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Ch 18 Microbial Models: Genetics of Viruses and Bacteria.

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Presentation on theme: "Ch 18 Microbial Models: Genetics of Viruses and Bacteria."— Presentation transcript:

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3 Ch 18 Microbial Models: Genetics of Viruses and Bacteria

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

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

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

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

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

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

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

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16 Lytic Cycle

17 “lock & key”

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

19 Lytic Cycle phage DNA hydrolysises bacterial DNA via. enzymes

20 Lytic Cycle phage proteins are produced, phage DNA reproduced

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

22 Lytic Cycle Lysozyme produced and bacterial wall is digested

23 Lytic Cycle

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25 Lysogenic Cycle

26 temperate viruses Lysogenic Cycle temperate viruses

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

28 encorporate into bacterial DNA via. crossing over encorporate into bacterial DNA via. crossing over Lysogenic Cycle

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

30 at some point, exits the chromosome, & initiates a LYTIC cycle Lysogenic Cycle

31 Phages manufactured Lysogenic Cycle Phages manufactured

32 virulent latent/ temperate

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

34 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

35 Why haven’t phages exterminated all bacteria? LYSOGENY

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

38 1. membranous envelope p resent 2. membranous envelope a aa absent Viruses are Classified as :

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

40 ex. Herpes Simplex Type 1 (cold sore)

41 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.

42             

43 RETROVIRUS ex. HIV

44 human immunodificiency virus

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

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

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

49 LAST KIND DNA

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

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

53 “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!

54 EMERGING VIRUSES: HOW? HOW?HOW? HOW? Mutations of existing virus

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

56 Mutated form spread from animals

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

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

59 Some viruses cause

60 Human papilloma virus

61 Viral nucleic acid becomes integrated into the hosts DNA

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

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

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

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

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