Viruses, Viroids, and Prions

1. 13 Viruses, Viroids, and Prions

2. How are they different?

3. Viruses • Contain DNA or RNA –sDNA, dDNA, sRNA, dRNA • Contain 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

4. Viruses Figure 13.1

5. Viruses Figure 13.1

6. Virion Size Figure 13.1

7. Helical Viruses Figure 13.4a–b

8. Helical Viruses Figure 13.4a–b

9. Polyhedral Viruses Figure 13.2a–b

10. Enveloped Viruses Figure 13.3

11. Complex Viruses Figure 13.5a

12. 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.

13. Herpesviridae Herpesvirus Human herpes virus HHV-1, HHV-2, HHV-3 Retroviridae Lentivirus Human immunodeficiency virus HIV-1, HIV-2 Viral Taxonomy

14. Figure 13.6

15. Viruses Figure 13.1

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

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

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

19. 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

20. Virus Identification Figure 13.9

21. 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.

22. 1 2 3 Figure 13.11, steps 1–3, 6–7

23. 4 Figure 13.11, steps 4–5, 8

24. One-Step Growth Curve Figure 13.10

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

26. The Lysogenic Cycle Figure 13.12

27. Specialized Transduction 2 3 4 5 6 Figure 13.13

28. Multiplication of Animal viruses • Attachment: Viruses attach 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.

29. Multiplication of Animal viruses

30. Multiplication of Animal viruses

31. Multiplication of Animal viruses

32. Multiplication of Animal viruses

33. PERSISTANCE VS. LATENT INFECTIONSs

34. PERSISTANCE VS. LATENT INFECTIONSs

35. PRIONS • Infectious Proteins

36. VIROIDS • Infectionus RNA • Plant diseases so far