7+13 Virology 1&2

Question 1

What is variolation, and what was its historical significance?

Answer 1

Purposeful inoculation of a healthy person with a virus by introducing smallpox pustule material to an abrasion. This was the earliest form of vaccination.

Question 2

What disease did the first vaccination protect against?

Answer 2

Smallpox

Question 3

What two criteria for life are viruses missing?

Answer 3

Metabolic activity and the ability to respond on demand

Question 4

T or F: Viruses can grow on non-living medium.

Answer 4

False– viruses NEED cells to grow

Question 5

What is the function of the viral capsid?

Answer 5

Protects the viral genome and binds to the host cell

Question 6

What is the function of the viral envelope?

Answer 6

Protect the nucleocapsid and binds the host cell

Question 7

Define ‘nucleocapsid’.

Answer 7

A viral genome wrapped in a protein coat.

Question 8

What is a capsid made of?

Answer 8

Protein

Question 9

What is an envelope made out of?

Answer 9

Host cell derived structures (phospholipid, glycoprotein, and protein)

Question 10

_______ (encapsidated / enveloped) viruses are more hearty in the environment.

Answer 10

Encapsidated (enveloped viruses are essentially covered in cell membrane)

Question 11

How do encapsidated viruses exit the host cell?

Answer 11

Lysis

Question 12

How do enveloped viruses exit the host cell?

Answer 12

Lysis or budding

Question 13

Encapsidated viruses do best in ______ (wet/dry) environments.

Answer 13

Dry

Question 14

Enveloped viruses do best in ______ (wet/dry) environments.

Answer 14

Wet

Question 15

How do encapsidated viruses spread?

Answer 15

Fecal, oral, fomite, dust

Question 16

How do enveloped viruses spread?

Answer 16

Systemic or mucosal

Question 17

What structural components to enveloped viruses contain that encapsidated viruses do not?

Answer 17

Phospholipids and glycoproteins

Question 18

What kind of cells are encapsidated viruses best adapted to?

Answer 18

Cells with cell walls

Question 19

What kind of cells are enveloped viruses best adapted to?

Answer 19

Cells without cell walls

Question 20

T or F: Viruses can contain both DNA and RNA.

Answer 20

False (viruses can have one or the other, not both)

Question 21

(Positive sense / antisense) RNA can be translated directly into protein by the host cell.

Answer 21

Positive sense

Question 22

Describe (in broad terms) how retroviruses make mRNA.

Answer 22

The viral genome encodes a reverse transcriptase, which turns positive sense RNA into DNA. The mRNA is made from the DNA.

Question 23

If viruses share similar antigenic properties, what does that tell you about their genetic relatedness?

Answer 23

Viruses with similar antigenicity tend to be closely related because the genome encodes the antigenic properties.

Question 24

If a virus is easily transferred by fomites, then it is most likely _____ (encapsidated/enveloped).

Answer 24

Encapsidated

Question 25

What does a virus do during the latent period?

Answer 25

Makes enzymes to regulate the replication process, copies of the viral genome, and proteins to form the coating. Late in the latent period the virus will be assembling into new viruses.

Question 26

From entering to exiting the host cell, what are the steps associated with viral replication?

Answer 26

Attachment
Entry
Uncoating (if enveloped)
Replication
Protein synthesis
Assembly
Release

Question 27

What is the general MOA of antiviral drugs?

Answer 27

Disruption of specific steps in the viral replication cycle

Question 28

Describe how nucleoside analogs work as antiviral drugs.

Answer 28

They are activated by viral enzymes and mimic free nucleosides in the host cell cytosol. When they are added to viral mRNA during transcription, they act as chain terminators so no more nucleosides can be added.

Question 29

What is the primary difference between DNA viral replication and RNA viral replication?

Answer 29

DNA viruses replicate in the nucleus, RNA viruses (usually) replicate in the cytoplasm

Question 30

T or F: Specific viruses will only be able to use specific attachment and entry receptors.

Answer 30

F – many viruses can use multiple receptors

Question 31

How is trophism of viruses determined?

Answer 31

Attachment and entry receptors on the host cell

Question 32

Describe the three general ways that a virus can enter a host cell and what kind of virus (enveloped/non-enveloped) uses each method.

Answer 32

Direct penetration - non-enveloped. The virus bind an attachment receptor and the genome is inserted through the plasma membrane.

Membrane fusion - enveloped. Glycoproteins on the viral surface bind attachment receptors and trigger binding of the envelope and the cell membrane.

Endocytosis - enveloped or non-enveloped. Binding to the attachment receptor causes the cell to engulf the virus. The virus is then trapped inside a vesicle and must have a way to get out to replicate.

Question 33

(Positive/antisense) RNA viruses need to bring their own polymerase to the host cell. Why?

Answer 33

Antisense, because it is not recognized by the host cell as mRNA.

Question 34

How are structural (spike) proteins added to enveloped vs. encapsidated viruses?

Answer 34

In enveloped viruses, the spike proteins are made in the ER, processed in the Golgi, transported to plasma membrane in vesicles, and embedded into plasma membrane. Viral nucleocapsid then buds off of the plasma membrane w/ spike proteins.

In encapsidated viruses, the spike proteins encapsulate the viral genome in the cytoplasm and the new viruses are released upon cell lysis (NO BUDDING).

Question 35

How do enveloped viruses get into respiratory, genital, or intestinal secretions from polar cells?

Answer 35

Budding off the apical side of epithelial cells

Question 36

How do enveloped viruses spread systemically from polar cells?

Answer 36

Budding off the basal side of polar cells

Question 37

Why are electron micrographs useful in identifying viruses?

Answer 37

Because viruses tend to have distinct physical characteristics that can be observed

Question 38

Describe how a hemeagglutination assay works.

Answer 38

Matrix (solvent and sample) are added to test wells along with RBCs (usually from duck or goose). If a virus that causes hemagglutination is present, the viruses will agglutinate and the matrix will remain light red. If the RBCs are not agglutinated, they will sink down to the bottom of the well and form a dark red dot.

Question 39

Describe how a hemagglutination inhibition assay works.

Answer 39

Virus, antibody, and RBCs are added to the test well matrix. If there is virus specific to the antibody, it will form an antibody-antigen complex and no agglutination will occur. If there is no antibody for the virus present, the virus will cause hemeagglutination.

Question 40

Describe how an ELISA assay works.

Answer 40

In a plate, an antibody specific to a virus is added and will stick to any viruses present. A wash solution is used to remove any excess antibody not complexed with the virus. A second antibody with a fluorescent indicator is added which will bind to the first antibody-virus complex.

Question 41

Describe how qPCR works.

Answer 41

YOU MUST ALREADY KNOW THE COMPLETE VIRAL GENOME
A probe that is complementary to the viral genome is added downstream to a primer where transcription will occur. The probe contains a fluorophore and a quencher which blocks the fluorescence. When the polymerase begins translate and form DNA, the polymerase will have higher affinity for the DNA than the probe, so the probe will break off and the quencher and fluorophore will separate, allowing for fluorescence.

Question 42

Why is it useful to observe cytopathic effects of a virus in cell culture, and what’s something you should keep in mind when doing this?

Answer 42

Because viruses have morphologically distinct ways of killing host cells. Remember that this only tells you that something in the culture has cytopathic effects (bacteria or other things can also kill cells)

Question 43

Describe how a plaque assay works.

Answer 43

Serial solutions of a patient sample are inoculated onto a culture plate, with another layer of overlying agar. Any virus that buds off will only be able to inoculate the cells right next to it, making ‘holes’ (plaques) in the solid cell interface.