Chapter 13 and 14--- Virus - PowerPoint PPT Presentation

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Chapter 13 and 14--- Virus

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  1. Chapter 13 and 14--- Virus

  2. Preview • Characteristics of virus • Basic structure of virus • Life cycle of virus (virulent and temperate) • Replication of viral genome • Culture virus

  3. Release of many viral particles Viral particle (virion) Host cell Viruses - General Information Two general groups: • Those that infect eukaryotic cells • Those that infect prokaryotic cells • Referred to as bacteriophage, or phage • Used as a model to understand animal viruses • Mechanism of DNA transfer • Used to destroy bacteria Nucleic acid inside a protein coat

  4. FDA Consumer magazine January-February 2007 Bacteria-Eating Virus Approved as Food Additive By Linda Bren Not all viruses harm people. The Food and Drug Administration has approved a mixture of viruses as a food additive to protect people. The additive can be used in processing plants for spraying onto ready-to-eat meat and poultry products to protect consumers from the potentially life-threatening bacterium Listeria monocytogenes (L. monocytogenes). The viruses used in the additive are known as bacteriophages. Bacteriophage means "bacteria eater." A bacteriophage, also called a phage (pronounced fayj), is any virus that infects bacteria.

  5. Viruses - General Information Too small to see using a light microscope Figure 13.1

  6. Viral Architecture Genome surrounded by a protein coat (capsid) nucleocapsid naked virus generally more resistant generally eukaryotic viruses only

  7. Viral Architecture Genome surrounded by a protein coat (capsid) phage

  8. Release of many viral particles Viral particle (virion) Host cell Viruses - General Information Viruses multiply only within a host cell • Utilize the host cell’s machinery (viruses lack the ability to harvest energy, synthesize proteins) • Direct that machinery to produce more viral particles Nucleic acid inside a protein coat

  9. Release of many viral particles Viral particle Host cell Viral Interaction with Host Cells burst size • Productive infection • Viral particles released via: • Lysis of host cell (lytic infection) • Extrusion from host • Latent infection

  10. Viral particle Viral Interaction with Host Cells Host cell • Productive infection • Viral particles released via: • Lysis of host cell (lytic infection) • Extrusion from host • Latent infection • Viral genome resides silently within host

  11. Viral particle Viral Interaction with Host Cells Host cell • Productive infection • Viral particles released via: • Lysis of host cell (lytic infection) • Extrusion from host • Latent infection • Viral genome resides silently within host repressor prophage/provirus • Infected bacterial cell is referred to as a lysogen

  12. Viral Genome • Encodes proteins that: • Make up the viral particle (ex. protein coat) • Assure replication of viral nucleic acid • Enable viral particles (virions) to exit host cell, then enter another • Genome consists of RNA or DNA (not both), double-stranded or single-stranded

  13. Bacteriophage Infections

  14. Infection Process (productive) T4 Attachment - via specific receptors on host; lack of receptor  resistance

  15. Infection Process (productive) T4 Penetration - genome is injected into cell

  16. Infection Process (productive) T4 • Transcription/translation • early proteins -ex. nucleases

  17. Infection Process (productive) T4 • Replication of phage • Replication of phage genomeTranscription/translation • early proteins- nuclease, enzymes involves in phage DNA replication. • late proteins - capsid proteins, lysozymes

  18. Infection Process (productive) T4 Assembly - self-assembly

  19. Infection Process (productive) T4 Release - often lysis, sometimes extrusion (lytic phages lyse cells)

  20. Latent infections Lambda • Temperate phage • Two options: • Lytic cycle • Lysogenic cycle Integration/replication Phage “senses” stress-level of host

  21. Latent infections Lambda Immunity of lysogens repressor Lysogenic conversion

  22. Transduction DNA is transferred via a bacteriophage Generalized transduction Specialized transduction - lytic or temperate phage - temperate phage only

  23. Generalized Transduction Initial steps of a typical productive infection Phage-encoded nuclease degrades host DNA

  24. Wild-type phage Transducing particle carries bacterial DNA Generalized Transduction Initial steps of a typical productive infection Phage-encoded nuclease degrades host DNA Error in packaging

  25. Generalized Transduction Initial steps of a typical productive infection Phage-encoded nuclease degrades host DNA Error in packaging

  26. Generalized Transduction Initial steps of a typical productive infection Phage-encoded nuclease degrades host DNA Error in packaging

  27. Specialized Transduction Initial steps generate a lysogen lysogen • begins lytic cycle • incorrect excision

  28. Specialized Transduction Initial steps generate a lysogen • Only DNA that flanks the site of integration can be excised with phage DNA • Some phage genes are left behind lysogen • begins lytic cycle • incorrect excision

  29. defective phage Specialized Transduction Initial steps generate a lysogen • Lytic cyle: • replication of phage parts • assembly • release lysogen • begins lytic cycle • incorrect excision

  30. defective phage Specialized Transduction Initial steps generate a lysogen lysogen • begins lytic cycle • incorrect excision

  31. Viruses that Infect Animal Cells

  32. Infection Process • Attachment • Penetration • fusion with the host membrane (enveloped viruses only)

  33. Infection Process • Attachment • Penetration • fusion with the host membrane (enveloped viruses only) • endocytosis • Replication • genome • protein synthesis • Assembly • Release • Cell death  lysis • Budding

  34. Infection Process • Attachment • Penetration • fusion with the host membrane (enveloped viruses only) • endocytosis • Replication • genome • protein synthesis • Assembly • Release • Cell death  lysis • Budding • acquisition of envelope

  35. Acute Infections

  36. Persistent Infections shingles

  37. ds DNA • ss DNA Replication of the Genome Central dogma

  38. initial template final product DNA polymerase ATCCGTA ATCCGTA Replication of the Genome ds DNA • ss DNA TAGGCAT

  39. initial template final product DNA polymerase Replication of the Genome ds DNA • ss DNA • + strand • - strand

  40. Replication of the Genome ds RNA • ss RNA

  41. Virally-encoded enzyme (replicase) initial template final product 5’ 3’ 3’ 5’ Replication of the Genome Long ds RNA signifies to our cells that they are virally-infected RNA-dependent RNA polymerase ds RNA • ss RNA • (+) strand • (-) strand (mRNA) (-) ss and ds RNA vir. must bring own replicases  made during prev. infec.

  42. Replication of the Genome Retroviruses - ss (+) RNA  ds DNA ss (+) RNA Reverse transcriptase DNA copy integrates into the host cell’s genome

  43. Replication of the Genome Retroviruses - ss (+) RNA  ds DNA ss (+) RNA Reverse transcriptase DNA copy integrates into the host cell’s genome • Virally-encoded enzymes • Target for antiviral drugs • ex. AZT - nucleotide analog • Error-prone ( mutations)

  44. Growing Bacteriophage in the Laboratory Lawn of host cells Plaques

  45. Growing Eukaryotic Viruses in the Laboratory Tissue culture

  46. Growing Eukaryotic Viruses in the Laboratory Tissue culture

  47. Growing Eukaryotic Viruses in the Laboratory Tissue culture