Virus Quantitation and replication

Question 1

Virus titration

Answer 1

is a quantitative determination of viral activity , ie, the concentration of virus in the sample which can produce disease, lesions, or some recognizable effect in the host

Question 2

virus titer

Answer 2

the number of infectious units per ml

Question 3

quantitative assays

Answer 3

measure the exact number of infectious virus particles in the sample

Question 4

monolayer plaque assay

Answer 4

used to determine titers only of viruses that cause visible cell damage

Question 5

viral plaques

Answer 5

colorless areas of necrotic cells surrounded by viable cells stained with a vital dye

Question 6

plaque-forming unit

Answer 6

the technique can be used both for accurate quantitative assay of virus infectivity and for purification of virus particles

Question 7

Pock assay

Answer 7

involves the titration of certain viruses, eg, poxviruses and herpesviruses on the chorioallantoic membrane of the chick embryo

Question 8

oncogenic viruses

Answer 8

transform cells, so that they display reduced contact inhibition

Question 9

contact inhibition

Answer 9

a phenomenon in which cells stop dividing when their cell membranes make contact

Question 10

quantal assay

Answer 10

this method does not measure the exact number of infectious particles in the inoculum, rather, it determines only the presence or absence of infection

Question 11

permissive cell

Answer 11

a cell that contains the necessary intracellular components need for virus replication

Question 12

nonpermissive cell

Answer 12

a cell type that does not allow a complete virus replication cycle

Question 13

multiplicity of infection

Answer 13

the number of infectious viruses inoculated per cell

Question 14

extracellular virons

Answer 14

viruses free in the maintenance medium

Question 15

eclipse period

Answer 15

refers to the time between the “ disappearance of infectious virions and the appearance of the first progeny virons intracellularly

Question 16

latent period

Answer 16

during this period, extracellular virions cannot be detected

Question 17

receptor-mediated endocytosis

Answer 17

this process involves the selective binding of ligands to specific cell membrane receptors

Question 18

clathrin

Answer 18

a latticework of fibrillar protein that coats the cytoplasmic face of coated pits

Question 19

uncoating

Answer 19

this is the physical separation of the viral nucleic acid from the envelope and/or capsid such that the viral genome can express its function

Question 20

the key events in viral replication are:

Answer 20

1. protein synthesis
2. replication of the viral genome
3. assembly of the new components into virons

Question 21

viral proteins:

Answer 21

1. ensure replication of viral genome
2. package the geneome into virons
3. alter the structure/ function of the infected cell

Question 22

provirus DNA

Answer 22

serves as a template for transcription of viral mRNA by a cellular transcriptase

Question 23

transcription

Answer 23

the process by which information contained in a nucleic acid molecule is transferred to messenger RNA

Question 24

capping

Answer 24

stabilizes the mRNA and aids in aligning mRNA on the ribosomes during translation

Question 25

Poly (A) tail

Answer 25

acts as a signal allowing mRNA to be transported out of the nucleus and also aids in the binding of mRNA t host cell ribosomes

Question 26

introns

Answer 26

noncoding sequences

Question 27

exons

Answer 27

noncontiguous coding sequences

Question 28

monocistronic mRNA

Answer 28

mRNA that encodes one polypeptide

Question 29

polycistronic mRNa

Answer 29

mRNA that encodes several polypeptides

Question 30

semiconservative replication

Answer 30

process of DNA replication in which the two parental strands separate, each serving as a template for the synthesis of new progeny strands

Question 31

helicase

Answer 31

promotes unwinding of the DNA double helix

Question 32

single-stranded DNA- binding proteins

Answer 32

helix-destabilizing proteins that keep the two separate DNA strands apart until each has been copied

Question 33

DNA polmerase

Answer 33

used to copy each strand from the origin of replication in a 5’ to 3’ direction

Question 34

Okazaki fragments

Answer 34

short fragments synthesized as intermediates in the discontinuous replication of DNA and later joined to form and intact strand

Question 35

extracellular spread (type 1)

Answer 35

virons are released from the cell to spread in the extracellular milieu

Question 36

intracellular spread (type 2)

Answer 36

virions spread from cell to cell through desmosomes of intracellular bridges (cell fusion) without contact with extracellular milieu

Question 37

nuclear spread ( type 3)

Answer 37

the viral genome is latent or integrated into the host genome and is passed from parent to progeny during cell division