Basic virology

Question 1

What is a virus?

Answer 1

obligate intracellular parasite that replicate by self-assembly of individual components rather than binary fission

Question 2

Virus genomes can be:

Answer 2

RNA: ss circular or linear ; ds linear
DNA: ss linear, ds circular or linear

Question 3

3 forms of capsids

Answer 3

helical, icosahedral, complex

Question 4

virion for naked virus=

Answer 4

genome+ capsid

Question 5

Some nucleocapsids are surrounded by a lipid envelope that is derived from ____.

Answer 5

cellular membrane

Question 6

Which is more stable; naked or enveloped?

Answer 6

naked

Question 7

How do enveloped viruses spread?

Answer 7

large droplets, secretions, organ transplant, blood transfusions

Question 8

Major steps in viral replication

Answer 8

attachment–> penetration–> uncoating–> early transcription–> genome replication–> late transcription–> assembly–> release

Question 9

What happens in early transcription?

Answer 9

synthesis of nonstructural proteins. DNA viruses use host RNA pol, RNA virus use virally encoded RNA dependent RNA pol

Question 10

What happens in late transcription?

Answer 10

synthesis of structural proteins

Question 11

Where are RNA viruses assembled?

Answer 11

cytoplasm

Question 12

Where are DNA viruses assembled?

Answer 12

nucleus

Question 13

+RNA virus genome replication

Answer 13

translated as polyprotein–> cleaved–> RNA dep polymerase transcribes -RNA as template

Question 14

-RNA genome replication

Answer 14

-RNA virus carries a RNA dependent RNA polymerase–>+RNA

Question 15

The biological assay for infection

Answer 15

plaque assay

Question 16

What is MOI?

Answer 16

ratio of the number of infectious particles to number of target cells. 1 would be 60% of cells, 5-10 ensures all cells are infected

Question 17

Eclipse period

Answer 17

post-penetration phase until virus can be detected intracellularly, ends at virus assembly

Question 18

Latent period

Answer 18

post penetration till cells can be detected extracellularly

Question 19

Complementation

Answer 19

exchange of proteins

Question 20

With complementation, would a mutant be able to replicate in a 2nd cell?

Answer 20

No

Question 21

Recombination

Answer 21

an exchange of genetic material on the same segment of genome

Question 22

Will a mutant virus be able to replicate in a 2nd cell after recombination?

Answer 22

yes

Question 23

Recombination occurs frequently with what type of viruses?

Answer 23

DNA

Question 24

Ressortment

Answer 24

an exchange of genetic material on different segments of genome

Question 25

____ is probably the most common route of infection.

Answer 25

inhalation

Question 26

2 ways of localized spread of viruses

Answer 26

release of virus to surrounded cells, syncytia formation

Question 27

How might a virus spread from the original site of infection?

Answer 27

gain access to lymphatics or blood

Question 28

Incubation period

Answer 28

period postinfection prior to the onset of symptoms

Question 29

Acute phase

Answer 29

symptomatic pase

Question 30

3 forms of persistent infection

Answer 30

chronic, latent, transforming

Question 31

What is a transforming persistent infection?

Answer 31

integrates into cellular DNA or is otherwise maintained in the cell and immortalizes the cell, alters its growth properties

Question 32

What is the first defense against viruses?

Answer 32

IFN and NK cells

Question 33

IFN induced pathways to prevent viral infection

Answer 33

1. PKR ptwy inactivates translation initiation factor eIF-2--> inhibits viral protein translation 2. 2-5A activates RNas L which cleaves RNA 3. Mx ptwy are GTPases that inhibit RNA polymerase activity

Question 34

Role of Ab in viral infection

Answer 34

can neutralize virus binding or facilitate lysis of enveloped viruses with complement

Question 35

Flu like symptoms are caused by ____

Answer 35

IFN and lymphokines

Question 36

Inflammation is caused by ____.

Answer 36

t cells, macrophages, PMNs

Question 37

Hemorrhagic disease is caused by____.

Answer 37

T cells, Ab, complement

Question 38

3 types of antivirals

Answer 38

vaccine, Ig, drugs

Question 39

Which type of viral vaccine gives a strong IgG, IgA, and T cell response that is long lasting?

Answer 39

attenuated

Question 40

Which viral vaccine gives short term immunity that is mostly IgG

Answer 40

killed virus

Question 41

How is immune globulin used for viral vaccination?

Answer 41

pre- and post- exposure prophylaxis

Question 42

What determines the shape of virus capsids?

Answer 42

The shape of capsids is determined by the shape and interaction of capsomeres, which self-assemble.

Question 43

Which type of capsid morphology is best suited for concerted packaging

Answer 43

Helical morphology is best suited for concerted packaging as the self-assembling capsomeres can spiral along with the replicating nucleic acid.

Question 44

Which type of capsid morphology is best suited for sequential?

Answer 44

Icosahedral capsids are best suited for sequential packaging as, typically, a procapsid of partially assembled capsomeres forms and then fully assembles once a unit genome has been inserted into the procapsid.