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Microbiology and Immunology 2500 - Virology > Lecture 2 > Flashcards

Lecture 2 Flashcards

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Biology 101 flashcards
1
Q

What is a virion?

A

A virion is a vehicle used to transport the genome into another host

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2
Q

What host machinery does the virus require?

A

It requires the host’s ribosomes, the host’s transport vesicles, and the host’s energy.

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3
Q

In the viral life cycle, what is “absorption”?

A

Absorption is attachment of the virus to the host cell.

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4
Q

What is the eclipse in a viral life cycle?

A

An eclipse is the time when infectivity disappears. It occurs when the virus is uncoating itself.

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5
Q

What is the latent period of the viral infectious cycle?

A

Occurs with the replication of the genome, when protein synthesis is occurring.

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6
Q

What is maturation in the viral life cycle?

A

Maturation is the assembly of the genome and proteins into the virion.

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7
Q

How long does the viral replication cycle take?

A

Approximately 8-40 hours. Viruses make their bits and pieces (using the host) and then assemble into the infectious virion.

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8
Q

What two characteristics does a host require to be infected by a virus?

A

It must be susceptible and permissive.

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9
Q

What does it mean for a cell to be susceptible to a virus?

A

It means that the host has a functional receptor for the virus to attach to.

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10
Q

What is a susceptible host cell?

A

A cell that has a functional extracellular receptor for the virus.

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11
Q

What is a permissive cell?

A

A cell that has the organelles required for the virus to assemble into a virion.

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12
Q

What is an advantage and a disadvantage of an animal host?

A

Advantage: The best type of host for a virus. Dramatically advanced our understanding of viral knowledge.

Disadvantage: Very costly laboratory model.

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13
Q

What are some advantages of using a fertilized chicken egg as a viral host? What are they typically used for?

A

Fertilized chicken eggs are composed of multiple cell types; the virus can be injected into the yolk sack, the amnion, the embryo, etc. Less costly than animal models.

Perfect host for Influenza A. Chicken eggs are used to grow the influenza vaccine. Each individual egg hosts one single vaccine.

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14
Q

How may cells be used as a host for a virus?

A

Cells can be used by adhering them to a slide, forming a monolayer. Continuous cell lines are formed by injecting the virus into a tumourous cell that is immortal and replicating uncontrollably.

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15
Q

What are cytopathic effects (CPEs)?

A

The different changes that a virus induces in a cell.

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16
Q

What does this photo demonstrate?

A

Demonstrates cytopathic effects. After the cell dies it no longer has the ability to adhere to the slide on the monolayer. Therefore, as time progresses, the virus kills the cells.

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17
Q

What percentage of cancers are caused by human viruses?

A

20%

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18
Q

What are three examples of CPEs?

A
  1. Lysis
  2. Syncytia
  3. Transformation
19
Q

What is syncytia as a CPE?

A

When the plasma membranes of cells fuse together, producing multinucleated cells.

20
Q

What is transformation as a CPE?

A

When cells are no longer flat, but divide uncontrollably to become piles of cells.

21
Q

What is the next step that is to occur if a CPE does not occur?

A

Even if cells fail to show infection, they still need to be proven to be uninfected. Next, measure the infectivity.

22
Q

What is the general idea of a plaque assay in measuring the infectivity of a virus?

A

Adding a virus to cells, and overlaying with a substance (agar). When infected cells release their progeny, the spread is halted by the gel (the agar). The place where the infected cells released their progeny is the plaque.

23
Q

How is a plaque assay conducted?

A

There are 8 test tubes, each with 9 mL of buffer in them. Add 1 mL of concentrated virus to the first test tube (dilution = 10^1). Extract 1 mL of this and add to the next test tube (10^2). Continue until reaching the 8th test tube (10^8). Remove one mL of 10^8 diluted virus and add to a susceptible and permissive host. Cover with agar and allow for plaques to form. Conduct this in 4 petrie dishes, and count and average the number of plaques formed. Multiply this number by the dilution factor 10^8 to calculate the number of plaque forming units/mL.

24
Q

What is the unit of measurement in a plaque assay?

A

PFU/mL

PFU = plaque forming units

25
Q

What is a plaque assay used to measure?

A

The infectivity of a virus.

26
Q

How many clones does a plaque typically represent in a plaque assay?

A

One viral clone. This is due to the high degree of dilution. It indicated that only one viral clone may be required to initiate infection.

27
Q

What is the purpose of using crystal violet staining when conducting a plaque assay?

A

Crystal violet stains the living host cells. Therefore the plaques can be easier to see.

28
Q

What does the particle:PFU ratio measure?

A

The infectivity of a virus. It tells you whether or not all of the virions are infectious or not (ex. you may produce 40 virions but not all of them may be infectious).

29
Q

How is the particle:PFU ratio used? What does it mean if the number obtained is big? Small?

A

Ratio = number of viral particles/number of infectious particles

The smaller the ratio, the more infectious the virus is.

30
Q

What is an example of a virus that forms foci?

A

The Rous Sarcoma Virus (RSV)

31
Q

What is a transformation assay? What are its units? What does it measure?

A

Used for viruses that do not form plaques, but form foci. Measured in foci forming units/mL (FFU/mL). Transformation assays are used to measure the infectivity of a virus.

32
Q

Between a plaque assay and a transformation assay, which is the most effective way to measure viral infectivity?

A

A plaque assay, by far. Much more accurate.

33
Q

What type of viruses always kills the host cell by burst/lysis? When does it occur?

A

Cytopathic viruses. Each host cell has a finite ability to produce virions, and eventually the cell is killed through its lysis.

34
Q

Can a non-cytopathic virus cause cell lysis?

A

No.

35
Q

If a virus is not cytopathic, can infectivity be measured?

A

No, infectivity cannot be measured, physical measures must be used instead.

36
Q

What is the difference between measuring physical viral measures and measuring viral infectivity?

A

Physical: measuring how well the virus can produce virions. Ex. a virus can produce 40 virions.

Infectivity: measuring how infectious the virions produced by a virus are. Measures of infectivity include the entire viral infectious cycle. Ex. virus produces 40 virions, how many of these virions are infectious?

37
Q

What is a hemaglutination assay in terms of physical viral measurement? Why is this considered physical measurement and not a measure of infectivity?

A

A hemaglutination assay involved adding red blood cells to a buffer, along with a virus. If recognition occurs between the red blood cell surface and the virus, a lattice will form (positive). If recognition does not occur, the red blood cells will remain at the bottom in a drop of blood (negative). Keep in mind that with decreasing dilution of the virus, less lattice is formed.

This measures physical infectivity, of the first step of the viral infectious cycle: recognition.

38
Q

How does measuring viral enzyme activity occur? How is to a form of physical measurement?

A

Ex. Measuring the activity of reverse trasncriptase in a retrovirus. When reverse transcriptase is used, add radioactive nucleotides. The host cell cannot convert mRNA to DNA, but retroviruses can. This can proove the presence of radioactive reverse transcriptase, or proove that it is functional.

39
Q

What is immunostaining? How is it a form of physical measurement?

A

Can be direct (one antibody binding to one viral protein) or indirect (an antibody binding to another antibody which binds to the viral protein). The antibody is tagged flourescently. The antibody is then incubated on the monolayer, and the protein of interest can be visualized if the antibody binds.

Allows you to detect the location of specific proteins.

40
Q

What is immunoblotting? How is it a method of physical measurement?

A

Immunoblotting involves taking antibodies and the cell lysate (post-viral infection) and incubating them. It involves running them on a gel and separating by size.

Used to detect the amount of the protein of interest.

41
Q

What is the difference between immunostaining and immunoblotting?

A

Immunostaining: measures the location of the viral protein of interest.

Immunoblotting: measures the amount of the viral protein of interest.

42
Q

What is sequencing as a form of physical measurement? When is it typically used?

A

Typically used for low abundance viral genes. Exponential growth of the gene product, and the revolution of deep sequencing.

Viral gene sequencing is used to detect the presence of a specific mRNA. If transcription is occurring, it is present. If not, absent.

43
Q

How is flourescent tagging used as a form of physical measurement?

A

Take the green fluorescent protein gene and insert it before the viral gene. Virus will transcribe it, and the protein will fluoresce. Can be used to determine which cells have been infected.

44
Q

What are the different measures of infectivity? What are the different physical measures?

A

Infectivity: plaque assay, transformation assay

Physical: immunoblotting, immunostaining, gene sequencing, hemaglutination assay, viral enzyme activity, fluorescent proteins

Microbiology and Immunology 2500 - Virology (12 decks)

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