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8/3/2019 Virus Viroid Gate
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VIRUSES, V IR O IDS A ND
PRIONS
Chapter 13
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Multiplication of Animal Viruses
Attachment: Viruses attach to cell membrane
Penetration by endocytosis or fusion
Uncoating by viral or host enzymes Biosynthesis: Production of nucleic acid and
proteins
Maturation: Nucleic acid and capsid proteins
assemble Release by budding (enveloped viruses) or
rupture
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Attachment, Penetration, Uncoating
By fusion
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Budding of an Enveloped Virus
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Growing Bacteriophages in the
Laboratory Plaque method is used to measure viral
number.
Mix bacteriophages with host bacteria and
nutrient agar.
After several viral multiplication cycles, the
bacteria in the area surrounding the originalvirus are destroyed; the area of lysis is
called a plaque.
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Plaque Method
Each plaque originates
with a single viral
particle. The concentration of
viruses is given as
plaque forming units
or PFU.
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Growing Animal Viruses in the
Laboratory
Animal viruses
may be grown
in livinganimals or in
embryonatedeggs
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Growing Animal Viruses in the
Laboratory Animal and plant viruses may be grown in
cell culture
Continuous cell lines may be maintained
indefinitely
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Growing Animal Viruses in the
Laboratory
Primary cell lines can be used; however,
these cell lines remain viable for only short
periods of time.
Continuous cell lines may be maintained
indefinitely.
Continuous cell lines are transformed(cancerous) such as HeLa (HenriettaLacks) cells are a commonly used cellline.
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Virus Identification
1. Cytopathic effects2. Serological tests
Detect antibodies against viruses in a patient
Use antibodies to identify viruses inneutralization tests, viral hemagglutination, and
Western blot
3. Nucleic acids
RFLPs (Restr iction fragment lengthpolymorphism)
PCR
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Viruses and Cancer
Activated oncogenes transform normal cells
into cancerous cells
The genetic material of oncogenic viruses
becomes integrated into the host cell's DNA
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Oncogenic Viruses
Oncogenic DN Aviruses
Adenoviridae
Herpesviridae
Poxviridae
Papovaviridae
Hepadnaviridae
Oncogenic RN Aviruses
Retroviridae
Viral RNA istranscribed to DNA,
which can integrate
into host DNA
HTLV-1
HTLV-2
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Latent and Persistent Viral Infections
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Virus remains inasymptomatic
host cell for
long periods Herpes virus
Cold sores
VaricellaZoster
chicken pox and
shingles
Latent Viral Infections
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Disease process occurs
over a long
period; Table 13.5
Persistent Viral Infections
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Table 13 5
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Prions
Pro teinaceous In fectious particle
Inherited and transmissible by ingestion,
transplant, and surgical instruments
Spongiform encephalopathies: Sheep scrapie,
C reutzfeldt-Jakob disease, fatal familial
insomnia, kuru, mad cow disease
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Prions
PrPC: Normal cellular prion protein, on cell
surface
PrPSc: Scrapie protein; accumulates in braincells, forming plaques
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Plant Viruses and Viroids
Viroids:Infectious
RNA; e.g.,
potato spindletuber disease