Feb 24 2014- Viruses Flashcards
What is a virus?
Submicroscopic, infectious, obligate, intracellular parasites
What are virions?
Proteins produced with self assembly that can spread themselves to new hosts
Advantage of viral dsDNA?
Easily transcribed into mRNA’s by host’s Pol II
[ex. herpes, adenovirus]
First step in viral gap-DNA or ssDNA transcription?
Reverse-transcriptase regenerating the gap / making ss into ds
[ex. gap DNA = hep B, ssDNA = parvovirus]
Cells have no independent RNA polymerase (to make RNA genome). So all virus genomes have ____.
RDRP, RNA-dependent RNA polymerase
Retroviruses contain what kind of viral genome?
(+) ssRNA that are “ribosome-ready” with DNA intermixed
What do (-) and (+) ssRNA genome viruses have to do first before they can replicate?
Use RDRP to create the missing (+) or (-) strand; then transcription can begin
What do you use a plaque assay for?
To quantify infectivity of a virus
What is CPE and what does it indicate?
CPE = CytoPathic Effect ; evidence of viral replication
Do all viruses have CPE?
No - bc it’s difficult to culture some viruses on medium
Function of capsids?
(helical or icosahedral) They protect the genome and serve as a genome delivery service
What is a capsomer?
The surface structures seen in e- micrograph of virus
What is a virus envelope?
A host-cell-derived lipid bilayer
What are viral spikes?
Virus-derived membrane glycoproteins (w/in the viral envelope)
What do Ab’s often recognize on the surface of a virus?
The “spikes” w/in the viral envelope
What is the shape of a rabies capsid?
Bullet-shaped; helical capsid
What is the shape of an adenovirus capsid?
Complex capsid; many-faced icosahedral
What kind of growth curve do viruses have?
Single-step “burst” growth
What happens during the latent period in a viral infection?
The virus is replicating inside cells; won’t see it in the host supernatant
What allows for close proximity btwn host cell and attaching virus?
Electrostatic binding (then prot-prot interactions take over for actual attachment)
How do viruses gain access to many different tissue cell types?
They use one or more receptors, or combo prot-carb receptors
What are the co-receptors HIV uses to access a cell?
gp41 and gp120
What is the difference in entry for enveloped vs naked viruses?
Enveloped = fusion Naked = endocytosis (clathrin and caveolin-dependent)
Strategies that maintain the compact viral genome?
Alternative splicing, nested RNAs, ambisence coding
IRES elements, leaky scanning for AUG,
How are helical capsids created?
They are created contemporaneously with the new viral genome
How are icosahedral capsids created?
The capsid is created around the already-made viral genome OR the genome is inserted into a pre-formed capsid
What are Negri Bodies?
Cytoplasmic inclusions
Evidence of infection (esp. rabies!)
Where do most viruses infect?
At a mucosal membrane (GI, nasal, resp system)
What is the incubation period?
The time from viral infection to Sx onset
Who is at highest risk for viral infection?
Infants, elderly, pregnant women, immunocompromised
Local vs Systemic Infection
Local = in and out same pathway (Ap to Ap) Systemic = excreted anywhere (Ap, BL, sides)
What are the Ab’s in a local infection?
Mostly IgM and and IgA
Koplik Spots?
White plaque on gums during measles infections
What is subacute sclerosing panencephalitis?
Untreated measles that migrated to the brain
Talk to me about RSV
Respiratory Synctial Virus
Babies resp. infection that predisposes to perm. lung damage
Indirect damage by viral infection?
Taking over the host genome replication mechanisms
Direct damage by viral infection?
Membrane damage causing cells to stick together
What do you look for when determining CPE?
cell lysis, nuclear shrinking, changes in the membrane, inclusion bodies
What is syncytia?
Cell fusion
What is pyknosis?
Nuclear shrinking
What are some Intracellular Restriction Factors? What do they do?
APOBEC, TRIM5
They are protective against some classes of viruses
What does APOBEC do?
Binds HIV, disallows infection
Why does APOBEC not work?
HIV contains the Vif protein, which targets and degrades APOBEC
What does TRIM5 do?
Recognizes viral capsids
What does INF do?
It is secreted to the neighbors of sick cells and won’t allow viral replication in neighbors
Type I vs Type II INF?
How are type I/II controlled?
Type I = INFα,β ; ISRE controlled
Type II = INFγ ; GAS-element controlled
What does PKR do?
Protein Kinase R decreases viral translation
What does OAS do?
Oligoadenylate Synthetase activates the degraders of mRNA
Which TLRs are important in viral infection?
TLR 3, 7, 9
Humoral vs Innate response?
Humoral is necc for virion recognition
Innate is a cell-mediated response
