ch 12

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ch 12
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2011-02-23 20:16:55
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ch 12
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  1. What/who are the victims of viral infections?
    Bacteria, Plants, Animals, Humans and even the best scientist and doctors. The only thing protected from viruses are other viruses.
  2. Viron
    • Viron: a single viral particle that is intact.
    • Has 2 challanges it must meet
    • Viron must be strong enough to withstand the enciroment in chich it must survive until it successfully infescts a host cell (this depends on strength of capsid)
    • The viron must be able to shed its protective protein coat easily on entry into a host cell.
  3. Capsid
    • The protein coat that surrounds the Virus DNA (genetic material)
    • 2 types; DNA and RNA. Depends what type of nucleic acid they can.
  4. Nucleocapsid
    nucleic acid plus capsid
  5. Envelope
    Phospholipid bilayer with emmbeded glycoproteins surrounding capsid in enveloped virus
  6. Compare and contrast lytic and lysogenic infections
    Lytic: host cell fills w/ virons and bursts which leads to cell death; hallmark sin of lytic infectionLysogenic infections: are known as latent infections. The viral genome becomes incoporated into the host cells DNA. The host cell will still live. The virus can stay latent for extended amounts of time. With a latent infection there is no new virus made and no increase infection.
  7. What are the six stages of lytic infection?
    • 1.) attachment
    • 2.) penetration
    • 3.) uncoating
    • 4.) biosynthesis
    • 5.) maturation
    • 6.) release
  8. Attachment
    • Occurs when a virion binds to specific receptors on a host cell
    • Virus randomly collides with host cell, governed by chance
    • The concentration of viral particles will determine likelihood of infection
    • Sometimes, the virus just binding to the receptor isn’t enough to cause infection, and the host cell has to be permissive (have the capacity to produce new virions)
    • Many different plasma membrane molecules on the host cell can serve as receptors for virus attachment.
  9. Uncoating within endosome
    virus pulled in through endosome. Endosome has a specific ph and chemical which will help uncoat it.
  10. uncoating at nuclear membrane
    (1 of the most dangerous forms) DNA goes directly into the nucleus; there is no way the nucleic acid can get blocked it starts replicating the DNA
  11. Biosynthesis
    • replicate nucleic acid or DNA create a capsomere protein.
    • single stranded simply add another strand so its double stranded, it doesn’t recognize its foreign.
    • Replication of viral genomes requires several proteins that are also seen in replication of host cell
    • Viral DNA replication occurs at specialized sites in the host cell, which contributes to the efficiency and productivity of the viral infection (dose numbers are important)
    • Transcription of the viral DNA is performed by the host cell’s RNA polymerase
    • Viral genomes are replicated at a high rate to make as many new virons as possible
    • Latent DNA viruses, special mRNA sequence inhibit the lytic cycle and allow the viral DNA to integrate w/ the host chromosome.
  12. Penetration
    Virion gains access to interior of cell. Since virion is enclose in a capsid or capsid and envelop, it must “uncoat”
  13. Penetration and uncoating by non-enveloped viruses
    • Use receptor mediated endocytosis to gain entry into host cell.
    • Virion binds to a receptor on the host cell’s plasma membrane, causing a pit to form in the membrane.
    • The membrane encloses around it and forms a vesicle called an endosome.
    • The endosome travels through the cytoplasm and becomes acidic.
    • This acidity is what starts to uncoat the virion
    • Use lysis to gain entry which causes death to host cell
  14. Penetration and uncoating by enveloped viruses
    • The envelope is a plasma membrane and simply fuses with host cell’s plasma membrane
    • This fusion results in a large opening called a “fusion pore” in the host cell.
    • Fusion is catalyzed by a specialized viral glycoprotein called a fusion protein, whose function is highly regulated
    • The virion moves through this and into the host cell where uncoating is made possible by several mechanisms
    • Uses “budding” or “pinching” to gain entry which allows cell to live for a while
  15. How are virions spread from cell to cell in an animal host?
    • Use specialized cellular junctions called tight junctions to go from epithelial tissue to epithelial tissue and neuron to neuron.
    • They can also spread through the formation of syncytia: multinucleate masses formed by the fusion of many infected cells into one gigantic cell.
    • Decoy virons: which are either empty capsids or non-infectious virons, and release a large number of them from infected cells. the decoys confuse and distract the host defenses so the real virus particles ca achieve infection of new host cells.
  16. What type of symmetry to viruses have?
    • Viruses have either icosahedral or helical symmetry
    • Icosahedral: derived from 20 triangular faces which gives the capsid 12 points
    • Helical: have either a rod shape or a filamentous shape
  17. Is RNA or DNA virus replication more complicated?
    RNA virus replication is more complicated than DNA virus replication
  18. What are retroviruses?
    Retroviruses are RNA viruses that contain the enzyme reverse transcriptase (causes latent infections)

    • reverse transcriptase converts RNA into DNA
    • Converted viral DNA can be inserted into the host cell chromosome
  19. What are viruses?
    Viruses are obligate intracellular parasites because they cannot “live” outside a host cell
  20. What are bacteriophages?
    Bacteriophages (phages)- viruses that infect bacteria

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