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

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

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

Viruses A.K.A. Obligate Intracellular Parasites 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)

Complex- helical-spherical

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

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

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

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