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Microbial Models: Genetics of Viruses and Bacteria
Ch 18 Microbial Models: Genetics of Viruses and Bacteria
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smaller than ribosomes!
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S.A.R.S. HIV Ebola Polio Bird Flu Meningitis chicken pox
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Virus- *biological particle (not a cell)
*composed of nucleic acid (RNA or DNA)
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Virus- *surrounded by capsid (protein coat) and sometimes a viral envelope (membrane surrounding)
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The head of a dress-maker's pin can provide seating accommodation for five hundred million rhinoviruses (cause of the common cold) !
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Why not alive? Lacks: nucleus, cytoplasm, organelles, cell membrane
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obligate intracellular parasites
Why not alive? No reproduction by mitosis No meiosis (require a host cell in order to reproduce) obligate intracellular parasites
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resistant to dehydration by osmosis obligate intracellular parasites
Why not alive? Resistant to alcohol resistant to dehydration by osmosis obligate intracellular parasites
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cells cannot form crystals obligate intracellular parasites
Why not alive? virus crystallization cells cannot form crystals obligate intracellular parasites
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Reproduction: 3 ways:
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Lytic Cycle
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Lytic Cycle “lock & key”
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Lytic Cycle phage injects DNA
(hopefully, for the virus, it is resistant to the restriction nucleases!)
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Lytic Cycle phage DNA hydrolysises bacterial DNA via. enzymes
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Lytic Cycle phage proteins are produced, phage DNA reproduced
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Lytic Cycle host cell provides: nucleotides, ribosomes, tRNA etc.
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Lytic Cycle Lysozyme produced and bacterial wall is digested
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Lytic Cycle BOOM!!
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Lytic Cycle virulent virus
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Lysogenic Cycle
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Lysogenic Cycle temperate viruses
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Lysogenic Cycle “phage” inserts DNA; via. “lock & key”
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Lysogenic Cycle encorporate into bacterial DNA via. crossing over
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cellular division w/ a “friend” -replicates along with bacterial DNA)
Lysogenic Cycle cellular division w/ a “friend” -replicates along with bacterial DNA)
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Lysogenic Cycle at some point, exits the chromosome, & initiates a LYTIC cycle
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Lysogenic Cycle Phages manufactured
BOOM!!
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latent/ temperate virulent
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Why haven’t phages exterminated all bacteria?
Restriction Enzymes in bacteria Methylation of bacterial DNA prevents the restriction enzyme from attacking its own self
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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
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Why haven’t phages exterminated all bacteria?
LYSOGENY
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variations of viral reproduction
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Viruses are Classified as:
1. DNA viruses 2. RNA viruses
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Viruses are Classified as:
1. membranous envelope present 2. membranous envelope absent
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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
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ex. Herpes Simplex Type 1 (cold sore)
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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.
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does not kill host Viral Envelope
Viral Envelope
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RETROVIRUS ex. HIV
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human immunodificiency virus
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HIV `
HIV ` host is a WBC called a T-cell
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HIV needs to connect to TWO protein types on the outside of the Immune System’s Helper T Cells
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HIV needs to connect to TWO protein types on the outside of the Immune System’s Helper T Cells (WBC)
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LAST KIND DNA
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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
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viral DNA replicated uses it to enter host DNA capsid removed genetic material duplicated
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Viral Diseases Measles Polio Smallpox Influenza S.A.R.S. Bird flu
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-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!
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Mutations of existing virus
EMERGING VIRUSES: HOW? HOW?HOW? HOW? BIRD FLU... where did we get it? Mutations of existing virus
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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
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Mutated form spread from animals
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How to combate Virus? VACCINES - -*variants of pathogen
*stimulates the immune system to “arm” and “defend”
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Note: Can prevent some viral illnesses, Cannot cure the viral infection
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Some viruses cause Cancer
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Human papilloma virus
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Viral nucleic acid becomes integrated into the hosts DNA
Cancer
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Proto-oncogenes code for proteins that affect the cell cycle.
Cancer
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Viroid- “naked” RNA *disrupt metabolism of plants stunts growth
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Viroid- BIG NEWS b/c *molecules* can be an infectious agent and spread disease!
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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
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