1. Chapter 13 187 Characterizing and Classifying Viruses, Viroids, and Prions
In 1892, Dmitri Ivanowski discovered tobacco mosaic virus (TMV).
Frederick W. Twort in 1915, and Felix d’Herelle in 1917, indepdently discovered bacteriophage. The agent caused bacterial lysis, known as Twort-d’Herelle phenomenon.

2. 187 Characteristics of Viruses Submicroscopic Filterable
Contain either DNA or RNA, never both
Contain no enzyme systems
Contain no cellular organelles
Obligate intracellular parasites

3. 187
Genome: Capsid: Nucleocapsid Capsomers (capsomeres): Protomers: Peplomers (spikes): Virion:

4. Virions, complete virus particles
Figure 13.1

5. 188 Shapes of Viruses Helical: Polyhedral: Complex: Filamentous:
Tobacco mosaic virus (TMV)
Polyhedral:
Herpes viruses
Adenoviruses (icosahedron viruses)
Complex:
All enveloped viruses (cowpox, rabies, arboviruses)
Filamentous:
Ebola, Marburg, Granulosis virus (insects)

6. Enveloped viruses
Figure 13.7

7. The complex shape of bacteriophage T4
Figure 13.6

8. Fig. 6.6.b

9. Basic types of viral morphology:

12. 189
Classification of Viruses: Based on their structure, chemical composition and genetic makeup: 7 families of DNA viruses 15 families of RNA viruses

14. Contd.

15. 189 Replication of Viruses: 1. Attachment (Adsorption) 2. Penetration
Injection
Endocytosis (phagocytosis or viropexis)
Fusion
3. Eclipse phase
4. Replication
5. Assembly and maturation
6. Release
Lysis
Budding
Exocytosis

16. Fig b

21. Three mechanisms of entry of animal viruses
Figure 13.12

22. The process of budding in enveloped viruses
Figure 13.14

23. 190 Life Cycles: Lytic cycle: The host cell is destroyed by the virus.
The virus is known as the virulent virus
(phage).

24. The lytic replication cycle in bacteriophage
Figure 13.8

25. The lysogenic replication cycle in bacteriophages
Figure 13.11

26. 190
Lysogenic cycle:
Lysogeny is a process in which the viral DNA and the host DNA are joined together. The integrated viral DNA is known as the prophage or provirus. Both the cell and the virus can survive. The virus that carries out this type of life cycle is known as the temperate phage or avirulent phage.

27. Viral Replication
Animation: Viral Replication: Temperate Bacteriophages

28. 191
Replication of : dsDNA dsDNA assembled into dsDNA viruses mRNA Proteins Hepatitis B virus, herpesviruses, papillomaviruses and adenoviruses

29. 192 ssDNA ssDNA dsDNA assembled into ssDNA viruses mRNA Proteins
Parvoviruses (gastroenteritis), satellite viruses and insect viruses

30. 192 Minus (-) Plus (+) strand strand RNA RNA
Plus (+) strand assembled into
RNA Proteins strand
RNA viruses
Picornaviruses (poliovirus, coxsackievirus), coronaviruses (common cold virus) and hepatitis A virus

31. 192
Minus (-) strand RNA Minus (-) assembled Strand RNA Plus (+) strand into – strand RNA RNA viruses Proteins Influenza virus, mumps virus and rabies virus

32. 193
Plus (+) strand RNA Protein Minus (-) strand RNA assembled dsRNA into dsRNA viruses Plus (+) strand RNA dsRNA Minus (-) strand RNA Rotavirus, Colorado tick fever virus

33. 193 reverse RNA DNA RNA assembled into mRNA Proteins RNA viruses
transcriptase
RNA DNA RNA
assembled into
mRNA Proteins RNA viruses
Retroviruses: HIV, HTLV-1, HTLV-2

34. 193-194 Roles of Viruses in Cancer
DNA oncogenic viruses:
Papilloma viruses: wart and cervical cancer
Epstein-Barr virus: Burkitt’s lymphoma
Herpes simplex type II: cervical cancer
Hepatitis B virus: liver cancer
Adenoviruses: respiratory, enteric and eye infections

35. Figure 13.16 The oncogene theory of the induction of cancer in humans.

36. 194 RNA oncogenic viruses: HTLV-I: adult T-cell leukemia
HTLV-II: hairy-cell leukemia

37. 194 Culturing Viruses in the Laboratory:
Cell culture or tissue culture
Primary tissue culture
Continuous tissue culture
2. Culturing viruses in bacteria
3. Culturing viruses in plants and animals
Culturing viruses in embryonated chicken
eggs

38. Fig c
Plaque formation on the lawn of E. coli.

39. Fig. 6.21
Inoculation of chick embryos.

40. 194
Monolayer: Hela cell line: Plaque: Plaque-forming unit (PFU): Cytopathic effect (CPE):

41. Cytopathic changes in animal cells.

42. 195
Viroids: single-stranded or double-stranded RNA, no protein coat, nucleotides, infect plants causing: potato spindle tuber disease citrus exocortis chrysanthemum stunt cucumber pale fruit disease cadang cadang in coconuts

43. One effect of viroids on plants
Figure 13.21

44. Characteristics of Prions
Infectious protein particles that cause neurological diseases
Contain no DNA or RNA
Cannot be digested by nucleases
Can be digested by proteolytic enzymes
Resistant to radiation
Resistant to high temperture up to 90oC

45. 195 Diseases Caused by Prions: Kuru disease Creutzfeldt-Jakob disease
Scrapie of sheep
Chronic wasting disease (CWD) in deer and elk
Mad cow disease

46. Formation of Prions Two types of Prions:
1. PrPC : is the normal cellular prion protein
Made by all mammals
Normal structure with -helices called cellular PrPC
2. PrPSc: (PrPSc stands for scrapie prion protein). It is
the disease-causing form with -sheets.
The PrPSc converts cellular prion protein (PrPC) into the disease-causing form PrPSc by inducing conformational change.

47. Other Parasitic Particles: Viroids and Prions
Animation: Prions: Characteristics

48. Fig. 6.22
Mad cow disease (bovine spongiform encephalopathy) caused by prions.

49. 196
Satellite viruses: These are defective viruses that require a helper virus in order to replicate. Examples: Adeno-associated virus (AAV) requires adenovirus. Delta agent requires hepatitis B virus.