viruses sbi 3c – grade 11 college biology. bacteria vs. viruses let’s investigate! e. coli...
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VirusesVirusesSBI 3C – Grade 11 College BiologySBI 3C – Grade 11 College Biology
Bacteria vs. Viruses
Let’s investigate!
http://learn.genetics.utah.edu/content/begin/cells/scale/
E. coli O157:H7
Responsible for 1% of food borne illnessCauses 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: 100-300 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?
http://www.youtube.com/watch?v=zGSSDJhHgp0&NR=1
French-Canadian MicrobiologistFirst to see bacteriophage lysis E. coli in 1917Phage 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
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?
Viruses: What do we need to know?
Method of TransmissionMethod 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 - VirusesSBI 3C - VirusesPresented By Joyce LongfieldPresented By Joyce Longfield