[W2] practical virology Flashcards
(32 cards)
What are three methods used to quantify viruses?
Plaque assays, quantal dose response (LD50), hemagglutination.
What techniques are used to study virus structure?
Electron microscopy, X-ray crystallography, density gradient centrifugation.
How can viruses be detected in a sample?
By detecting viral proteins (serological methods) or viral nucleic acids (qPCR, sequencing).
What is a plaque assay used for?
To measure virus quantity in PFU/mL by counting plaques formed on a bacterial lawn.
What does LD50 represent?
The dose at which 50% of infected organisms die.
What virus model was used in many foundational experiments?
Bacteriophages.
What was the significance of the Hershey and Chase (1952) experiment?
It demonstrated that DNA, not protein, is the genetic material.
What isotopes were used in the Hershey-Chase experiment?
³²P (for DNA) and ³⁵S (for protein).
What did Luria and Delbrück’s fluctuation test prove?
That mutations arise spontaneously, not in response to selective pressure.
What is the key concept of the one-step growth curve by Ellis and Delbrück (1939)?
Virus replication occurs in stages: infection, replication, assembly, and release.
What is the eclipse period in the one-step growth curve?
A phase where no infectious particles are detected as viruses have disassembled and are replicating inside cells.
What defines the rise period in viral replication?
Release of mature virions from the host cell.
How is MOI (Multiplicity of Infection) calculated?
MOI = (total virus particles) / (total host cells).
Does MOI = 1 mean all cells are infected?
No, only ~63% are infected due to the Poisson distribution.
What is the formula for Poisson distribution used in virus infection?
P(n) = (mⁿ × e^(–m)) / n!, where m is the MOI.
How do you calculate the percentage of infected cells?
P(n > 0) = 1 – P(0).
What is burst size?
The number of phage particles produced per infected bacterium, calculated as phage yield (PFU/mL) divided by infected bacteria titre (CFU/mL).
How can the eclipse period be experimentally measured?
By artificially lysing infected cells with chloroform to release intracellular viruses, which are then counted via plaque assay.
What happens during the eclipse period?
Virus particles disassemble after entering the host, viral genome is released, host DNA is degraded, and viral mRNAs/proteins begin synthesis.
What does the intracellular accumulation phase refer to?
The period after the eclipse, when new phages are assembled inside the cell but not yet released.
When do the curves of total and extracellular virus counts merge in a one-step growth curve?
About 40 minutes post-infection, when all cells have lysed.
What does burst size measure and how is it calculated?
It measures phage particles per infected cell: Burst size = (phage yield in PFU/mL) ÷ (infected bacterial titre in CFU/mL).
Why is synchronizing infection important in the one-step growth curve?
It ensures that all host cells are infected simultaneously, allowing replication stages to be observed uniformly.
In MOI calculation, why can’t you use just the titre of the virus stock?
Because MOI depends on the actual number of particles used in the volume added, not just the stock concentration.