Quiz 6

Question 1

What are the names of two genera within the family Togaviridae?

Answer 1

Alphavirus

Rubivirus

Question 2

What type of proteases carry out the site-specific cleavage of viral polyproteins that occurs in i) P-spaces ii) E-spaces?

Answer 2

P spaces: virus encoded enzymes

E Spaces: host encoded enzymes

Question 3

Which of its co-translationally-cleaved polyprotein fragments encode poliovirus non-structural proteins?

Answer 3

P2, P3

Question 4

What are the primary fates of poliovirus genomic (+)-ssRNA molecules i)at early times after initiation of the infection cycle; and, ii) at late times after initiation of the infection cycle?

Answer 4

Early-genome replication making (-)strand so they can then use the (-) strands to synthesize (+) strands

Late- Replication ends and then proceeds to assembly and maturation of the virion

Gene expression can happen early or late.

Question 5

Briefly describe the events that occur during the initiation of poliovirus RNA synthesis.

Answer 5

P3 binds to 3’ end of viral RNA
3D RNA pol synthesized and attaches first 5’ nucleotide to Vpg
3D polymerase stalls after a few nucleotide bases because it is still tethered to P3

Question 6

What normal, cellular processes are required for toga virus i) penetration, and ii) uncoating?

Answer 6

i) clathrin mediated endocytosis

ii) acidification of the endosome causing conformational changes in the virion

Question 7

What two genetic mechanisms have contributed to the evolution of rubella virus and sindbis virus since their divergence from a common ancestor?

Answer 7

• Mutation

- Recombination

Question 8

From what host species was influenza virus A/Shanghai/2/2013 (H7N9) isolated? is this strain associated with propagated epidemics in humans?

Answer 8

Humans, and no it wasn’t a propagated epidemic since it is H7N9.

Only H1-3 and N1and 2 can be transmitted to humans.

Question 9

Which of the the Sindbis virus replication complexes can synthesize i) both 49s (+)-ssRNA and 26S (+)-ssRNA, and ii) both 49S (+)-ssRNA and 49S (-)-ssRNA

Answer 9

i) nsP1 + nsP2 + nsP3 + nsP4

ii) nsP1 + nsP23 + nsP4

Question 10

What are the two different mechanisms that might be employed by non-enveloped viruses in order to penetrate a eukaryotic host cell?

Answer 10

Direct Injection

Endocytosis

Question 11

From the perspective of the host, what are two positive effects that immune responses can have during a virus-host interaction?

Answer 11

• clearing of the virus

- Resolution of infection

Question 12

What are the two main factors that determine the tissue tropism observed for a given virus?

Answer 12

• prescence of specific protein receptors on the host in the specific organ or tissue
• whether the virus can get into the specific tissue

Question 13

What specific stage of the cellular infection cycle would you expect to be blocked by i) a/b interferons ii) neutralizing antibody?

Answer 13

i) Gene expression

ii) attachment

Question 14

What is the normal generation time of a virus infection that occurs in a dead end host? Explain your reasoning.

Answer 14

There isn’t a generation time of a virus infection of a Dead end host since the pathogen can’t be transmitted. Therefore the generation time is infinite since the host is infected but does not transmit.

Question 15

What two kinds of macromolecule do extracellular virus particles invariably contain?

Answer 15

nucleic acid

proteins

Question 16

What are the two different kinds of virus-encoded proteins that may be involved in genome replication?

Answer 16

• modifier subunits

- Nucleic acid polymerase

Question 17

In the NdNp notation, what is the designation of a reverse transcriptase activity?

Answer 17

RdRp

Question 18

What is a cap structure? On what type of macromolecule would a cap structure be found?

Answer 18

Cap structure is a 7-methyl GTP that is attached 5’ to 5’.

The cap structure is found on a mRNA

Question 19

The double helix is naturally occurring double-stranded nucleic acids is always antiparallel. What is an antiparallel double helix?

Answer 19

double helix strands that run parallel to each other with opposite alignments.

Question 20

By what two mechanisms can genetic variability be introduced into any kind of virus

Answer 20

Mutation

Recombination

Question 21

What are the two fundamental mechanisms by which viral nucleoproteins can be assembled?

Answer 21

Nucleation

Shell stuffing

Question 22

To what taxonomic entity (i.e. order, family, subfamily, genus, or species) does each of the following belong?

(i) Herpesvirales
(ii) Orthomyxoviridae

Answer 22

• order

- family

Question 23

What fundamental characteristic of all DNA polymerases allows some of them to carry out “proofreading” during DNA synthesis?

Answer 23

all DNA polymerases require a primer that helps facilitate the process of proofreading

Question 24

Briefly explain the ‘copy choice’ mechanism that leads to recombination between sRNA viruses

Answer 24

RNA polymerase binds to the 3’ end of the template and synthesizes 5’ to 3’. During RNA synthesis the RNA polymerase may unattached from its template strand and go onto a new strand, carry nascent RNA strand with it. The newly synthesized strand will contain sequences from the original template as well as the new template strand. Depending on the attachment of the RNA polymerase to the new template depends on the newly synthesized strand will be homologous or non homologous.