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http//www.cellsalive.com/howbig.htm
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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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• Why not alive?
• No reproduction by mitosis No meiosis ?

• (require a host cell in order to reproduce)

obligate intracellular parasites
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• Why not alive?
• Resistant to alcohol ?

• resistant to dehydration by osmosis

obligate intracellular parasites
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• 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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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 havent 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 havent 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 havent 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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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
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Viral Envelope
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RETROVIRUS ex. HIV
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human immunodificiency virus
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?
HIV

host is a WBC called a T-cell
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http//www.youtube.com/watch?vB7ITZgag6w0feature
related http//www.youtube.com/watch?vdyxujBKHdW
c http//www.youtube.com/watch?v9leO28ydyfUNR1

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HIV needs to connect to TWO protein types on the
outside of the Immune Systems Helper T Cells
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HIV needs to connect to TWO protein types on the
outside of the Immune Systems 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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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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EMERGING VIRUSES HOW? HOW?HOW? HOW?
BIRD FLU...
where did we get it?
Mutations of existing virus
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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 converts regular
  proteins to prion version Mad cow disease

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