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).
NOTE: in both mechanisms
the nucleic acid is “uncoated”,
i.e. capsid disassembles.
Enveloped virus fusing with
endosome membrane for
release of capsid.
Release
by
exocytosis
DNA virus
Papovavirus
(warts)
Transcription & replication in nucleus; capsid assembly in nucleus.
RNA Virus Types
Polio; common cold
In the cytoplasm.
(RdRp)
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.
In the cytoplasm.
Retrovirus
(+RNA)
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:
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–
–
–
–
–
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)
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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.