[W2] practical virology Flashcards

(32 cards)

1
Q

What are three methods used to quantify viruses?

A

Plaque assays, quantal dose response (LD50), hemagglutination.

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2
Q

What techniques are used to study virus structure?

A

Electron microscopy, X-ray crystallography, density gradient centrifugation.

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3
Q

How can viruses be detected in a sample?

A

By detecting viral proteins (serological methods) or viral nucleic acids (qPCR, sequencing).

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4
Q

What is a plaque assay used for?

A

To measure virus quantity in PFU/mL by counting plaques formed on a bacterial lawn.

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5
Q

What does LD50 represent?

A

The dose at which 50% of infected organisms die.

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6
Q

What virus model was used in many foundational experiments?

A

Bacteriophages.

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7
Q

What was the significance of the Hershey and Chase (1952) experiment?

A

It demonstrated that DNA, not protein, is the genetic material.

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8
Q

What isotopes were used in the Hershey-Chase experiment?

A

³²P (for DNA) and ³⁵S (for protein).

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9
Q

What did Luria and Delbrück’s fluctuation test prove?

A

That mutations arise spontaneously, not in response to selective pressure.

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10
Q

What is the key concept of the one-step growth curve by Ellis and Delbrück (1939)?

A

Virus replication occurs in stages: infection, replication, assembly, and release.

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11
Q

What is the eclipse period in the one-step growth curve?

A

A phase where no infectious particles are detected as viruses have disassembled and are replicating inside cells.

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12
Q

What defines the rise period in viral replication?

A

Release of mature virions from the host cell.

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13
Q

How is MOI (Multiplicity of Infection) calculated?

A

MOI = (total virus particles) / (total host cells).

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14
Q

Does MOI = 1 mean all cells are infected?

A

No, only ~63% are infected due to the Poisson distribution.

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15
Q

What is the formula for Poisson distribution used in virus infection?

A

P(n) = (mⁿ × e^(–m)) / n!, where m is the MOI.

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16
Q

How do you calculate the percentage of infected cells?

A

P(n > 0) = 1 – P(0).

17
Q

What is burst size?

A

The number of phage particles produced per infected bacterium, calculated as phage yield (PFU/mL) divided by infected bacteria titre (CFU/mL).

18
Q

How can the eclipse period be experimentally measured?

A

By artificially lysing infected cells with chloroform to release intracellular viruses, which are then counted via plaque assay.

19
Q

What happens during the eclipse period?

A

Virus particles disassemble after entering the host, viral genome is released, host DNA is degraded, and viral mRNAs/proteins begin synthesis.

20
Q

What does the intracellular accumulation phase refer to?

A

The period after the eclipse, when new phages are assembled inside the cell but not yet released.

21
Q

When do the curves of total and extracellular virus counts merge in a one-step growth curve?

A

About 40 minutes post-infection, when all cells have lysed.

22
Q

What does burst size measure and how is it calculated?

A

It measures phage particles per infected cell: Burst size = (phage yield in PFU/mL) ÷ (infected bacterial titre in CFU/mL).

23
Q

Why is synchronizing infection important in the one-step growth curve?

A

It ensures that all host cells are infected simultaneously, allowing replication stages to be observed uniformly.

24
Q

In MOI calculation, why can’t you use just the titre of the virus stock?

A

Because MOI depends on the actual number of particles used in the volume added, not just the stock concentration.

25
What is the probability of a cell being uninfected at MOI = 1?
P(0) = e^–1 ≈ 0.37 → 37% remain uninfected.
26
What is the formula for probability that a cell is infected by at least one virus?
P(n > 0) = 1 – P(0).
27
In a culture where MOI = 1, what percentage of cells are infected by 2 phages?
P(2) = (1^2 × e^–1) / 2! = 0.18 → 18%.
28
What’s the Poisson distribution formula for viral infection?
P(n) = (mⁿ × e^(–m)) / n!, where m = MOI.
29
Example: 1x10⁸ phage mixed with 1x10⁸ bacteria. What is MOI?
MOI = 1.
30
Example: At MOI = 1, what percent of cells are infected?
63% → P(n > 0) = 1 – 0.37.
31
Example: Add 100 µL of phage (1×10¹⁰ PFU/mL) to 100 mL culture. Final volume 50 mL. Bacteria = 1×10⁷ CFU/mL. What is MOI?
MOI = 2.
32
For MOI = 2, what is P(n > 0)?
P(0) ≈ 0.14 → P(n > 0) = 0.86 → 86% of cells infected.