lecture 5/6

Question 1

ultracentrifuge

Answer 1

• play vital role in virology
• efficiently sediment even the smallest viruses
• used for concentration and purification of virus

Question 2

rate-zonal centrifugation

Answer 2

-separates viral particles based on mass

Question 3

isopycnic centrifugation

Answer 3

• boyant or equilibrium seperation

- particles separated solely based on buoyant density

Question 4

other forms of virus purification and concentration

Answer 4

-virus purification with membrane chromatography

Question 5

virus quantification

Answer 5

-counts the number of viruses in a specific volume to determine virus concentration

Question 6

virus titer

Answer 6

• lowest concentration of virus that still infects cells

- number of infectious units per ml of sample

Question 7

biological virus quantification tests

Answer 7

• depends on a virus particle initiating a successful replication cycle
• plaque assays
• pock assays
• various endpoint titration methods

Question 8

physical viral quantification tests

Answer 8

• do not depend on any biological activity of the virus particle
• electron microscope particle counts
• hemagglutination
• immunological assays such as ELISA
• quantitative PCR assays
• flow cytometry

Question 9

transmission electron microscopy (direct physical test)

Answer 9

-most direct method to determine the concentration of virus particles in a sample

Question 10

Virus Counter 2100

Answer 10

• physical test

- direct counting

Question 11

Assessment based on antigen concentration (physical test)

Answer 11

• hemagglutination assay

- single radial immunodiffusion (SRID)

Question 12

Assessment based on gene expression

Answer 12

• quantitative polymerase chain reaction

- physical test

Question 13

traditional assays/ biological assays

Answer 13

-plaque (circular zone of necrotic cells surrounded by viable cells in a monolayer)

Question 14

Plaque forming units

Answer 14

• units/mL (PFU)
• measures the number of virus particles capable of forming plaques per unit volume
• ex: if a solution has PFU of 1000 pfu/ml, every ml of solution contains enough virus to form 1000 plaques

Question 15

pock assay (biological assay)

Answer 15

• pock is necrotic area of chorioallantoic membrane of embryonated egg
• unit: pock-forming units/ml

Question 16

transformation assay (biological assay)

Answer 16

• quantitative determination of titers of oncogenic viruses

- unit: focus-forming units/ml

Question 17

quantal assay (biological assays)

Answer 17

-endpoint=virus dilution that affects 50% of test subjects

Question 18

TCID50 (tissue culture infective dose 50)

Answer 18

-tissue culture infectious dose which will infect 50% of the cell monolayers challenged by the defined inoculum

Question 19

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

A. electron microscopy
B. ELISA
C. pock assay
D. qPCR

Answer 19

C. pock assay

Question 20

A PFU/mL of 300 means:

A. 300 viruses are present in 1 ml sample to cause one plaque in monolayer cell culture

B. one virus is present per ml of sample to form 300 plaques in monolayer cell culture

C. the minimum number of viruses present per ml of the sample to form 300 plaques in monolayer cell culture

Answer 20

B.