Virology Flashcards
what is a virus?
an obligate intracellular parasite that replicates by self assembly of individual components rather than by binary fusion
cannot make energy or proteins indipendent of a host cell
contain a genome of limited size that is either RNA or DNA (not both)
What is a viroid
infectious Nucleic acid
what is a prion?
infectious protein (mad cow)
how can you classify a virus?
1- size
2-morphology (shape adn presance/ absance of envelope)
3-type of genome
4-mechanism of replication
What can virus genomes consist of?
circular or linear ssRNA
linear ds RNA
linear ssDNA
circular or linear dsDNA
what are the types of ssRNA?
+RNA (same as teh sense messager RNA)
-RNA (opp sense of mRNA)
What is a capside?
the packaging protein shell of some viruses; ridgid structures made to withsand the environment
what are the three forms of capsids?
helical
icosahedral or spherical
complex
what is a cucleocapsid composed of?
genome and the capsid
what is a lipid envelope?
a memprane that surrounds the nuceocapsid, and serve as a virus attachment for proteins adn membrane fusion proteins
How stable is the lipid envelope? and why?
not stable!!!!; b/c lipid, so more suseptiable to drying, senstive to detergents and alcohol, and cant survive int eh GI tract
What ways can virsuses penetrate into the host cell?
1) endocytosis
2) membrane fusion,
what are the stages of virus replication?
1) attachement
2) penetration
3) uncoating
4) early transcription
5) genome replication
6) late transcription and sysnthesis of structural proteins
7) assembly of virus particles
8) release of virus particles
What do +RNA function as?
mRNA, and are immediatly translated by cellular ribosomes
How does the +RNA genome get replicated?
the RNA polmerge transcribe a -RNA, and then uses that stand to replicate the complemetary +RNA
What do -RNA function as?
the template for mRNA
Who does the +RNA genome get replicated?
the virsus carries a RNA-dependent RNA polymerase, adn teh resulting +RNA is translated to proteins adn is sued as a template for additional -RNA genomes
What do retroviruses carry?
a RNA-dependent DNA polymerase (reverse transcriptase)
what enzymes produce the retrovirus proteins?
host enzymes
How are DNA viruses replicated?
by host DNA dependent RNA polymerase
How do we measure virus growth in the lab?
1) a hole in the monolyer of cells
2) PFU
3) MOI
what is a lysate?
the suspension of virions in culture medium that results form unrestricted growtyh of virus on a cell monolayer
what is the particle to pfu ratio?
measures the # of cells physical particles compared to the # of infectious virions
what does a plaque assay measure?
the # of infectious virions in a given volumen of lysate, generally plaque forming units (PFU) per ml of lysate= titer
a biological assay of infectivity
what is multiplicty of infection (MOI)
the ratio of # of infectious particles to the to the # of target cells to be infected
a MOI of 1 will be only infecting about 60% of the cells in a monolayer
a MOI b/n 5-10 is needed to ensure that all cells are infected
what are the two periods of a single -cycle growth curve?
eclipse period
latent period
what is the eclipse period?
the post-penetration phase; when there is uncoating, early transcription and genome replication
ends at virus assembly!!!
what is the latent period?
the post-penetration phase until virus can be detected extracellularly
this includes the eclipse phase!!
also includes the assembly and release
why do virual muations occur and how frequently?
high frequency; do to the large # of genome copies produced in every infected cell, due to polymerase errors esp for RNA viruses
what can virus genome undergo?
complementation
recombination
reassortment
what is complementation?
an exchange of proteins, occurs when cell is infected by two viruses with differnt genomes, and a lethal mutation in gene X arises, the normal WT gene can compensate for the mutant gene
what is recombination, what type of viruses does it occur in? (RNA or DNA, or BOTH)
an exchange of genetic material on teh same segment of genome; if a genome with a lethal mutation in gene X arises along with the WT genome in teh same cell, then teh mutation can be removed by recombination with a WT gene for X;
occurs frequently for DNA viruses, does not occur in RNA viruses
What is reassortment?
an exchange of genetic material on differnt segments of genome; if two segmented viruses infect the same cell they can exchange some of their segments at the same time of virus assembly; resulting in a novel strain of virus that is composed of segments from both of the parents
what is important in the mechanism of generation of new influenza strains?
reassortment!!!!
what are the routes of entry/ transmission?
1) fecal-oral route
2) respiratory
3) blood-bone
4) sexual transmission
5) maternal-neonatal
6) animal reservoir or arthropod vector
how can viruses enter?
1-breaks in the skin
2-inhalation (prob most common)
3-initial replication is in cells that express receptors for the virus, and contain app. cellular factors for replication
4-localized spread
what are the ways for localized spread?
1) release of virus from an infected and subsequent infection of sourrounding cells
2) some enveloped viurses can fuse on infected cell with uninfected cells to directly spread to surrounding cells
what is syncytia formation?
some enveloped viurses can fuse on infected cell with uninfected cells to directly spread to surrounding cells
What are ways of secondary spread?
1) may spread from primary site by gaining accessing the blood stream
2) can gain access to the CNS by circumventing the blood-brain barriers trhough the CSF or dircet uptake in peripheral nerves
What is viremia?
the persance of virons int he blood
what is the incubation period? are patinets contagious during this period?
the period post infection prior to onset of symptoms, yes pts are infectious during this without knowing
if requrie secondary spread how long is the incubaiton period?
12-14days
What is HIV’s incubation period?
extended incubation of mo to yrs.
What is acute phase of infection?
is the sympomatic phase of the infection, most viral infections resolve following this phase
what kind of patients are seen to have persistent infections?
immunocompromised pts.
what are the three froms of persistent infections?
1) chronic (productive)
2) latent
3) transforming
what is a chronic persistent infection?
when the virus is produced at low levels but may not continue to cause disease sympoms
what is latent persistant infections?
virus genome remains int he cell indefinaitely, but virus particles are not produced, except during reactivation (herpes)
waht is a transforming persistant infection?
intact or partial virus genome integrates into cellular DNA or its otherwise maintained in the cell and immortalized the cell, alters its growth properties (oncogenic viruses)
What are the first defense responders in a virus infection?
NK cells, and INF, PRRs (Toll-like receptors)
main PAMPs-dsRNA, and others are unmethylated DNA adn 5’ modified ssRNA
then INFs bind to suroudnig uninfected cells to induce pathways that pervent virus replication
Who does INF prevent viral replication?
1- the protein kinaze (PKR) pathways inactivates translation factor eIF-2, inhibits viral protein translation
2– 2-5A systems activates Rnase L which clease RNA, destorying RNA genomes or hinhibiting viral transcription
3-Mx pathway preoteins are GTPases that inhibit RNA polymerase activity
-the Ds RNA activates the first and second pathwya
what are the antigen-specific responses (cellular and humoral)?
1) CD8+ are teh major cellular response to priamry viral infections; infected cells are trageted for lysis through antigen presentation
2) antibodies can neutralizee viruses binding or facilitate the lysis of enveloped viruses with complement
what are the immune defecnse that viruses have evolved to contain?
1) antigen variation to excape the hormal response
2) inhibition of antigen presentation to escape cellular response
3) cytokine homologes that v regulate or block cellular resonse
4) latent infection in neurons where there is not MHC class I
What are the three theypes of antivirals?
1) vaccines
2) immunoglobulin
3) drugs
what are the 3 basic types of vaccines?
live attenuated
killed virus
subunit (recombinant DNA)
