Old Quiz 4 questions

Question 1

What two steps of the poliovirus infection cycle specifically are facilitated by its reprogramming of host cells?

Answer 1

Gene expression

Genome replication

Question 2

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 2

early - making the minus sense strand or replication
feed into replication

later - not going into new replication complexes.
go into virus particles for assembly and maturation

gene expression early and late

Question 3

What are the routes of horizontal transmission utilized by (i) poliovirus; (ii) rubella virus?

Answer 3

i) polio - fecal oral

ii) rubella- respiratory aerosol (droplet)

Question 4

In the cellular infection cycle of poliovirus, what occurs during the maturation stage?

Answer 4

The VPO (Vp4 and Vp2) is cleaved/seperated inside the virion to activate the virion.

Question 5

What two transmission routes can be utilized by rubella virus?

Answer 5

• respiratory aerosol (droplet)

- placental-fetal

Question 6

What are the reservoirs of (i) alphaviruses, and (ii) rubella virus?

Answer 6

i) non-human animal reservoirs and insect reservoirs with incidental transmission to humans
ii) only human reservoir

Question 7

Where do ribosomes bind to the viral genomic RNA during infection by a picornavirus?

Answer 7

Ribosomes bypass the 5’ end and bind directly to the ribosome landing pad (RLP)

Question 8

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

Answer 8

Alphavirus

Rubivirus

Question 9

What are two ways in which picornaviruses hijack (or reprogram) their host cells? (hint: think about gene expression and about genome replication).

Answer 9

1. gene expression -. Cap binding protein inactivated by viral proteases. Blinding the ribosomes to viral genome. Translation of most mRNAs is blocked off.
2. genome replication - vesicles fusion to cis-Golgi inhibited. Back up a “lake” of vesicles to add the replicase complexes. Creates more membrane area for replication to occur.

Question 10

What is the biochemical basis for the asymmetric accumulation of (+)- and (-)- strands that is observed for most kinds of ssRNA viruses?

Answer 10

• change the RNA sequence for the minus strand to allow for greater binding affinity. This will allow for greater copying thereby producing more +.

Question 11

During what stage(s) of the picornavirus infection cycle does the VPg play a role?

Answer 11

-Genome Replication (used as primer)

Question 12

Which products of poliovirus polyprotein processing are generated by co-translational cleavage?

Answer 12

• P1 and P2

Question 13

What type of site-specific proteases are active in (i) E-spaces, and (ii) P- spaces?

Answer 13

P spaces= viral encoded enzymes

E spaces= host encoded enzymes

Question 14

Where in the host cell does poliovirus genome replication take place?

Answer 14

-cytoplasm

Question 15

What occurs during the transition between the initiation and elongation phases of poliovirus RNA synthesis?

Answer 15

-the 3D polymerase stalls and can’t move any further along template while still attached to P3, so 3C protease must cleave P3 into individual proteins so 3D CAN RESUME nucleotide addition to the new strand of RNA

Question 16

Initiation of poliovirus RNA synthesis

Answer 16

• P3 binds to 3’ end of viral RNA template
• 3D RNA pol copies template and joins first 5’ nucleotide to vpg
• 3D pol stalls and can’t move further while still tethered to P3