1. Chapter 6 Topics Structure Classification Multiplication
Cultivation and replication
Nonviral infectious agents
Treatment

2. Structure
Size and morphology
Capsid
Envelope
Complex
Nucleic acid

3. The size of viruses compared to yeast, bacteria, and the molecular protein hemoglobin.
Fig. 6.1 Size comparison of viruses with a eucaryotic cell
and bacteria.

4. Negative staining, positive staining, and shadow casting are methods of viewing viruses.
Fig. 6.2 Methods of viewing viruses

5. There are two major structures of viruses called the naked nucleocapsid virus and the enveloped virus.
Fig. 6.4 Generalized structure of viruses

6. Capsid Protective outer shell that surrounds viral nucleic acid
Capsid spikes
Composed of capsomer subunits
Two types of capsids
Helical
Icosahedral

7. Helical capsid Naked helical virus Enveloped helical virus
Ex. Tobacco mosaic virus
Nucleocapsid is rigid and tightly wound into a cylinder-shaped package
Enveloped helical virus
Ex. Influenza, measles, rabies
Nucleocapsid is more flexible

8. Helical capsids have rod-shaped capsomers that form hollow discs that resemble a bracelet.
Fig. 6.5 Assembly of helical nucleocapsids

9. Comparison between a naked helical plant virus and an enveloped helical human virus.
Fig. 6.6 Typical variation of viruses with helical Nucleocapsids.

10. Icosahedron capsid
Three-dimensional, 20-sided with 12 evenly spaced corners
Variation in capsomer number
Polio virus 32 capsomers
Adenovirus 240 capsomers

11. The structure and formation of an adenovirus.
Fig. 6.7 The structure and formation of an icosahedral virus.

12. Icosahedral viruses can be naked or enveloped.
Fig. 6.8 Two types of icosahedral viruses

13. Envelope Lipid and proteins Envelope spikes
During release of animal viruses, a part of the host membrane is taken
Enable pleomorphic shape of the virus
Spherical
filamentous

14. Function of the capsid/envelope
Protect nucleic acid from the host’s acid- and protein-digesting enzymes
Assist in binding and penetrating host cell
Stimulate the host’s immune system

15. Complex viruses
Structure is more intricate than helical and icosahedral viruses
Pox virus
Several layers of lipoproteins
Course surface fibrils
Bacteriophage
Polyhedral head
Helical tail
Fibers for attachment

16. `
Fig Detailed structure of complex viruses

17. Comparison of the morphology (helical, icosahedral, complex) of a naked virus, enveloped virus and a complex virus.
Fig. 6.9 Morphology of viruses

18. Nucleic acid Viruses contain either DNA or RNA
Possess only the genes to invade and regulate the metabolic activity of host cells
Ex. Hepatitis B (4 genes) and herpesviruses (100 genes)
No viral metabolic genes, as the virus uses the host’s metabolic resources

19. Examples of medically important DNA viruses.

20. Examples of medically important RNA viruses.

21. Classification Structure Chemical composition Genetic makeup
Host relationship
Type of disease

22. Three orders of viruses have been developed for classification.
Table 6.4 Examples from the three orders of viruses.

23. Classification of important human viruses.
Table 6.5 Important human virus families, genera, common names, and types of viruses.

24. Multiplication Adsorption Penetration Uncoating Synthesis Assembly
Release

25. Adsorption to the host cell of a enveloped spike virus and naked capsid spike virus.
Fig The mode by which animal viruses adsorb to the host cell membrane

26. Penetration of animal viruses occur by endocytosis or fusion between the viral envelope and the the host cell membrane.
Fig Two principal means by which animal viruses penetrate.

27. Uncoating and synthesis of viruses rely on the host’s metabolic systems.
Fig General feature in the multiplication
cycle of an enveloped animal virus.

28. A mature virus can obtain an envelope by budding off the host cell.
Fig Maturation and release of enveloped viruses

29. Cytopathic effects Damage to the host cell due to a viral infection
Inclusion bodies
Syncytia
Chronic latent state
Transformation

30. Examples of syncytia and inclusion bodies.
Fig Cytopathic changes in cells and cell
cultures infected by viruses

31. Bacteriophage Bacterial virus
Multiplication is similar to animal viruses except for the penetration (inject DNA), release (lyses) and prophage (lysogeny) stages

32. T-even bacteriophage penetrate the host cell by specifically binding and injecting their DNA into the host cell.
Fig Penetration of a bacterial cell by a T-even bacteriophage.

33. After viral multiplication inside the host cell, viral enzymes will weaken the host cell membrane, rupture the cell (lyses), and release numerous virions.
Fig A weakened bacterial cell, crowed with viruses.

34. Lysogeny is when the bacteriophage can insert its DNA into the bacterial host genome.
Fig The lysogenic state in bacteria

35. Comparison of bacteriophage and animal virus multiplication.
Table 6.7 Comparison of bacteriophage and animal virus multiplication.

36. Cultivation and Replication
In vivo methods
Laboratory animals
Embryonic bird tissues
In vitro methods
Cell or tissue culture

37. The early developing bird embryo contains a protective case, providing an ideal environment for viral propagation.
Fig Cultivating animal viruses in a developing
bird embryo

38. A monolayer of monkey kidney cells is a cell culture enabling the propagating viruses.
Fig Appearance of normal and infected cell cultures

39. Noncellular Infectious Agents
Prions
Satellite viruses
Viroids

40. Prions Protein particle with no nucleic acid, no envelope, no capsid
Diseases
Creutzfeldt-Jakob
“mad cow disease”

41. Satellite viruses Dependent on other viruses for replication
Ex. Delta agent, which is only expressed in the presence of hepatitis B virus

42. Viroids Plant pathogens 1/10th the size of normal viruses
Tomatoes, potatoes, cucumbers.
1/10th the size of normal viruses
Naked strands of RNA, no capsid