Virus Replication

Question 1

T/F: viruses prefer to use host cell machinery to produce new virions, but when host cells aren’t available, viruses can still multiply by division.

Answer 1

FALSE!! Viruses do not have the capability of replicating without using host cell machinery!

Question 2

In a _______ cell, a virus is able to replicate, but in a _________ cell, one or more factors necessary for viral production are missing or do not allow replication.

Answer 2

permissive; non permissive

Question 3

What is MOI (multiplicity of infection)?

Answer 3

Number of virions that a cell is expected to take in per infection.

Question 4

What period of viral replication starts just after uncoating and lasts until right before the appearance of the first new extracellular viral particle?

Answer 4

Latent period

Question 5

What period of virus replication starts after uncoating and lasts until just before the appearance of the first new intracellular virus particle?

Answer 5

Eclipse period

Question 6

Are extracellular virions detected during the latent phase?

Answer 6

No, it ends just before the new virion leaves the cell

Question 7

What is the burst size?

Answer 7

Number of infectious virions released on average per cell

Question 8

What are the steps of virus replication?

Answer 8

Attachment
Penetration
Uncoating
Syn of viral components
Assembly and maturation
Release

Question 9

T/F: virus attachment to receptors on host cells is very specific

Answer 9

TRUE!

Question 10

T/F: if a cell lacks the specific receptor the virus needs to bind, the cell is safe from attack.

Answer 10

TRUE!

Question 11

T/F: In all cases, as long as the host cell receptor is correct, a virus can attach and enter the cell.

Answer 11

FALSE - sometimes a co-receptor is needed for entry

Question 12

T/F: Some viruses can be compatible with more than one host cell receptor.

Answer 12

TRUE - ie. HIV

Question 13

2 ways naked viruses can penetrate the cell

Answer 13

Receptor/Clathrin mediated endocytosis (common)

Pore mediated penetration/injection (sometimes)

Question 14

2 ways enveloped viruses can penetrate the cell

Answer 14

Surface membrane fusion (pH independent fusion protein)

Receptor mediated endocytosis (pH dependent fusion protein)

Question 15

What method do a few viruses, like FIP, use to enter the host cell?

Answer 15

Antibody mediated attachment and penetration

Question 16

Surface membrane fusion of enveloped viruses can induce what immune response?

Answer 16

Antibody dependent cell mediated cytotoxicity. (Virus leaves membrane with Ag on the host cell membrane, Ab attach and signal NK cells to kill the host cell)

Question 17

When enveloped viruses use receptor mediated endocytosis to enter a cell, how does the pH dependent fusion protein work?

Answer 17

Virus enters cell within a vesicle, which is then passed into an endosome where the pH drops. Low pH allows the fusion protein to fuse the viral envelope with the endosomal membrane and release its capsid into the cell.

Question 18

During the uncoating phase, can the virus be detected in the body?

Answer 18

No, it is inside the cell and basically an undercover spy.

Question 19

Uncoating leads to loss of viral _______.

Answer 19

Infectivity

Question 20

What enzyme converts viral RNA into cDNA during replication?

Answer 20

Reverse transcriptase

Question 21

In order for the host cell translation system to recognize the viral mRNA, Processing of Primary RNA Transcript/Pre-RNA must occur, which includes the following modifications:

Answer 21

1. Capping (addition of 5’ methylated cap)
2. Addition of Poly-A tail to 3’ end
3. Splicing (removal of introns, joining of exons)

Question 22

After the processing modifications, where does translation of the mRNA take place within the cell?

Answer 22

Cytoplasm

Question 23

Where can assembly and maturation of the new virions take place within the cell?

Answer 23

Nucleus
Cytoplasm
Cell membrane (most enveloped viruses)

Question 24

What type of viruses are able to release progeny from the cell by budding?

Answer 24

Enveloped viruses only!

naked viruses don’t have a membrane to fuse with the host cell membrane

Question 25

How do naked viruses release progeny from the host cell?

Answer 25

Lysis

Question 26

When can certain viruses exit the cell via exocytosis?

Answer 26

When they obtain an envelope while budding from the Golgi or ER membrane. Vesicles migrate to plasma membrane and exit via exocytosis.

Question 27

During the replication of retroviruses, after the viral RNA is translated into DNA by reverse transcriptase, what enzyme inserts the viral DNA into the host genome?

Answer 27

integrase

Question 28

3 types of cell-to-cell spread of viruses

Answer 28

1. Extracellular
2. Intercellular (cell-to-cell without contacting the ECF - remain undetectable)
3. Nuclear (viral DNA incorporated into host cell DNA and passed to progeny during replication)