Virus Quantification + Virus Replication

Question 1

Define virus quantification

Answer 1

Counts the # of viruses in a specific volume to determine virus concentration

Question 2

What is a virus titer measuring?

Answer 2

lowest conc. of virus that still infects cells

or infectious units per ml of sample

Question 3

What is a biological quantification test dependent on?

Answer 3

the virus particle initiating successful replication cycle

Question 4

What is a physical quantification test dependent on?

Answer 4

• does NOT depend on any biological activity of the virus particle

Question 5

What are examples of biological quantification tests?

Answer 5

1. Plaque assay
2. Pock assay
3. Various end point titration methods

Question 6

What are examples of physical quantification tests?

Answer 6

1. Electron microscopy
2. Hemagglutination
3. Immuno assays (ELISA)
4. qPCR
5. Flow cytometry

Question 6

What is the most direct method to determine the concentration of virus particles in a sample?

Answer 6

Transmission Electron Microscopy (TEM)

** PHYSICAL TEST

Question 6

Give examples of a physical test that directly counts viral particles in solution

Answer 6

1. TEM
2. Virus counter 2100

Question 7

What physical tests are an assessment based on antigen concentration?

Answer 7

1. Hemagglutination assay
2. Single radial Immunodiffusion (SRID)

Question 8

What is a plaque?

Answer 8

circular zone of necrotic cells surrounded by viable cells in a monolayer

Question 8

What physical tests are an assessment based on gene expression?

Answer 8

qPCR

Question 8

Which biological test measures the number of virus particles capable of forming plaques per unit volume?

Answer 8

Monolayer plaque assay

Question 8

If a solution has a PFU of 500 pfu/mL, what does this mean?

Answer 8

every mL of solution contains enough virus to form 500 plaques

Question 9

What is a pock?

Answer 9

Necrotic area on chorioallantoic membrane (CAM) of embronated egg

Question 10

Pock assay is a biological or physical test?

Answer 10

Biological

Question 11

Which biological test is a quantitative determination of oncogenic viruses?

Answer 11

Transformation assay

Question 12

What are the units used in a transformation assay?

Answer 12

Focus-forming units / mL

Question 13

What is the endpoint of a quantal assay?

Answer 13

Virus dilution that affects 50% of test subjects

Question 14

What is TCID50?

Answer 14

tissue culture infectious dose which will infect 50% of the cell monolayers

Question 15

Which of the following is not a physical assay for quantification of viruses?

A. ELISA
B. Electron microscopy
C. Pock assay
D. qPCR

Answer 15

C. Pock assay - biological

Question 16

What is a permissive cell?

Answer 16

A cell that allows a virus to replicate

cell machinary that supports replication

Question 17

What is a non permissive cell?

Answer 17

A cell that lacks necessary factors for viral replication

Ex: lack of appropriate receptors

Question 18

What is MOI?

Answer 18

Multiplicity of Infection

Refers to # of virions added per cell during infection

Question 19

What is the latent period?

Answer 19

After uncoating and until just before 1st appearance of EXTRACELLULAR new virus particle

**no extracellular virions are detected at this stage

Question 20

What is eclipse period?

Answer 20

After uncoating and until just before 1st appearance of INTRACELLULAR new virus particle

Question 21

What is burst size?

Answer 21

of infectious virions released per avg cell

Question 22

What are the steps of virus replication?

Answer 22

1. Attachment 2. Penetration 3. Uncoating 4. Synthesis of viral components 5. Assembly + maturation 6. Release in large numbers

Question 23

True or False: Each virus has its own specific receptor(s) on specific host cells

Answer 23

TRUE - lock and key!

Question 24

What virus uses more that 1 host cell receptor for attachment?

Answer 24

HIV

Question 25

What is a co-receptor?

Answer 25

An additional surface molecule on host cells that is required for entry of viruses

Question 26

How do non-enveloped/naked viruses penetrate and the host cell?

Answer 26

1. Receptor mediated endocytosis (most common) 2. Pore mediated penetration

Question 27

How do enveloped viruses penetrate and uncoat in the host cell?

Answer 27

** depends on type of fusion protein 1. Surface membrane fusion -pH independent fusion protein 2. Receptor mediated endocytosis - pH dependent fusion protein

Question 28

What are other uncommon methods of entry for viruses?

Answer 28

Ab mediated attachment and penetration ** seen in FIP virus

Question 29

What viruses inject their genome into the host cytoplasm through creation of a pore in the host membrane?

Answer 29

Non enveloped viruses **pore mediated penetration

Question 30

How does FIP virus infect the host cell?

Answer 30

Antibody mediated attachment and penetration -enters host macrophage by attaching spike proteins to CD13 receptor on host cell

Question 31

At which phase in viral replication can virions no longer be detected?

Answer 31

Viral uncoating

Question 32

What are the functions of the parent virus?

Answer 32

1. Multiple copies for new viruses 2. Viral proteins for capsid and successful replication

Question 33

What does reverse transcriptase do?

Answer 33

Converts viral RNA to cDNA during viral replication

Question 34

How does processing of primary RNA transcript (pre-RNA) occur?

Answer 34

1. Capping- adding 7-methylguanosine to 5' end 2. Adding poly-A tail to 3' end 3. Splicing

Question 35

What is capping?

Answer 35

Addition of 7-methylguanosine to the 5' end of RNA

Question 36

What is RNA splicing?

Answer 36

process that REMOVES INTRONS and JOINS EXONS

Question 37

_____ are the portion of a gene that codes for AA

Answer 37

exons

Question 38

________ are the portion of the gene that does not code for AA

Answer 38

Introns

Question 39

What is constitutive splicing?

Answer 39

all introns are spliced out, all exons are spliced in

Question 40

What is alternative splicing?

Answer 40

All introns spliced out, only selected exons are spliced in

Question 41

Where does assembly and maturation of the virus occur?

Answer 41

1. Nucleus 2. Cytoplasm 3. Plasma/cell membrane (most enveloped viruses)

Question 41

What types of viral mRNA are there?

Answer 41

1. Monocistronic - mRNA that encodes 1 polypeptide 2. Polycistronic - mRNA that encodes many polypeptides

Question 42

Where does assembly and maturation take place in most enveloped viruses?

Answer 42

Plasma membrane / cell membrane

Question 43

How do naked viruses release progeny of new virions?

Answer 43

1. Lysis of host cell

Question 44

How do enveloped viruses release progeny of new virions?

Answer 44

Budding + exocytosis

Question 45

________ viruses can not exit the host cell by budding

Answer 45

Naked viruses bc no envelope

Question 46

___________ integrates viral DNA into the host genome

Answer 46

Integrase

Question 47

How do viruses spread from cell to cell?

Answer 47

1. Extracellular spread 2. Intercellular spread 3. Nuclear spread of virus genome

Question 48

________ results in rapid virus dissemination, evasion of immune system, and persistent infections

Answer 48

Intercellular spread of viral genome