lecture 6 Flashcards
(33 cards)
under what conditions can viruses be propagated?
obligate intracellular pathogens —> cannot be propagated in cell-free media or dead cells
can propagate in the presence of host cells–> whole animals, eggs, tissues
explain why not all cells will become infected at an moi of 1?
virus associated wit cells at random–> cell infection follows a poisson’s distribution
even when the number of cells equals the number of infectious virions (moi of 1), some cells will be infected by more than one virion
what happens when a single infections forms a plaque?
susceptible cells on Petri dish is overlaid with solution of viral particles
when a infectious particle enters a cell & completes a cycle of replication–> releases baby visions will invade neighboring cells
cycles of virals replication will kill expanding zones of cells–> resulting in plaque OR a region where all cells have died and detached
how is plaque initiated? when will it stop expanding?
do all viruses form plaque?
single infectious particle –> many more visions are generated as the plaque expands, needing more to form it
stops when the surrounding cells go quiescent and are not metallically active
NO
what can virus replication caused on phenotypes?
disease,
lyse cells
cause cytopathic effects (cpe), kill the cells
do not harm
what are plaque assays? how are they visualized?
localized cleaning of a cell lawn by lysis
each plaque imitated by single infectious virus (PFU)
enlarged by that virus’ descendant
-number of cells initially must far exceed the infections virions
at high MOI–> all cells will lyse
what is burst size?
how do cells and virus expand?
number of progeny virions produced by one infected cell
differ
cells: 2^N, N is replication cycles–> log2 scale
viruses: X^N, number of virus replication cycles and X is burst size–> log burst scale, until viable cells are used up
what is CPE?
cytopathic effect –> for some viruses, infection can cause cells to change their appearance because the infection sickens them
- infection can be detected by CPE
what is tissue culture?
The growth of disaggregated primary or transformed cells in liquid medium
what is multiplicity of infection?
number of infectious viral particles that are added per cell in an experiement
what is a receptor?
host encoded molecule on the surface of susceptible cells that is recognized by a particular virus’s visions attachment protein
what is a co receptor?
host encoded molecule on the surface of a susceptible cell that a virus needs ( plus receptor) for cell entry
what is virion attachment protein?
virus encoded protein on the exterior surface of vision that engages in interactions with the virus host cell receptor
depends on virus type–> could be spike or evolope protein
what is RNA dependent RNA polymerase? (RdRp)
virus encoded enzymes that uses RNA as template to generate a complementary RNA strand
what is DNA dependent RNA pol?
pol that uses DNA as template to generate RNA
what is RNA dependent DNA poly (reverse transcriptase or RT)?
use RNA as template to generate complementary DNA
–second strand of DNA is generated by RT, using cDNA as template
- RT can template DNA using RNA or DNA as template
what is segmented genome?
what genome does it constitute?
viral genome that consists of more than one piece of nucleic acid
RNA segments that one virion co encapsidate make one haploid genome
what is subgenomic RNA?
RNA templated by (shorter than) viral genomic RNA
may signify antisense copies of subgeneric RNAS
one way large RNA viruses can generate many mRNA
what are the 7 classes of viral genomes and how each generate mRNA recognizably host genomes?
ss- RNA: copied to + sense that can be translated or templated
ss+ RNA: can be translated directly, but first templates - strand intermediate to template many mRNAs
dsRNA: can be transcribed by viral RNA dep RNA pol
ssDNA: can template second strand and dsDNA can be transcribed
dsDNA: can be transcribed by DNA host depending RNA Pol
retrovirus: RNA copied via Reverse transcriptase to make dsDNA that integrate into host DNA—> are transcribe by host RNA polymerase
gapped dsDNA virus: reverse transcribed viruses–> DNA are transcribed to mRNA and to RNA replication int that are reverse transcribed to generate gapped dsDNA
what information is not contained in viral genomes?
completer protein syntheses machinery
encoding proteins involved in energy production of membrane biosynthesis
what is HIV entrance mechanism?
receptor and coreceptor
usually uses CCR5 coreceptor
evolves when it uses CXCR4 as co receptor
what info is encoded in a viral genome?
replication of viral genome
assembly packaging of the genome
regulation and timing of cycle
modulation of host defenses
spread to other host and cells
what distinguishes between retrovirus and hepadnavirus ?
-encapsided genome of retrovirus are RNA
-they generate & integrate DNA replicated intermediate into infected cells
-Hep B has gapped dsDNA genome
-upon entry, gap is filled & transcribed to —–generate intracellular RNA replication intermediate
-this is Reverse transcribed to generate gapped DsDNA that is incorporated into the progeny irons
what are virus receptors? did they evolve?
what are they?
normal cell molecules that did not evolve for the purpose of benefitting virus replication
–virus evolved to use host molecules that were already where the virus needed to be
–proteins, or carbs (sialicacid–> receptors for influenza)
