Viruses, Viroids, & Prions - Mrs. Buck's Web...

VIRUSES, VIROIDS, &

PRIONS

VIRUSES A .K .A . OBLIGATE INTRACELLUL AR PARASITES

• Discovery

– Louis Pasteur (1884)

• Suggests something smaller than BacT is causing rabies

• Uses the word VIRUS: latin for poison

– Dimitri Ivanowski (1892)

• Studying Tobacco Mosaic Disease

• Notes when infected extract was filtered to remove bacteria the

extract continues to cause disease

– 20th century development of electron microscopy leads to visibility of

viruses


• Classification

– International Committee on Taxonomy of Viruses

• Uses taxonomic levels

• Order-Family-Genus-Species

– 2,500 different species of viruses have been identified

• There can be subtypes within a species

– based on types of glycoproteins

• Ex. H5N1 is bird flu and H1N1 is swine flu


• Stucture

– Size: 10-400 nm.

– Categorized based on:

• Size & Shape

– Threadlike to Polyhedral

– Outer capsid w/protein subunits and an inner nucleic acid core

• Type of Nucleic Acid

– Single or double stranded

• Presence or Absence of Outer Envelope

Capsid (protein)

Covering

Envelope (not in all viruses)

Virus

Nucleic Acid (DNA/RNA)

Inner Core

Various Proteins (enzymes)


• Reproduction

– Must infect a living cell

• hijack the cells protein synthesis machinery

– Host specific

• Infects specific organisms or tissues

– Ex. Tobacco Mosaic Virus (Tobacco), HIV (blood), Polio(nerve), Hepatitis(liver)

– Reproduction Cycle

• Attachment: Virus binds to specific Host cell

• Penetration: cell engulfs virus (endocytosis) or virus injects genome into cytoplasm

• Biosynthesis: new viral parts (capsid, subunits, spikes, genome) made by host cell

• Maturation: new viruses assembles from newly produced parts

• Release: new viruses exit= lysis or budding & infect new host cells


• Variations in Reproduction

– Bacteriophages (virus that infects a bacterium)

• Lytic Cycle (5 steps)

• Lysogenic Cycle: latent phase

– Viral DNA (prophage) is integrated into BacT DNA and passed on in cell division

– Animal viruses

• Similar alternating life cycle to bacteriophages

• Introduce genetic material by fusion of spike studded envelope w/ host cell membrane

(endocytosis)

– Virulent viruses

• Enter directly into lytic cycle and rapidly destroy host cells

– Retroviruses

• Animal Viruses w/ RNA genome

• Converted to DNA by the host cell using reverse transcriptase & integrated into host DNA

VIROIDS & PRIONS • Viroids

– Naked strands of RNA (not covered by a capsid)

– Must infect a host cell to reproduce

• Prions

– Proteinaceous infectious particles

– When in contact with prion a normal protein will change shape altering

function

– TSEs transmissible spongiform encephalopathies: due to prions

• Mad cow disease

• All TSEs are fatal

E M E R G I N G V I R U S E S

A I D S / H I V

W E S T N I L E E N C E P H A L I T I S

H A N TA V I R U S P U L M O N A RY S Y N D R O M E

S E V E R E A C U T E R E S P I R ATO RY S Y N D R O M E ( S A R S )

E B O L A H E M O R R H A G I C F E V E R

AV I A N I N F L U E N Z A H 5 N 1

S W I N E F L U H 1 N 1

N OV E L C O R O N AV I R U S

Viruses, Viroids, & Prions - Mrs. Buck's Web...

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