Virions
Terms
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- Nucleocapsid
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Nucleic acid within a symmetrical protein coat.
Enveloped viruses have a lipo-protein membrane around the nucleocapsid - Protein coats
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Identical building blocks (capsomers) arranged in helical or icosahedral (20-sided) symmetry
Antigens involved in neutralization - Multiplication of the animal unenveloped nucleocapsids
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1. adsorption of virion to specific receptor on host cell membrane
2. Entry of viral nucleic acid into host cell cytoplasm (eclipse period begins)
3. Synthesis of viral proteins and nucleic acid
4. Assembly of new virions (eclipse period ends)
5. Lysis of host cell and release of virions - What kinds of immune system is involved in the antiviral response?
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1) Humoral (ab) response --> neutralization can be carried out by all classes of ab; viral ag = proteins on the surface of the virion;
ab+nucleocapsid make a tight complex; no effect on intracellular multiplication of viruses
2) cell-mediated immune response - Which type of immunoglobulin is the most important defense against viruses in respiratory (e.g. influenza)and GI (e.g. polio) tracts?
- IgA
- What is HOST RANGE?
- Species of animal that can be infected by a given virus; determined by adsorption of virions to the receptor protein in the host cell membrane; highly specific
- What is TISSUE TROPISM?
- Specific tissues that can be infected
- What happens when you add phenol and water to a polio viron culture?
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water phase = RNA
Phenol pahse = Protein
Protein-free RNA can infect any cell - By what mechanism does polio virus replicate inside the host cell?
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By RNA-dependent RNA polymerase
1) No DNA involved: Actinomycin D inhibit the synthesisof RNA on a DNA template --> No cell growth or DNA viruses
2) Viral RNA made in the cytoplasm
3)Host DNA, RNA and protein syntheses are inhibited. - Sequence of events early in infection of piconarvirus
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1. Viral RNA acts as mRNA with host ribosomes --> a very large protein
2. The protein cleaved to 8 functional proteins (e.g. capsomer, RNA-dependent RNA polymerase, etc.)
3. RNA-dependet RNA polymerase uses the viral RNA as a template --> make complementary (minus-stranded) RNA
4. Syntehsis of more plus strands from minus strand
5. Assembly of plus-stranded RNA and capsomers. - Would minus-stranded RNA found in polio virion?
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No,they would be only found in infected cells after the synthesis of viral RNA polymerase.
The molecular species involved in virion RNA synthesis is the replicative intermediate. A minus strand in replication will have several viral + strand RNA growing and polymerases attached to it. - Viremia
- Infectious virions in the blood
- Inculation period
- The length of time (days to years) between infection and the onset of specific symptoms
- Three general patterns of pathogenesis (omitting specific symptoms)
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1)Virus grows at site with no disease followed by viremia.
2) Virus grows at site causing disease locally
3) Virus grows at site but spreads via neurons