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Published byPaul Stokes Modified over 8 years ago
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Other biological particles
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Non-cellular infectious agent Characteristics of all viruses 1) protein coat wrapped around DNA or RNA 2) cannot reproduce by itself (not a living thing) 3) rapid replication= rapid evolution new phenotypes/protein coates Virus
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Based on DNA or RNA virus & diseases Based on structure of protein Envelope presence Size ranges: 18nm – 350nm Classification of Viruses
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May have proteins that bind to receptors on host cell May form a sheath and tail fibers that attach to host cell = complex virus Protein Coat (capsid)
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Double stranded DNA Single stranded DNA Double stranded RNA Single stranded RNA Largest containing 4 genes Viral Nucleic Acids
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RNA can be … 1) used as a template to make viral mRNA or 2) copied into DNA by reverse transcriptase = a retrovirus 3) RNA polymerase has no proofreading function so mutates faster than DNA virus RNA Viruses
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1) Attachment – virus chemically recognizes host and locks on 2) Penetration- entire virus or virus DNA/RNA enters host cell 3) Replication & protein synthesis of Viral genes makes viral proteins and DNA/RNA 4)Assembly – new viruses put together 5) Release – new viruses leave host cell Viral Multiplication Steps ( component assembly model)
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Steps proceed rapidly and end in lysing of cell Lytic pathway
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Viral DNA integrated into host DNA Viral DNA copied each time host cell divides Latent period = no symptoms but more and more host cells are becoming infected Stimulus causes switch to lytic cycle and symptoms appear (Type I Herpes simplex ) cold sores Latent infection can give traits to host cell (Increased pathogenicity in bacteria) Lysogenic Pathway
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Are wrapped in a layer of host cell membrane Intermembrane viral glycoproteins protruding out of membrane bind to host cell Protovirus DNA integrates into host DNA New viruses can leave host cell without lysis. Enveloped Viruses
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HIV virus binds to cellular receptors on white blood cells called T-cells. T-cells are immune cells Protovirus integrates into T-cell DNA We can not get to the protovirus so we can not cure aids HIV = enveloped retrovirus
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Viral proteins mutate rapidly Different viruses in same host can combine genetic information New shots needed for common quickly mutating viruses. Viral protein mutation
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Transduction Bacterial genes transferred from one bacteria to another via virus particles
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normal prions =proteins in nervous tissue Infectious prions are misfolded prions Misfolded prions deposit in brain Misfolded prions can cause normal prions to misfold Infectious Prions not destroyed by cooking! Infectious Prions
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Mad cow disease = BSE (bovine spongiform encephalopathy) Beef infected with BSE can cause vCDJ in humans Don’t eat cow brains or spinal tissues! Mad Cow!
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