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Chapter 13

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Chapter 13

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  1. Chapter 13 Viruses, Viroids, and Prions

  2. Viruses • Viruses contain DNA or RNA • And a protein coat • Some are enclosed by an envelope • Some viruses have spikes • Most viruses infect only specific types of cells in one host • Host range is determined by specific host attachment sites and cellular factors

  3. Viruses Figure 13.1

  4. Helical Viruses Figure 13.4a, b

  5. Polyhedral Viruses Figure 13.2a, b

  6. Complex Viruses Figure 13.5a

  7. Viral Taxonomy • Family names end in -viridae • Genus names end in -virus • Viral species: A group of viruses sharing the same genetic information and ecological niche (host). Common names are used for species • Subspecies are designated by a number

  8. Viral Taxonomy • Herpesviridae • Herpesvirus • Human herpes virus 1, HHV 2, HHV 3 • Retroviridae • Lentivirus • Human Immunodeficiency Virus 1, HIV 2

  9. Growing Viruses • Viruses must be grown in living cells. • Bacteriophages form plaques on a lawn of bacteria. Figure 13.6

  10. Growing Viruses • Animal viruses may be grown in living animals or in embryonated eggs. Figure 13.7

  11. Growing Viruses • Animal and plants viruses may be grown in cell culture. • Continuous cell lines may be maintained indefinitely. Figure 13.8

  12. Virus Identification • Cytopathic effects • Serological tests • Detect antibodies against viruses in a patient • Use antibodies to identify viruses in neutralization tests, viral hemagglutination, and Western blot • Nucleic acids • RFLPs • PCR

  13. Virus Identification Figure 13.9

  14. Multiplication of Bacteriophages (Lytic Cycle) • Attachment Phage attaches by tail fibers to host cell • Penetration Phage lysozyme opens cell wall, tail sheath contracts to force tail core and DNA into cell • Biosynthesis Production of phage DNA and proteins • Maturation Assembly of phage particles • Release Phage lysozyme breaks cell wall

  15. Bacterial cell wall Bacterial chromosome Capsid DNA Capsid Sheath Tail fiber Tail 1 Attachment:Phage attaches to host cell. Base plate Pin Cell wall Plasma membrane 2 Penetration:Phage pnetrates host cell and injects its DNA. Sheath contracted Tail core 3 Merozoites released into bloodsteam from liver may infect new red blood cells Figure 13.10.1

  16. Tail DNA 4 Maturation:Viral components are assembled into virions. Capsid 5 Release:Host cell lyses and new virions are released. Tail fibers Figure 13.10.2

  17. One-step Growth Curve Figure 13.11

  18. Lytic cycle Phage causes lysis and death of host cell • Lysogenic cycle Prophage DNA incorporated in host DNA

  19. The Lysogenic Cycle Figure 13.12

  20. Specialized Transduction gal gene Bacterial DNA Prophage 1 Prophage exists in galactose-using host (containing the gal gene). Galactose-positive donor cell gal gene 2 Phage genome excises, carrying with it the adjacent gal gene from the host. 3 Phage matures and cell lyses, releasing phage carrying gal gene. gal gene 4 Phage infects a cell that cannot utilize galactose (lacking gal gene). Galactose-negative recipient cell 5 Along with the prophage, the bacterial gal gene becomes integrated into the new host’s DNA. 6 Lysogenic cell can now metabolize galactose. Galactose-positive recombinant cell Figure 13.13

  21. Multiplication of Animal viruses • Attachment Viruses attaches to cell membrane • Penetration By endocytosis or fusion • Uncoating By viral or host enzymes • Biosynthesis Production of nucleic acid and proteins • Maturation Nucleic acid and capsid proteins assemble • Release By budding (enveloped viruses) or rupture

  22. Attachment, Penetration, and Uncoating Figure 13.14

  23. Release of an enveloped virus by budding Figure 13.20

  24. Multiplication of DNA Virus Papovavirus 1 Virion attaches to host cell 7 Virions are released Host cell DNA Capsid 2 DNA Virion penetrates cell and its DNA is uncoated Cytoplasm 6 Virions mature Capsid proteins mRNA 5 Late translation; capsid proteins are synthesized 3 Early transcription and translation; enzymes are synthesized 4 Late transcription; DNA is replicated Figure 13.15

  25. Pathways of Multiplication for RNA-Containing Viruses Figure 13.17

  26. Multiplication of a Retrovirus Capsid Reverse transcriptase DNA Virus Two identical + stands of RNA 1 Retrovirus penetrates host cell. Host cell DNA of one of the host cell’s chromosomes 5 Mature retrovirus leaves host cell, acquiring an envelope as it buds out. Reverse transcriptase 2 Virion penetrates cell and its DNA is uncoated Viral RNA Identical strands of RNA 4 Transcription of the provirus may also occur, producing RNA for new retrovirus genomes and RNA that codes for the retrovirus capsid and envelope proteins. Viral proteins RNA 3 The new viral DNA is tranported into the host cell’s nucleus and integrated as a provirus. The provirus may divide indefinitely with the host cell DNA. Provirus Figure 13.19

  27. Cancer • Activated oncogenes transform normal cells into cancerous cells. • Transformed cells have increased growth, loss of contact inhibition, tumor specific transplant and T antigens. • The genetic material of oncogenic viruses becomes integrated into the host cell's DNA.

  28. Oncogenic Viruses • Oncogenic DNA Viruses • Adenoviridae • Heresviridae • Poxviridae • Papovaviridae • Hepadnaviridae • Oncogenic RNA viruses • Retroviridae • Viral RNA is transcribed to DNA which can integrate into host DNA • HTLV 1 • HTLV 2

  29. Latent Viral Infections • Virus remains in asymptomatic host cell for long periods • Cold sores, shingles • Persistent Viral Infections • Disease processes occurs over a long period, generally fatal • Subacute sclerosing panencephalitis (measles virus)

  30. Prions • Infectious proteins • Inherited and transmissible by ingestion, transplant, & surgical instruments • Spongiform encephalopathies: Sheep scrapie, Creutzfeldt-Jakob disease, Gerstmann-Sträussler-Scheinker syndrome, fatal familial insomnia, mad cow disease • PrPC, normal cellular prion protein, on cell surface • PrPSc, scrapie protein, accumulate in brain cells forming plaques

  31. Prions PrPSc PrPc 2 3 4 1 Lysosome Endosome 5 6 7 8 Figure 13.21

  32. Plant Viruses • Plant viruses enter through wounds or via insects • Viroids • Viroids are infectious RNA; potato spindle tuber disease Figure 13.22

  33. Some Plant Viruses Table 13.6

  34. Virus Families • Single-stranded DNA, nonenveloped viruses • Parvoviridae • Human parvovirus • Fifth disease • Anemia in immunocompromised patients

  35. Double-stranded DNA, nonenveloped viruses • Mastadenovirus • Respiratory infections in humans • Tumors in animals

  36. Double-stranded DNA, nonenveloped viruses • Papillomavirus (human wart virus) • Polyomavirus • Cause tumors, some cause cancer

  37. Double-stranded DNA, nonenveloped viruses • Orthopoxvirus (vaccinia and smallpox viruses) • Molluscipoxvirus • Smallpox, molluscum contagiosum, cowpox

  38. Double-stranded DNA, nonenveloped viruses • Simplexvirus (HHV1 and HHV 2) • Varicellavirus (HHV 3) • Lymphocryptovirus (HHV 4) • Cytomegalovirus (HHV 5) • Roseolovirus (HHV 6) • HHV 7 • Kaposi's sarcoma (HHV 8) • Some herpesviruses can remain latent in host cells

  39. Double-stranded DNA, nonenveloped viruses • Hepadnavirus (Hepatitis B virus) • Use reverse transcriptase to produce DNA from mRNA

  40. Single-stranded RNA, + strand, nonenveloped • Enterovirus • Enteroviruses include poliovirus and coxsackievirus • Rhinovirus • Hepatitis A virus

  41. Single-stranded RNA, + strand, nonenveloped • Hepatitis E virus • Norovirus (Norwalk agent) causes gastroenteritis

  42. Single-stranded RNA, + strand, nonenveloped • Alphavirus • Alphaviruses are transmitted by arthropods; include EEE, WEE • Rubivirus (rubella virus)

  43. Single-stranded RNA, + strand, nonenveloped • Arbovirusescan replicate in arthropods; include yellow fever, dengue, SLE, and West Nile viruses • Hepatitis C virus

  44. Single-stranded RNA, + strand, nonenveloped • Coronavirus • Upper respiratory infections

  45. Single-stranded RNA, – strand, one RNA strand • Vesiculovirus • Lyssavirus (rabies virus) • Cause numerous animal diseases

  46. Single-stranded RNA, – strand, one RNA strand • Filovirus • Enveloped, helical viruses • Ebola and Marburg viruses

  47. Single-stranded RNA, – strand, one RNA strand • Paramyxovirus • Morbillivirus • Paramyxovirus causes parainfluenza, mumps and Newcastle disease

  48. Single-stranded RNA, – strand, one RNA strand • Hepatitis D virus • Depends on coinfection with Hepadnavirus

  49. Single-stranded RNA, – strand, multiple RNA strands • Influenzavirus (Influenza viruses A and B) • Influenza C virus • Envelope spikes can agglutinate RBCs

  50. Single-stranded RNA, – strand, multiple RNA strands • Bunyavirus (CE virus) • Hantavirus