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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