NU BIOL 1121 - Bovine Spongiform encephalopathy

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Bovine Spongiform encephalopathy- Mad Cow disease- Closely related to scrapie in sheep- Kuru in the native tribes - Then discovered to be a protieneous infectious particle (prion) o Because no immune symptoms o Symptoms occur long after initial infectiono PcP is similar to the human chromosome of PrPcStructure and Classification of Animal Viruses- Viral structureo Capsid: the protein coat of a viruso Nucleocapsid: the nucleic acid and the protein capsid together o Capsomers: defined units that when bonded covalently form the capsido Naked: if there are no additional covering, the virus is deemed a naked viruso Envelope: a lipid covering that surrounds the outsite of the capsid in most animal viruses Rarely found in phage bacteria Similar to the structure of the human cell membraneo Matrix protein: found right inside the lipid envelopeo Attachment proteins, or spikes: extend from the capsid or envelope- Segmented viruses: viruses vary in the number of genes and RNA moleculeso Ex: influenza has 8 RNA, each coding for 8 genes- Viral shapeso Isometric: in which protein subunits are arranged in groups of equilateral triangles Icosahedral symmetry: 20 triangular faces enclose the nucleic acid o Pleomorphic: irregular shape Phage is most common type- Classification of Animal Viruseso Genome structure RNA or DNA Double stranded vs single stranded Single molecule or segmentedo Virus particle structure Isometric, helical (rod-shaped), or pleomorphico Presence or absence of a viral envelope - Grouping based on routes of transmissiono Enteric virus Usually a fecal-oral transmission  Replicate in the intestinal tract and often cause gastroenteritis (stomach and GI inflammation) Polio replicates in the stomach making a systemic disease and not just gastroenteritiso Respiratory virus Inhaled droplets and replicate in the respiratory tract  Viruses that go on to cause systemic disease are not considered respiratory (mumps, etc)o Zoonoses of Zoonotic virus Animal to human and vice versa Vector, like arthopodso Sexually transmitted disease Lesions in the genital tractInteraction of Animal Viruses and with their hosts- Viral infection is a result of many factorso Antibody presenceo Balanced pathogenicity: in which neither the virus or the host is in serious danger - Acute infectiono Usually self-limited diseases in which the host often remains localized and disappears when the disease endso Short duration illnesses in which the host develops long-term immunityo Cause productive infectionso Coated viruses rarely cause cell lysiso Reproductive Cycle of a virus Attachment- In animal viruses, the surface of the virus is covered in spikes- Several attachment proteins exists and they attach to the glycoprotiens located on the plasma membraneo The glycoprotiens on the cell that help the virus attach are unrelated to viral attachment, normally have another major role for the cell- When bind changes the viral shape, and thus why a virus needs a specific receptor Entry- Enveloped viruseso Fusion of the virus to the plasma membrane after binding with the host receptoro Their coats remain part of the cell membraneo Involves a fusion protein on viron surface- Endocytosiso Virons are taken into the cell via vesicle o Dissolve the vesicle and exit Targeting the site of viral replication- After penetration must find its place of replication- The mechanism is unknown- RNA polymerase enters the cell in the protein capsid because the infected cell does not have that enzymeo Replication of RNA occurs in the cytoplasm- Acids are replicated and proteins are synthesized independently- The large the genome, the smaller number of host enzymes are utilized Maturation- This is the final assembly of the virus with its protein coat - In the TMV, the coat is assembled capsomer by capsomer- Lipid rafts: specific places in the host cell membrane that have embedded specific proteins and is an ideal place for viral maturation Release from cells - Most virons do not code for enzymes to lyse the cell wall, instead because the viral DNA and proteins are synthesized the host cell cannot make its own and therefore dieso Cytopathic effects: change in appearance of the cell normally due to cell degradation and lysis caused by viral enzymes - Budding: release from budding from the cell membrane o Persistant infections and may kill infected cells o First, the region of budding in the membrane acquire spikes that will attach to theviron o Then the inside of the membrane is coated with matrix proteinso Then the virus is enclosed by the lipid raft region: enclosed in the hosts cell membraneo Some viruses bud from other cell organelles and then use the vesicle to reach the cell membrane where they are ejected by exocytosis- Shedding from host o Usually occur the same place the virus entered o i.e. respiratory tract, etc- Transmission to Other Hostso Via routes of transmission- Persistent infectiono Viruses constantly in the body and are being released by budding o Remain for many years without symptomso Latent Persistent infections in which a symptomless period is followed by a time of reactivation withan accompanying period of reactivation with symptoms Infectious particles cannot be detected until resurgence Herpes virus (HV-I and HV-2)- Become latent under varying conditions Chicken pox- Can reactivate and form shingleso Slow  The population of infectious particles gradually increases over a long period of time in which no symptoms arise Lentivirus and Retroviridae (retrovirus) Prions are considered part of this group HIV - Attacks the T lymphocytes and macrophages- Single stranded, enveloped retrovirus- Retrovirus DNARNADNA which is integrated into the host cell- The single stranded molecule is converted into a double stranded DNA and then integrated into the host cell with the aid of reverse transciptase as a provirus- This provirus codes for polygenic or polycistronic mRNA long strands of mRNA which is translated into a polyprotien, which is then cleaved by protease to yield individual proteinso Why protease inhibitors are important o Reverse transciptase has no proof reading mechanism leading to the formation of viral coats that the immune system (antibodies) cannot recognizeo Chronic  Viral particles are seen or absent at all times Heptitisis B Carrier state- The state in which infectious hep B particles are continually produced and


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