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Chapter 14: Virions, Prions, and Viroids Infectious Agents of Animals and Plants. Important Point:. If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!. Vertebrate RNA Viruses. More RNA Viruses.
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Chapter 14:Virions, Prions, and ViroidsInfectious Agents ofAnimals and Plants
Important Point: If you are having trouble understanding lecture material: Try reading your text before attending lectures. And take the time to read it well!
Routes of Transmission Some viruses are acquired via a respiratory route but cause symptoms elsewhere so aren’t considered “respiratory” viruses; example: measles virus
Attachment to susceptible cell • Uptake of nucleocapsid into cell • Targeting of nucleocapsid to site of reproduction • Uncoating of nucleic acid from capsid • Synthesis of viral proteins • Replication of nucleic acid • Maturation of virion particles • Virion release from cell • Virus spread within host • Exit of virus from host • Transmission of virus to new host Animal Virus Life Cycle
Attachment to susceptible cell • Uptake of nucleocapsid into cell • Targeting of nucleocapsid to site of reproduction • Uncoating of nucleic acid from capsid • Synthesis of viral proteins • Replication of nucleic acid • Maturation of virion particles • Virion release from cell • Virus spread within host • Exit of virus from host • Transmission of virus to new host Steps not seen with Phage
Entry of Enveloped Viruses Note that viral proteins remain on outside of cell and therefore exposed to host immunity.
Entry of Enveloped Viruses Fusion occurs with vesicle membrane rather than plasma membrane Note that viral proteins don’t remain on outside of cell.
Many Transcription Strategies Don’t worry about virus names (in red).
Dependence on Host Enzymes In other words, the greater the size of a virus’ genome, the less dependent that virus is on the host metabolism.
Budding of Enveloped Viruses Not all enveloped viruses bud through the plasma membrane. Note though that naked animal viruses generally lyse their host cell to effect virion release.
Uninfected cells. Cytopathic Effects are changes virus infection makes on host-cell morphologies. Cytopathic Effects Cells infected with adenovirus. Cells infected with HSV.
Various Impacts of Animal Viruses on Cells Impact is virus-type and also host-cell type specific. Concentrate on the non-tumorgenic aspects of viral infection.
HIV Life Cycle(through virion maturation) Note that maturation actually takes place via virion budding!!!
Reverse transcriptase enzyme already incorporated into capsid. HIV Life Cycle(budding through plasma membrane)
E.g., swapping of coat proteins between avian and human strains of influenza virus. How the Flu Changes its “Spots” Particularly important is the protein virus protein, hemagglutinin. But note that “the diversity of influenza sequences worldwide in any given year appears to be roughly comparable to the diversity of HIV sequences found within a single individual at one time point.” (Bette Korder as cited in Microbe, 2006 1(3):111-112)
Prion-Associated Disease These are all Transmissible Spongiform Encephalopathies and all appear to be caused by proteinaceous infectious agents called Prions.
Hypothesis for Prion Action Accumulated abnormal proteins kill neuron, with prions spreading to adjacent neurons.
