viruses lecture.pptx
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VIRUSESIRUSES
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Smallest to largest..Prions
Viruses
BacteriaFungi
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PrionsInfectious proteinNo DNA or RNANormal cellular form of protein vs.pathological form
Pathological form
found in neuraltissue and tonsils
PrP-C & PrP-Sc
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PathologySpongiform
encephalopathy:transmissible,familial
Transmission: oral,operative (neuraltissue, dura,corneas), ???
bloodResistance to
disinfectantsFormaldehyde
increases
infectivity
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VirusesNon-cellular
No cellular composition
Do not grow or metabolize organic materials
Produce no waste products
Do not utilize energy
Do not adapt to their environment
Reproduce only within living cells (cannotreproduce on their own)
Size range from 20 nm (polio virus) to 300 nm(pox virus)
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Figure 18.1 Comparing the size of a virus, a bacterium, and a eukaryotic cell
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Viral ShapesIcosahedral I.M., mumps, chicken pox and
herpes simplex
Helical rabies and tobacco mosaic virus
Box shape coxpox and small pox
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Figure 18.2 Viral structure
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The Structure Of a Virus
Viruses arecomposed of acore of nucleic
acidThe Nucleic acid
core is surroundedby a protein coat
called a capsidThe Nucleic core is
either made up ofDNA or RNA butnever both
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Viruses
Composed of genome in a capsidDNA or RNA
Shell of protein (capsid) surrounding nucleicacid
Capsid is composed of repeating units of
capsomeres (proteins)
Envelope, spike
Classification on basis of nucleic acid
DNA viruses: eg Herpes simplexvirus (HSV)
RNA viruses: eg influenza virus
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DNA viruses: herpes simplex virus (HSV)
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RNA viruses: Influenza
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CapsidCapsidFunctions
Protection of NAAttachment for
naked viruses
Enzyme
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EnvelopeEnvelope
AttachmentEntry
Assembly- matrixproteins
ReleaseProteins are viral
Lipids are host If the membrane envelope is
destroyed, the virus becomesnoninfectious. Why?
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Bacteriophages attack
bacteria (prokaryotes)viruses attack eukaryotic
cells.
Viruses and bacteriophages invade
cells and use the host cell'smachinery to synthesize more oftheir own macromolecules.
Once inside the host the
bacteriophage or virus will eithergo into a Lytic Cycle-
destroying the host cellduring reproduction.
or
It will go into a Lysogenic Cycle- a
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Viral effects on host cells
Degeneration (cytopathic effect): CMV
Cell lysis
Cell fusion, syncytia formation: RSV
Cell proliferation
Transformation: malignancy (parvoviruses)
Latent infection - no sign of infection until
reactivation
cold sores (HSV) chickenpox shingles (VZV)
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Mode of Attack
DNA to mRNA to Ribosomes tomake new viruses
RNA to Ribosomes to make new
viruses
Result the cell dies
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HIV is a retrovirus injecting the enzyme, reversetranscriptase into the cell to copy viral RNA intoDNA.
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iru se s a re h o st sp e cific a p ro te in o n th e su rfa ce o f th e v ir
a s a sh a p e th a t m a tch e s a m o le cu le in th e p la sm a m e m b ra
, .f its h o st a llo w in g th e viru s to lo ck o n to th e h o st ce ll
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HIV doesnt target just any cell, it goes right for thecells that want to kill it. Helper" T cells are HIV'sprimary target. These cells help direct the immune
system's response to various pathogens.
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PathwaysLytic = RNA or DNA routes
Lysogenic = RNA to DNA to
mRNA to Ribosomes A
reverse route through thecell.
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Figure 18.3 A simplifiedviral reproductive cycle
Figure 18.6 The reproductive cycle of an enveloped virus
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Figure 18.6 The reproductive cycle of an enveloped virus
Figure 18.4 The lytic cycle of phage T4
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Figure 18.4 The lytic cycle of phage T4
Figure 18.5 The lysogenic and lytic reproductive cycles of phage , a temperate phage
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gu e 8 5 e ysoge c a d y c ep oduc e cyc es o p age , a e pe a e p age
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28/34The Lytic Cycle
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VaccinesViruses grown on chicken embryos areattenuated vaccines
Another type of vaccine is made by heatkilling the virus
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CMV hepatitis
owl eye effect inclusion body
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Varicella zoster virus (VZV)
VZV: Chickenpox
VZV: Shingles
Re-activation oflatent infection
Suppression of
cell mediatedimmunity
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Strategy ofreplication
Lytic
Temperate
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