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Eukaryotes and Viruses

Eukaryotes and Viruses. Chapters 12 and 13. Viral Characteristics and Structure. Why Viruses aren’t Alive. General Characteristics of Viruses. Name derives from the Latin for “poison” Obligatory intracellular parasites Referred to as filterable Contain a single type of nucleic material

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Eukaryotes and Viruses

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  1. Eukaryotes and Viruses Chapters 12 and 13

  2. Viral Characteristics and Structure Why Viruses aren’t Alive

  3. General Characteristics of Viruses • Name derives from the Latin for “poison” • Obligatory intracellular parasites • Referred to as filterable • Contain a single type of nucleic material • The nucleic material is covered in a protein coat. • Use the synthesis machinery of the host to multiply.

  4. Why are they not Alive? • No independent metabolism or reproduction • No single phylogenetic origin • No cellular structure • No ribosomes • Though they DO evolve and reproduce.

  5. Host Range • Viruses have a specific subset of cell types they will infect, referred to as Host Range. • Most viruses can only infect a single species • Some viruses can cross species barriers • Numerous factors influence host range • Viruses that infect bacteria are referred to as bacteriophage or simply phage.

  6. Viral Particle Size Staphylococcus Bacteria 1 μm in diameter Poxviridae Lentiviruses Picornaviridae Bacteriophage

  7. Viral Structure • A Virionis a complete, infectious viral particle and is composed of… • Nucleic Acid • Capsid and Envelope

  8. Nucleic Acid • Only a single type of nucleic acid (RNA or DNA) is present in any species of virus. • Unlike cellular life, viral nucleic acid can be either single or double-stranded (again only a single type per species) • Size of the genetic structure can range from a few thousand base pairs to a quarter of a million

  9. Capsid and Envelope • Capsids are regular repeating protein structures composed of capsomeres. • Some viral species also have a host-derived envelope surrounding the capsid • Some viral species have protein/ carbohydrate “spikes” rising from the surface that can be used for identification

  10. Viral Morphology

  11. Viral Taxonomy How do you do a taxonomy of something that isn’t alive?

  12. Viral Taxonomy • Without a shared phylogeny there is no use for the higher taxons (Domain, Kingdom, Phylum, and Class) • Typically viral species are referred to by Order, Family, Genus and a descriptive common name (in place of a species epithet) • Based on • Nucleic Acid type • Strategy of replication • Morphology • Host range

  13. Viral Replication No, not 1 becomes 2, more like 1 becomes 1000.

  14. Growing Bacteriophage

  15. Growing Animal Viruses

  16. Viral Identification • Polyphasic Identification • Morphology • Detection of Antibodies • Western Blotting of known viral proteins • Nucleic Methodologies • PCR • RFLP • RNA PCR

  17. Lytic Bacteriophage Cycle Attachment Release Penetration Maturation Biosynthesis

  18. Lysogenic Bacteriophage Cycle Lytic Cycle

  19. Animal Unenveloped DNA Viral Replication

  20. DNA vs. RNA Viral Replication • There are various types of RNA viruses. • Replication of the Genetic Material can be simple or a multistep process. • +RNA, direct translation and replication by viral protein • -RNA, indirect translation and replication by viral protein • dsRNA, direct translation and relication by viral protein • Retroviruses, conversion of RNA to DNA, integration and then production by host.

  21. Comparison Bacteriophage Animal Attachment to plasma membrane proteins and glycoproteins. Capsid enters cells Capsid removed by enzymes Biosynthesis in nucleus or cytoplasm Latency Enveloped viruses bud and nonenveloped rupture. • Attachment to Cell Wall proteins. • Viral DNA is injected into cell • No removal of capsid required • Biosynthesis in cytoplasm • Lysogeny • Host cell lysed for release

  22. Viruses and Cancer One of many factors

  23. Oncogenic Viruses • Some viruses and known to help trigger cancers, called oncogenic viruses. • These viruses affect oncogenes, natural parts of our genetic structure that can cause cancer. • The process of becoming cancerous is termed transformation. • Oncogenic Viruses integrate into the host genetic material.

  24. Known Oncogenic Viruses

  25. Latency, Persistence and the Prions

  26. Acute, Latent, and Persistent Viral Infections • Acute Infections are those that cause immediate proliferation. • Latent infections can occur by itself or after an acute infection, where the viral load remains undetected for a long period of time before reemerging quickly. • Persistent Infections are ones where the viral load build over a long period of time.

  27. Graph of Acute, Latent and Persistent Viral Infections

  28. Prions • Prions are infectious protein particles • Prions are altered forms of a normal protein in the host that can catalyze the alteration of other “normal” protein particles to the “prion” state • They cause neurological degradation and death with no known treatment. • Since each prion protein is infectious, they are extremely resistant to control measures.

  29. Prion Reaction PrPC + PrPSc 2 PrPSc

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