Virus Quantitation and replication Flashcards
Virus titration
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
virus titer
the number of infectious units per ml
quantitative assays
measure the exact number of infectious virus particles in the sample
monolayer plaque assay
used to determine titers only of viruses that cause visible cell damage
viral plaques
colorless areas of necrotic cells surrounded by viable cells stained with a vital dye
plaque-forming unit
the technique can be used both for accurate quantitative assay of virus infectivity and for purification of virus particles
Pock assay
involves the titration of certain viruses, eg, poxviruses and herpesviruses on the chorioallantoic membrane of the chick embryo
oncogenic viruses
transform cells, so that they display reduced contact inhibition
contact inhibition
a phenomenon in which cells stop dividing when their cell membranes make contact
quantal assay
this method does not measure the exact number of infectious particles in the inoculum, rather, it determines only the presence or absence of infection
permissive cell
a cell that contains the necessary intracellular components need for virus replication
nonpermissive cell
a cell type that does not allow a complete virus replication cycle
multiplicity of infection
the number of infectious viruses inoculated per cell
extracellular virons
viruses free in the maintenance medium
eclipse period
refers to the time between the “ disappearance of infectious virions and the appearance of the first progeny virons intracellularly
latent period
during this period, extracellular virions cannot be detected
receptor-mediated endocytosis
this process involves the selective binding of ligands to specific cell membrane receptors
clathrin
a latticework of fibrillar protein that coats the cytoplasmic face of coated pits
uncoating
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
the key events in viral replication are:
- protein synthesis
- replication of the viral genome
- assembly of the new components into virons
viral proteins:
- ensure replication of viral genome
- package the geneome into virons
- alter the structure/ function of the infected cell
provirus DNA
serves as a template for transcription of viral mRNA by a cellular transcriptase
transcription
the process by which information contained in a nucleic acid molecule is transferred to messenger RNA
capping
stabilizes the mRNA and aids in aligning mRNA on the ribosomes during translation
Poly (A) tail
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
introns
noncoding sequences
exons
noncontiguous coding sequences
monocistronic mRNA
mRNA that encodes one polypeptide
polycistronic mRNa
mRNA that encodes several polypeptides
semiconservative replication
process of DNA replication in which the two parental strands separate, each serving as a template for the synthesis of new progeny strands
helicase
promotes unwinding of the DNA double helix
single-stranded DNA- binding proteins
helix-destabilizing proteins that keep the two separate DNA strands apart until each has been copied
DNA polmerase
used to copy each strand from the origin of replication in a 5’ to 3’ direction
Okazaki fragments
short fragments synthesized as intermediates in the discontinuous replication of DNA and later joined to form and intact strand
extracellular spread (type 1)
virons are released from the cell to spread in the extracellular milieu
intracellular spread (type 2)
virions spread from cell to cell through desmosomes of intracellular bridges (cell fusion) without contact with extracellular milieu
nuclear spread ( type 3)
the viral genome is latent or integrated into the host genome and is passed from parent to progeny during cell division
