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VIRUSES, V IR O IDS A ND

PRIONS

Chapter 13



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



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.



Plaque Method

Each plaque originates

with a single viral

particle. The concentration of

viruses is given as

plaque forming units

or PFU.


http://slidepdf.com/reader/full/virus-viroid-gate 7/20Figure 13.7

Growing Animal Viruses in the

Laboratory

Animal viruses

may be grown

in livinganimals or in

embryonatedeggs


http://slidepdf.com/reader/full/virus-viroid-gate 8/20Figure 13.8


Laboratory Animal and plant viruses may be grown in

cell culture

Continuous cell lines may be maintained

indefinitely




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.



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



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



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



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



Table 13.5



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



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



Avian Influenza

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