Feb 24 2014- Viruses

Question 1

What is a virus?

Answer 1

Submicroscopic, infectious, obligate, intracellular parasites

Question 2

What are virions?

Answer 2

Proteins produced with self assembly that can spread themselves to new hosts

Question 3

Advantage of viral dsDNA?

Answer 3

Easily transcribed into mRNA’s by host’s Pol II

[ex. herpes, adenovirus]

Question 4

First step in viral gap-DNA or ssDNA transcription?

Answer 4

Reverse-transcriptase regenerating the gap / making ss into ds
[ex. gap DNA = hep B, ssDNA = parvovirus]

Question 5

Cells have no independent RNA polymerase (to make RNA genome). So all virus genomes have ____.

Answer 5

RDRP, RNA-dependent RNA polymerase

Question 6

Retroviruses contain what kind of viral genome?

Answer 6

(+) ssRNA that are “ribosome-ready” with DNA intermixed

Question 7

What do (-) and (+) ssRNA genome viruses have to do first before they can replicate?

Answer 7

Use RDRP to create the missing (+) or (-) strand; then transcription can begin

Question 8

What do you use a plaque assay for?

Answer 8

To quantify infectivity of a virus

Question 9

What is CPE and what does it indicate?

Answer 9

CPE = CytoPathic Effect ; evidence of viral replication

Question 10

Do all viruses have CPE?

Answer 10

No - bc it’s difficult to culture some viruses on medium

Question 11

Function of capsids?

Answer 11

(helical or icosahedral) They protect the genome and serve as a genome delivery service

Question 12

What is a capsomer?

Answer 12

The surface structures seen in e- micrograph of virus

Question 13

What is a virus envelope?

Answer 13

A host-cell-derived lipid bilayer

Question 14

What are viral spikes?

Answer 14

Virus-derived membrane glycoproteins (w/in the viral envelope)

Question 15

What do Ab’s often recognize on the surface of a virus?

Answer 15

The “spikes” w/in the viral envelope

Question 16

What is the shape of a rabies capsid?

Answer 16

Bullet-shaped; helical capsid

Question 17

What is the shape of an adenovirus capsid?

Answer 17

Complex capsid; many-faced icosahedral

Question 18

What kind of growth curve do viruses have?

Answer 18

Single-step “burst” growth

Question 19

What happens during the latent period in a viral infection?

Answer 19

The virus is replicating inside cells; won’t see it in the host supernatant

Question 20

What allows for close proximity btwn host cell and attaching virus?

Answer 20

Electrostatic binding (then prot-prot interactions take over for actual attachment)

Question 21

How do viruses gain access to many different tissue cell types?

Answer 21

They use one or more receptors, or combo prot-carb receptors

Question 22

What are the co-receptors HIV uses to access a cell?

Answer 22

gp41 and gp120

Question 23

What is the difference in entry for enveloped vs naked viruses?

Answer 23

Enveloped = fusion
Naked = endocytosis (clathrin and caveolin-dependent)

Question 24

Strategies that maintain the compact viral genome?

Answer 24

Alternative splicing, nested RNAs, ambisence coding

IRES elements, leaky scanning for AUG,

Question 25

How are helical capsids created?

Answer 25

They are created contemporaneously with the new viral genome

Question 26

How are icosahedral capsids created?

Answer 26

The capsid is created around the already-made viral genome OR the genome is inserted into a pre-formed capsid

Question 27

What are Negri Bodies?

Answer 27

Cytoplasmic inclusions | Evidence of infection (esp. rabies!)

Question 28

Where do most viruses infect?

Answer 28

At a mucosal membrane (GI, nasal, resp system)

Question 29

What is the incubation period?

Answer 29

The time from viral infection to Sx onset

Question 30

Who is at highest risk for viral infection?

Answer 30

Infants, elderly, pregnant women, immunocompromised

Question 31

Local vs Systemic Infection

Answer 31

``` Local = in and out same pathway (Ap to Ap) Systemic = excreted anywhere (Ap, BL, sides) ```

Question 32

What are the Ab's in a local infection?

Answer 32

Mostly IgM and and IgA

Question 33

Koplik Spots?

Answer 33

White plaque on gums during measles infections

Question 34

What is subacute sclerosing panencephalitis?

Answer 34

Untreated measles that migrated to the brain

Question 35

Talk to me about RSV

Answer 35

Respiratory Synctial Virus | Babies resp. infection that predisposes to perm. lung damage

Question 36

Indirect damage by viral infection?

Answer 36

Taking over the host genome replication mechanisms

Question 37

Direct damage by viral infection?

Answer 37

Membrane damage causing cells to stick together

Question 38

What do you look for when determining CPE?

Answer 38

cell lysis, nuclear shrinking, changes in the membrane, inclusion bodies

Question 39

What is syncytia?

Answer 39

Cell fusion

Question 40

What is pyknosis?

Answer 40

Nuclear shrinking

Question 41

What are some Intracellular Restriction Factors? What do they do?

Answer 41

APOBEC, TRIM5 | They are protective against some classes of viruses

Question 42

What does APOBEC do?

Answer 42

Binds HIV, disallows infection

Question 43

Why does APOBEC not work?

Answer 43

HIV contains the Vif protein, which targets and degrades APOBEC

Question 44

What does TRIM5 do?

Answer 44

Recognizes viral capsids

Question 45

What does INF do?

Answer 45

It is secreted to the neighbors of sick cells and won't allow viral replication in neighbors

Question 46

Type I vs Type II INF? | How are type I/II controlled?

Answer 46

Type I = INFα,β ; ISRE controlled | Type II = INFγ ; GAS-element controlled

Question 47

What does PKR do?

Answer 47

Protein Kinase R decreases viral translation

Question 48

What does OAS do?

Answer 48

Oligoadenylate Synthetase activates the degraders of mRNA

Question 49

Which TLRs are important in viral infection?

Answer 49

TLR 3, 7, 9

Question 50

Humoral vs Innate response?

Answer 50

Humoral is necc for virion recognition | Innate is a cell-mediated response