2. Microbial Models: Genetics of Viruses and Bacteria
Ch 18
Microbial Models: Genetics of Viruses and Bacteria

3. smaller than
ribosomes!

5. S.A.R.S.
HIV
Ebola
Polio
Bird
Flu
Meningitis
chicken pox

6. Virus- *biological particle (not a cell)
*composed of nucleic acid (RNA or DNA)

7. Virus-
*surrounded by capsid (protein coat) and sometimes a viral envelope (membrane surrounding)

9. The head of a dress-maker's pin can provide seating accommodation for five hundred million rhinoviruses (cause of the common cold) !

10. Why not alive?
Lacks: nucleus, cytoplasm, organelles, cell membrane

11. obligate intracellular parasites
Why not alive?
No reproduction by mitosis No meiosis 
(require a host cell in order to reproduce)
obligate intracellular parasites

12. resistant to dehydration by osmosis obligate intracellular parasites
Why not alive?
Resistant to alcohol 
resistant to dehydration by osmosis
obligate intracellular parasites

13. cells cannot form crystals obligate intracellular parasites
Why not alive?
virus crystallization 
cells cannot form crystals
obligate intracellular parasites

14. Reproduction:
3 ways:

15. Lytic Cycle

16. Lytic Cycle
“lock & key”

17. Lytic Cycle phage injects DNA
(hopefully, for the virus, it is resistant to the restriction nucleases!)

18. Lytic Cycle
phage DNA hydrolysises bacterial DNA via. enzymes

19. Lytic Cycle
phage proteins are produced, phage DNA reproduced

20. Lytic Cycle
host cell provides: nucleotides, ribosomes, tRNA etc.

21. Lytic Cycle
Lysozyme produced and bacterial wall is digested

22. Lytic Cycle
BOOM!!

23. Lytic Cycle
virulent
virus

24. Lysogenic Cycle

25. Lysogenic Cycle temperate viruses

26. Lysogenic Cycle
“phage” inserts DNA; via. “lock & key”

27. Lysogenic Cycle
 encorporate into bacterial DNA via. crossing over

28. cellular division w/ a “friend” -replicates along with bacterial DNA)
Lysogenic Cycle
cellular division w/ a “friend” -replicates along with bacterial DNA)

29. Lysogenic Cycle
at some point,  exits the chromosome, & initiates a LYTIC cycle

30. Lysogenic Cycle Phages manufactured
BOOM!!

31. latent/ temperate
virulent

32. Why haven’t phages exterminated all bacteria?
Restriction Enzymes in bacteria
Methylation of bacterial DNA prevents the restriction enzyme from attacking its own self

33. Why haven’t phages exterminated all bacteria?
Natural Selection favors the mutant bacteria w/ protein receptors that have an altered shape
no longer recognizable by phage

34. Why haven’t phages exterminated all bacteria?
LYSOGENY

35. variations of
viral reproduction

36. Viruses are Classified as:
1. DNA viruses
2. RNA viruses

37. Viruses are Classified as:
1. membranous envelope present
2. membranous envelope absent

38. Envelope derived from nuclear membrane
ex. of enveloped = herpes virus
Reproduce in nucleus
Envelope derived from nuclear membrane
Typically, leave some DNA behind in nerve cells

39. ex. Herpes Simplex Type 1 (cold sore)

40. Herpes Viruses Use nuclear membrane to derive new envelope.
Viral DNA integrated into Host DNA as a provirus.
Shows both lytic and lysogenic life cycles.

41. does not kill host Viral Envelope 

Viral Envelope




42. RETROVIRUS ex. HIV

43. human immunodificiency virus

44. HIV   `
 
HIV `
host is a WBC called a T-cell

46. HIV needs to connect to TWO protein types on the outside of the Immune System’s Helper T Cells

47. HIV needs to connect to TWO protein types on the outside of the Immune System’s Helper T Cells (WBC)

48. LAST KIND
DNA

49. DNA Viruses
1.Insert their DNA into host/ the host produces mRNA compliment 
2.Production of new viral proteins, or join with the DNA of the host cell 
3.Directs production of new viruses

50. viral DNA
replicated
uses it to enter host
DNA
capsid removed
genetic material
duplicated

51. Viral Diseases
Measles
Polio
Smallpox
Influenza
S.A.R.S.
Bird flu

52. -Joshua Lederberg, Ph.D, Nobel laureate 1969
“The single biggest threat to man's continued dominance on the planet is the virus!”
-Joshua Lederberg, Ph.D, Nobel laureate 1969
(won prize with Beadle and Tatum)
Actually, he won the prize for discovering that bacteria can exchange genes… but what a great quote!

53. Mutations of existing virus
EMERGING VIRUSES: HOW? HOW?HOW? HOW?
BIRD FLU...
where did
we get it?
Mutations of existing virus

54. Dissemination from a small, isolated population
Increasing viral traffic ie. new roads can allow virus to spread between previously isolated areas
Dissemination from a small, isolated population

55. Mutated form spread from animals

56. How to combate Virus? VACCINES - -*variants of pathogen
*stimulates the immune system to “arm” and “defend”

57. Note: Can prevent some viral illnesses, Cannot cure the viral infection

58. Some viruses cause
Cancer

59. Human papilloma virus

60. Viral nucleic acid becomes integrated into the hosts DNA
Cancer

61. Proto-oncogenes code for proteins that affect the cell cycle.
Cancer

62. Viroid- “naked” RNA *disrupt metabolism of plants stunts growth

63. Viroid-
BIG NEWS b/c *molecules* can be an infectious agent and spread disease!

64. Prions- infectious. present in brain cells. misfolded proteins
Prions- infectious *present in brain cells *misfolded proteins *converts “regular” proteins to prion version Mad cow disease