Presentation on theme: "Eukaryotic Viruses Taxonomy characters: nucleic acid type; enveloped or naked; capsid shape; assembly site in host (nucleus or cytoplasm)"— Presentation transcript:
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).
Enveloped virus fusing with endosome membrane for release of capsid. NOTE: in both mechanisms the nucleic acid is “uncoated”, i.e. capsid disassembles.
DNA virus Papovavirus (warts) Transcription & replication in nucleus; capsid assembly in nucleus. Release by exocytosis
RNA Virus Types Polio; common cold (RdRp) In the cytoplasm. In the cytoplasm; except influenza
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):
RNA viruses = respiratory enteric orphan viruses In the cytoplasm.
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.