryotic Viruses

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  1. Eukaryotic Viruses • Taxonomy characters: • nucleic acid type; • enveloped or naked; • capsid shape; • assembly site in host (nucleus or cytoplasm)

  2. Attachment and Penetration: Attachment phase is conceptually similar to phage. Penetration can be very different (capsid may enter).

  3. NOTE: in both mechanisms the nucleic acid is “uncoated”, i.e. capsid disassembles. Enveloped virus fusing with endosome membrane for release of capsid.

  4. DNA virus Papovavirus (warts) Release by exocytosis Transcription & replication in nucleus; capsid assembly in nucleus.

  5. RNA Virus Types Polio; common cold In the cytoplasm. (RdRp) In the cytoplasm; except influenza

  6. Orthomyxoviruses (Influenza Virus): • Attachment and penetration by endocytosis, then -ssRNA is uncoated. • Unique for RNA viruses to replicate in the nucleus; Uses RdRp to make +ssRNA then to –ssRNA. • Needs a capped primer (C) for mRNA synthesis and ribosome recognition; steals C from host mRNA at 5’end. • Viral envelope proteins transported from RER to GA to plasma membrane; others associate with –ssRNA to form nucleocapsid. Budding release (below):

  7. RNA viruses = respiratory enteric orphan viruses In the cytoplasm. In the cytoplasm.

  8. Retrovirus (+RNA)

  9. Infection Types and Outcomes • Acute versus Persistent Infections: • Chronic (replicates at low levels & constant yet mild symptoms) • Latent (stops reproduction after initial infection; goes dormant until induced to activate replication again) • Slow (vary slow replication and spread; years before symptoms) • Cytocidal effects (death) and cell damage: • Inhibit host macromolecule synthesis • Lysosome malfunction (host cell self digests) • Plasma membrane abnormalities • Direct viral protein toxicity • Protein aggregation (inclusion bodies) • Host cell changes to a malignant cell (cancer) • Tumors form by neoplasia and anaplasa; may spread by metastasis. • Virus may carry oncogenes (genes for various cancer causing protein). • Viral promotors may insert and turn on expression of host oncogenes. • 8 cancers involving viruses: Burkitt’s lymphoma and nasopharyngeal carcinoma (Epstein-Barr virus); cervical cancer (papillomavirus); Kaposi’s sarcoma (herpes 8), Hepatitis B & C, T-cell and hairy-cell leukemias, Rous sarcoma.

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