1. Viruses, Viroids, & Prions
Avg. person catches a cold 2 to 3 times per year

2. Viruses A.K.A. Obligate Intracellular 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
Viruses do not fossilize so their origin and evolutions is difficult to study

4. Viruses A.K.A. Obligate Intracellular Parasites
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

6. Viruses A.K.A. Obligate Intracellular Parasites
Stucture
Size: 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)

7. Complex- helical-spherical

8. Viruses A.K.A. Obligate Intracellular Parasites
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
*Match between virus surface molecules/proteins and host cell receptors
*Uses host cells ribosomes, enzymes, tRNA molecules, and energy ATP

10. Viruses A.K.A. Obligate Intracellular Parasites
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
When bacT has the prophage it produces a toxin: ex strep throat becomes scarlett fever
Ebola: 90% of those infected die w/in 2-21 days
HIV enters the lysogenic cycle and can lie latent for many years
AZT is a antiretroviral drug that interferes with the function of reverse transcriptase

13. 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

14. Emerging Viruses Aids/HiV West nile encephalitis
Hanta virus pulmonary syndrome
Severe acute respiratory syndrome (sars)
Ebola hemorrhagic fever
Avian influenza h5n1
Swine FluH1n1
Novel coronavirus
Create slide presentation to teach the class about your virus:
Discovery, classification, structure, reproduction, symptoms, treatments