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