Other biological particles

  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

  Based on DNA or RNA virus & diseases  Based on structure of protein  Envelope presence  Size ranges:  18nm – 350nm Classification of Viruses

  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)

  Double stranded DNA  Single stranded DNA  Double stranded RNA  Single stranded RNA  Largest containing 4 genes Viral Nucleic Acids

  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

  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)

  Steps proceed rapidly and end in lysing of cell Lytic pathway

  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

  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

 Transduction  Bacterial genes transferred from one bacteria to another via virus particles

  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

  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!