nester14 - Important Point: Chapter 14: Virions, Prions,...

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Unformatted text preview: Important Point: Chapter 14: Virions, Prions, and Viroids Infectious Agents of Animals and Plants Vertebrate RNA Viruses More RNA Viruses Vertebrate DNA Viruses Routes of Transmission 1 Entry of Enveloped Viruses Steps not seen with Phage 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 Some viruses are acquired via a respiratory route but cause symptoms elsewhere so aren’t considered “respiratory” viruses; example: measles virus Entry of Enveloped Viruses Routes of Transmission 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 Note that viral proteins remain on outside of cell and therefore exposed to host immunity. Many Transcription Strategies Fusion occurs with vesicle membrane rather than plasma membrane Note that viral proteins don’t remain on outside of cell. Don’t worry about virus names (in red). 2 In other words, the greater the size of a virus’ genome, the less dependent that virus is on the host metabolism. Uninfected cells. Cells infected with adenovirus. Not all enveloped viruses bud through the plasma membrane. Note though that naked animal viruses generally lyse their host cell to effect virion release. Various Impacts of Animal Viruses on Cells Impact is virustype and also host-cell type specific. Concentrate on the non-tumorgenic aspects of viral infection. HIV Life Cycle (through virion maturation) Cells infected with HSV. (through reverse transcription) HIV Life Cycle Cytopathic Effects Cytopathic Effects are changes virus infection makes on host-cell morphologies. Budding of Enveloped Viruses Dependence on Host Enzymes Note that maturation actually takes place via virion budding!!! 3 E.g., swapping of coat proteins between avian and human strains of influenza virus. Time Course of Infections (budding through plasma membrane) HIV Life Cycle How the Flu Changes its “Spots” Hypothesis for Prion Action Reverse transcriptase enzyme already incorporated into capsid. Prion-Associated Disease 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) These are all Transmissible Spongiform Encephalopathies and all appear to be caused by proteinaceous infectious agents called Prions. Link to Next Presentation Accumulated abnormal proteins kill neuron, with prions spreading to adjacent neurons. 4 Entry of Enveloped Viruses Note that viral proteins remain on outside of cell and therefore exposed to host immunity. 14 Entry of Enveloped Viruses Fusion occurs with vesicle membrane rather than plasma membrane Note that viral proteins don’t remain on outside of cell. 14 Many Transcription Strategies Don’t worry about virus names (in red). 14 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. 14 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. 14 Various Impacts of Animal Viruses on Cells Impact is virustype and also host-cell type specific. Concentrate on the non-tumorgenic aspects of viral infection. 14 HIV Life Cycle (through reverse transcription) 14 (through virion maturation) HIV Life Cycle Note that maturation actually takes place via virion budding!!! 14 (budding through plasma membrane) HIV Life Cycle Reverse transcriptase enzyme already incorporated into capsid. 14 How the Flu Changes its “Spots” E.g., swapping of coat proteins between avian and human strains of influenza virus. 14 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) Hypothesis for Prion Action Accumulated abnormal proteins kill neuron, with prions spreading to adjacent neurons. 14 ...
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