Viruses SBI 3C – Grade 11 College Biology

Bacteria vs. Viruses Let’s investigate! E. coli O157:H7 Responsible for 1% of food borne illness Causes bloody diarrhea Can be lethal Antibiotic resistant ……….but not T4 Phage resistant!

Bacteria vs. Viruses Viruses (“poison”) Intracellular Parasite Host specific Bacteriophage (“Bacteria Eater”) – viruses specific to infecting bacteria Phage T4 Head Protein Sheath Tail Fibers

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) E. coli O157:H7 1 min - Host DNA, RNA and protein synthesis is turned off

Viral Transcription & Translation E. coli O157:H7 2 min – viral mRNA synthesis begins 3 min – bacterial DNA begins to breakdown

Viral Assembly E. coli O157:H7 5 min – Phage DNA synthesized 12 min – completed heads and tails appear

Viral Assembly E. coli O157:H7 15 min – complete Phage particles appear

Bacterial Lysis: Phages Released E. coli O157:H7 22 min – cell lysis and Phage release

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? 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 re- infect 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

LivingNon-living ReplicateNo metabolism EvolveNo 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