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Viruses SBI 3C – Grade 11 College Biology Bacteria vs. Viruses Let’s investigate! http://learn.genetics.utah.edu/content/begin/cells/scale/ Responsible for 1% of food borne illness Causes bloody diarrhea Can be lethal Antibiotic resistant ……….but not T4 Phage resistant! E. coli O157:H7 Bacteria vs. Viruses Viruses (“poison”) Intracellular Parasite Host specific Head Bacteriophage (“Bacteria Eater”) – viruses specific to infecting bacteria Protein Sheath Tail Fibers Phage T4 Virus Types Characterized by: 1. Genome: DNA or RNA, Single Stranded or Double Stranded, Linear or Circular 2. Capsid or Envelope Virus Sizes T4 Genome Size Virus Attachment E. coli O157:H7 Viral Penetration & Uncoating (disassembly) 1 min - Host DNA, RNA and protein synthesis is turned off E. coli O157:H7 Viral Transcription & Translation 2 min – viral mRNA synthesis begins 3 min – bacterial DNA begins to breakdown E. coli O157:H7 Viral Assembly 5 min – Phage DNA synthesized 12 min – completed heads and tails appear E. coli O157:H7 Viral Assembly 15 min – complete Phage particles appear E. coli O157:H7 Bacterial Lysis: 100-300 Phages Released 22 min – cell lysis and Phage release E. coli O157:H7 Viral Replication Summary Step 1 – A&P: Attachment & Penetration Step 2 – U: Uncoating – viral nucleic acid available for transcription Step 3 – R: Replication of Phage DNA & protein synthesis Step 4 – A&R: Assembly & Release Viral Lytic Cycle vs Lysogenic 22 minutes?! – How do we know? http://www.youtube.com/watch?v=zGSSDJhHgp0&NR=1 French-Canadian Microbiologist First to see bacteriophage lysis E. coli in 1917 Phage therapy was a successful method of treatment until 1928 …….Why??? Felix d’Herelle Virus History 1200 B.C. Pharaoh Siptah had Polio 1151 B.C. Ramses V died – his sarcophagus shows pockmarks from Smallpox virus 1892 A.D. Viruses first identified in Tobacco *First time the word “virus” used Virus Evolution Theory – evolved from host genome during genetic events (e.g. genetic mutations, genome rearrangement, gene acquisition, creation, deletion, as well as recombination and translation events) Co-evolve with host ……..but must be faster than the host Needs a host to survive, but beneficial to cross-over to a new host (e.g. animal virus into human) Some viruses overcome host immune memory by mutating to reinfect its host ……..RNA viruses are good at this e.g. HIV mutates so fast the immune system can never clear itself from the body so vaccines end-up failing Viruses: What do we need to know? Living Non-living Replicate No metabolism Evolve No respiration Need a host to survive Does it really matter??? Viruses: What do we need to know? Method of Transmission Method of Prevention Viruses: What do we need to know? Antiviral Drugs – target viruses at various stages in replication (A&P, U, R or A&R) Phage Therapy – back on the rise as an alternative to antibiotics and in treating plant-based bacterial diseases SBI 3C - Viruses Presented By Joyce Longfield