Concepts in Virology

Question 1

virus

Answer 1

invasive biological agent that reproduces inside the cells of living hosts

Question 2

virion

Answer 2

extracellular infections virus particle

Question 3

enveloped v non enveloped

Answer 3

non- nucleic acid + protein coat

enveloped- nucleic acid + lipid membane

Question 4

what about virus replication distinguishes them from other small microorganisms?

Answer 4

they do not replicate by fision. but by a synthesis of components

Question 5

eclipse period

Answer 5

an absence of any detectable virion following infection

Question 6

how many types of nucleic acid does a given virus contain

Answer 6

viruses may contain either DNA or RNA, either single stranded or double stranded, but a given virus will have only one variant

Question 7

outline the replication cycle of a virus

Answer 7

adsorption
penetration
uncoating
synthesis of virus parts
assembly of new virions
maturation
release

Question 8

what do cells provide that viruses need?

Answer 8

1. machinery for translations of viral mRNA into viral proteins
   2 energy (ATP)
   3 low molecular weight precursors
   4 enzymes and factors required during the life cycle
   5 cellular transport pathways/machinery

Question 9

what does the virus bring with it

Answer 9

1 genes for virion proteins
2 genes for proteins that are not in the virion
3 genes for replication proteins (may or may not end up in the virion)

Question 10

describe “susceptible and permissive”

Answer 10

susceptible- cell must express a host cell receptor that permits binding and entry

permissive- the virus must be able to overcome cellular defenses and contain the necessary resources to permit viral reproduction

Question 11

all viruses make mRNA that can be translated by host ribosomes

Answer 11

ok

Question 12

list some challenges of being a virus

Answer 12

1. must encounter hosts and host cells
   2 must evade or bypass physical defenses of host (skin, mucous layers
   3 once inside the host, must avoid defense and find cells susceptible and permissive for their reproduction

Question 13

do viruses contain a lot or a little genetic information?

Answer 13

a little

Question 14

describe the common nucleocapsid

Answer 14

most viruses are nucleic acids within a symmetrical protein coat.

the coat is made of identical building blocks, capsomers, arranged in a icosahedral (20 sided, 12 verticies; could also be helical). this structure is incredibly stable

Question 15

what are complex viruses

Answer 15

enveloped viruses- have a lipoprotein membrane surrounding the nucleocapsid

Question 16

describe viral neutralization

Answer 16

neutralization is the process of Ab binding to a viral antigen

all viral antigens are proteins

naked viruses- the capsomers are the Ags
enveloped- the proteins on the lipid membrane are the Ag

Question 17

growing viral cell cultures

Answer 17

relatively slow process that usually confirms the presence of a virus but not its identity

Question 18

cytopathic effect

Answer 18

virus infected cells change in appearance- size, shape, motility, attachment, or continued existence.

this can usually be seen under microscopy

Question 19

lytic viruses

Answer 19

rapidly kill host cells when virions are released

Question 20

tumor/transforming viruses

Answer 20

do not cause death or obvious cytopathic effects. however, cultured cells will show abnormal proliferation rather than death

Question 21

inclusion bodies

Answer 21

in tissue culture, infected cells can be stained to reveal the suspected identity of a virus.

the inclusion bodies generally represent sites where viral replication or assembly is occuring. their presence and location may be indicative of a specific virus

Question 22

plaques and PFUs

Answer 22

plaques are zones of cell death caused by cytopathic effects.

plaque forming units- the only measure of infectious virions in a clinical sample

Question 23

syncytia

Answer 23

cells fuse together to form multinucleated cells

Question 24

list some methods of detecting the reactions of virions and a specific Ab

Answer 24

1.  neutralization- only works on infectious virions; irreversible binding by an Ab identifies and neutralizes a virus
2 complement fixation
3 hemagglutination
4 flourescent Ab
5 ELISA

Question 25

describe 2 “slow” Ab tests to diagnose a viral disease

Answer 25

1. use known antisera against each potential virus (given presentation), apply it to isolated virus
   2 compare pre-immune response and post-immune response samples from a pt. the post-sera will show signficant Ab change against one of potential known viruses

Question 26

seroconversion

Answer 26

2 samples taken- pre and post immune response. a seroconversion is when the post has Ab where the pre did not

seropositive- Ab against a given virus is present
seronegative- Ab against a given virus is not present

Question 27

window period

Answer 27

when Ab production lags several weeks initial infection and is not serologically detectable

Question 28

what are 2 “quick” viral diagnosis techniques

Answer 28

1. viral protein antigens detected using fluorescent Ab

2 PCR

Question 29

Ab production is useful for preventing what parts of the viral lifecycle

Answer 29

adsorption and penetration. Ab neutralizes viruses by irreversibly binding to them.

this does not require lattice formation b/c viruses generally have repeating protein subunits and thus both sites on the Abs can bind

Abs have no effect on intracellular multiplication

Question 30

passive immunization

Answer 30

circulating Abs that can prevent/reduce disease. Abs did not come from the host

Question 31

IgA is important for which viruses

Answer 31

viruses that infect the respiratory tract and GI tract

Question 32

simple RNA nucelocapsids have what shape protein coat and where do they replicate?

Answer 32

icosahedral, cytoplasm

Question 33

simple DNA nucelocapsids have what shape protein coat and where do they replicate?

Answer 33

icosahedral, nucleus

Question 34

describe the stability of simple nucelocaspids

Answer 34

incredibly stable and thus routes of transmission do not require direct contact

Question 35

adsorption determines what two properties?

Answer 35

host range- which animals are susceptible

tissue tropism- which tissues can be infected

Question 36

treatment of polio with phenol results in what?

Answer 36

phenol removes the protein coat, leaving only naked RNA. however the RNA will still infect a host if taken up by a non specific mechanism

Question 37

describe the mechanisms used by Polio virus

Answer 37

polio is a plus-sense RNA virus, meaning it can serve directly as mRNA. an RNA dependent- RNA polymerase is needed for this transcription, and it is made in the cytosol. it uses cellular ribosomes to translate mRNA

polio viral RNA is very disruptive to the host cell. it forms 8 functional proteins, including capsomer proteins and RNA dependent- RNA polymerase.

Question 38

plus and minus stranded RNA

Answer 38

plus stranded- can serve as mRNA

minus stranded- complementary to mRNA

Question 39

baltimore classification scheme

Answer 39

groups viruses into families depending on their type of genome and their method of replication

Question 40

viremia

Answer 40

infections virions in the blood

Question 41

incubation period

Answer 41

length of time between infection and onset of symptoms

Question 42

3 patterns of infection

Answer 42

1 virus growth in site of entry causes no illness, but produces viremia that allows for infection of other tissues. long incubation period and effective vaccine lasts life

2 virus growth does cause illness at site of infection. short incubation period. immunity depends on IgA and only lasts temorarily.

3. virus growth in site of entry does not cause illness, virus spreads via neural pathways. long incubation period

Question 43

acute v persistent infections

Answer 43

acute- infection cleared

persistent- infection not cleared