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13-a Viruses

13-a Viruses. pp. 387-415. H1N1. Viruses. Size, Structure, Morphology Taxonomy Growth Identification. Characteristics of Viruses. Obligate intracellular parasite. SMALL size One type of nucleic acid, either DNA or RNA Protein coat, surrounds the NA Few or no enzymes of their own.

raphael-powell
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13-a Viruses

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  1. 13-a Viruses pp. 387-415 H1N1

  2. Viruses Size, Structure, Morphology Taxonomy Growth Identification

  3. Characteristics of Viruses Obligate intracellular parasite SMALL size One type of nucleic acid, either DNA or RNA Protein coat, surrounds the NA Few or no enzymes of their own

  4. Inert Outside Living Host Cells Multiply inside living host cells by using synthesizing machinery of the cell Proteins, generate ATP Specialized structures to transfer viral NA to other cells Significant for development of antiviral drugs Because most drugs would also interfere with functioning of host cell = toxic

  5. Criteria used to ‘Classify’ Viruses A virion contains: 1. Protein coat (capsids) Capsomeres (make up capsids) The number varies The types of protein very 2. Nucleic acids 3. Size 4. Morphology Can’t use biochemical tests or disease symptoms as for classification

  6. Sizes Figure 13.1

  7. Viral Structure • Nucleic acids • DNA or RNA is • Either single or double stranded • Linear or circular • In segments • Example: influenza virus

  8. Capsid Protein coat protects nucleic acid Capsomere Each capsid composed of protein subunits Arrangement of capsomeres is characteristic of a particular type of virus Envelope(on some viruses) Covers the capsid Spikes CHO-protein, project from envelope surface for attachment

  9. Viral Morphology • Helical • Polyhedral • Enveloped • Complex ‘Group’ into several different morphological types …based on their capsid architecture

  10. Helical • Long rods • Rigid / flexible • NA in center • Diseases: • Ebola hemorrhagic fever • Rabies Fig. 13.4a, b

  11. Polyhedral • Non-enveloped • ‘many sided,’ 20 ‘faces’ • Icosahedron • Diseases: • Adenovirus • Poliovirus Fig. 13.2

  12. Enveloped • Covered • Roughly spherical • Enveloped helical • Enveloped polyhedral • Spikes • Diseases: • Influenza (EH) • Herpes simples (EP) • Flu, fever blisters, chickenpox, shingles, mononucleosis Fig. 13.3

  13. Complex – 1 • Bacteriophage • Capsids with additional structures • Head contains NA • Tail sheath, fibers, plate, pin • Diseases: • Infect bacteria Fig. 13.5

  14. Complex – 2 • Poxvirus • No clearly identifiable capsids • Have several coats • NA inside the coats • Disease: • Smallpox Fig. 13.5

  15. Viral Taxonomy Viral species: A group of viruses sharing the same genetic information and ecological niche (host)

  16. Taxonomy Examples

  17. Viral Growth • Can’t use bacteriological media • Bacteriophages infect bacteria and grow cultures on plates • Grow only in higher primates & humans • Use animal cell culture techniques • Provide living cells • Viruses that infect bacteria useful for understanding growth • Pathogenic viruses difficult to cultivate

  18. Bacteriophage • Bacteriophages form plaques on a lawn of bacteria • It’s a virus that infects bacteria • Plaque is a ‘clearing’ in the bacterial ‘lawn’ • Count, PFU’s • PFU: plaque forming units Fig. 13.6

  19. Viral Growth in Living Cells • Animal viruses grown in living animals or in embryonated eggs • Vaccine production Figure 13.7

  20. Viral Growth in Cell Culture Animal and plant viruses grown in cell culture • Continuous animal cell lines maintained indefinitely • Famous cell line: HeLa Figure 13.8

  21. Viral Identification – Not Easy • Too small to see • Western blotting • Virus kills host cell • Restriction fragment length polymorphism • Polymerase chain reaction • Observe with electron microscope • Serological methods • Cytopathic effects • RFLP’s • PCR

  22. Viral Identification – Cytopathic Effect Uninfected (mo) cells Infected (mo) cells, 24 hrs later Cytopathic effect (CPE): a visible effect on a host cell, may result in host cell death; ‘host’ cells deteriorate Figure 13.9

  23. Q: • Which of the following statements is NOT true? • Viruses contain DNA or RNA • The nucleic acid of a virus is surrounded by a protein coat • Viruses multiply inside living cells using viral mRNA, tRNA and ribosomes • Viruses cause the synthesis of specialized infectious elements • Viruses multiply inside living cells

  24. Q: • In which of the following ways do viruses differ from bacteria? • Viruses are filterable • Viruses are obligate intracellular parasites • Viruses don’t have any nucleic acid • Viruses are not composed of cells • All of the above • Virus spikes are used for attachment to the host cell. True False

  25. Q: • What type of cell is the virus, seen in the figure, capable of infecting? • A liver cell • A plant cell • A bacterial cell • Many different cell types • Viruses range in size from 20-1000 nm in length and are easy to see in a compound light microscope. True False

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