Deck 28: Retroviruses

Question 1

Which of the following describes the first step in the replication cycle of retroviruses?

A)Replication of the host genome into daughter DNA molecules.
B)Integration of the viral genome into the host cell DNA.
C)Translation of the viral genome into protein.
D)Transcription of the viral genome into mRNA.
E)Reverse transcription of the viral genome into dsDNA.

Answer 1

E

Question 2

Which of the following describes the phenomenon of promoter occlusion seen in retroviruses?

A)Transcription from the left-hand LTR inhibits transcription from the right-hand LTR.
B)Cellular RNA polymerase can only recognize the factors bound to the left-hand LTR.
C)The inability of the LTR to be transcribed because it has integrated into heterochromatin in the host cell genome.
D)Deletion of the left-hand LTR inhibits transcription from the right-hand LTR.
E)Transcription from both LTRs can occur simultaneously.

Answer 2

A

Question 3

Important discoveries about retroviruses were responsible for Nobel Prizes awarded to all of the following scientists EXCEPT:

A)Robert Gallo
B)Peyton Rous
C)Howard Temin
D)David Baltimore
E)Michael Bishop

Answer 3

A

Question 4

Which of the following is a description of the long terminal repeats found in retroviruses?

A)They consist of direct repeats found at the ends of the incoming viral genome.
B)They consist of direct repeats found at the ends of the provirus.
C)They consist of inverted repeats found at the ends of the incoming viral genome.
D)They consist of inverted repeats found at the ends of the provirus.
E)They are the repeats found in the host cell genome on either side of the integrated viral provirus.

Question 5

All of the following are distinct features of the reverse transcription process,used by retroviruses to convert their ssRNA genome into a dsDNA provirus,EXCEPT…

A)A significant number of cellular enzymes are required to carry out reverse transcription.
B)The viral reverse transcriptase uses a cellular tRNA molecule as a primer.
C)The R sequence present at both ends of the viral genome is critical in the reverse transcription process.
D)There are two separate strand transfer events where the nascent DNA strand is moved to the other end of the template.
E)Degradation of segments of the viral RNA,when bound to a complementary strand of DNA,is important for the process.

Question 6

The Gag and Pol proteins are coded for in two different reading frames in the avian retroviruses.Which of the following mechanisms is used to produce the Pol proteins?

A)Alternative mRNA splicing.
B)RNA editing.
C)Read through of a translational stop codon.
D)Ribosomal frameshifting.
E)Initiation of translation at a downstream start codon.

Question 7

Which of the following statements about the integration of the retrovirus provirus into the host genome is FALSE?

A)The viral integrase makes a staggered cut in the host cell DNA at the site of integration.
B)During integration,two bases are lost from each end of the viral provirus.
C)Integration results in a 4-6bp direct repeat of the host cell DNA on either side of the provirus.
D)Retroviruses produce an enzyme that can remove the provirus from the cellular genome.
E)Cellular host DNA repair enzymes are involved in the integration process.

Question 8

Which of the following primarily determines the species and type of cell infected by a specific retrovirus?

A)The tRNAs found in the cytoplasm.
B)The host cell receptor found on the cell.
C)The types of transcription factors in the nucleus.
D)The level of deoxynucleotide triphosphates in the cytoplasm of the cell.
E)All of the above.

Question 9

Most retroviruses cause cancers in their animal hosts.

Question 10

Which of the following determines the level of viral mRNAs produced from the integrated provirus in retrovirus infected cells?

A)The level of mRNA splicing and polyadenylation that occurs.
B)The amount of reverse transcriptase packaged into the virion.
C)The site in the host cell genome where the provirus integrates.
D)Binding of specific transcription factors to the U5 region.
E)Binding of specific transcription factors to the U3 region.

Question 11

Nontransforming retroviruses can cause an infected cell to become tumorigenic by doing which of the following?

A)The virus inactivates the cellular pRb protein.
B)Integrating into and disrupting a cellular oncogene.
C)Inducing the host cell to enter S phase and begin DNA replication.
D)Integrating into and disrupting a tumor suppressor gene.
E)Integrating the LTR adjacent to a proto-oncogene.

Question 12

Most retroviruses,with the exception of lentiviruses,can only infect cells that are actively dividing.Which of the following explains the primary reason for this?

A)The viral genome is amplified by replicating cells.
B)They need actively replicating cells to spread the virus throughout the body.
C)They need the cell to undergo mitosis so the viral genome can enter the nucleus.
D)They need the cell to produce high levels of nucleotide triphosphates.
E)They need the cell to produce DNA polymerase to replicate the viral genome.

Question 13

Which of the following statements about acute transforming retroviruses is TRUE?

A)They produce viral enzymes that lead to cellular transformation.
B)They cause tumors because of where they integrate into the host genome.
C)They carry a mutated or deleted version of a cellular gene.
D)They are usually competent to replicate and produce virions.
E)They only transform cells in which the provirus has not been integrated.

Question 14

The viruses in the gammaretrovirus genus use which of the following mechanisms to synthesize the proteins from the pol gene?

A)Alternative mRNA splicing.
B)RNA editing.
C)Read through of a translational stop codon.
D)Ribosomal frameshifting.
E)Initiation of translation at a downstream start codon.

Question 15

Retroviruses package a positive ssRNA genome,which resembles an mRNA and is immediately translated upon entry into the host cell.

Question 16

Which of the following ensures that the Pol protein is packaged into the virions of retroviruses during assembly?

A)The Pol protein is bound to a fatty acid.
B)The Pol protein is packaged as a Gag-Pol fusion protein.
C)The Pol protein binds to the packaging sequence on the viral genome.
D)The Pol protein is translated into the lumen of the endoplasmic reticulum.
E)The Pol protein binds to the reverse transciptase enzyme during assembly.

Question 17

All of the following features are associated with the incoming RNA genomes of retroviruses EXCEPT:

A)5' cap structures
B)3' poly(A)tails
C)Repeated (R)sequence at each end of the genome.
D)A single open reading frame.
E)Unique sequences at each end of the genome.

Question 18

The reverse transcriptase enzyme of retroviruses includes between 1 and 10 mistakes when it copies the viral genome into DNA.Which of the following explains why?

A)It lacks the 3'-to-5' exonuclease activity found in the cellular DNA polymerase.
B)It lacks the 5'-to-3' exonuclease activity found in the cellular DNA polymerase.
C)It doesn't bind to the cellular proteins involved in proofreading.
D)The virus doesn't produce the proteins involved in proofreading.
E)The production of RNA is inherently more mistake prone than the production of DNA.

Question 19

What is the enzymatic function of the RNaseH activity of reverse transcriptase?

A)It converts RNA sequence to DNA sequence.
B)It converts RNA sequence to RNA sequence.
C)It degrades single-stranded RNA.
D)It degrades RNA in an RNA:DNA hybrid.
E)It degrades RNA in an RNA:RNA hybrid.

Question 20

Retroviruses use which of the following cellular molecules as the primer for genome replication?

A)The TATA-box binding protein.
B)The 5S ribosomal RNA.
C)A specific transfer RNA.
D)A spliceosome snRNA.
E)A specific spliceosome protein.

Question 21

When retroviruses integrate their provirus into germ line cells they can be vertically transmitted.

Question 22

The envelope protein is translated from the unspliced mRNAs produced during retrovirus infections.

Question 23

Explain the different mechanisms used by acute transforming viruses and nontransforming retroviruses to cause tumor formation.Why does transforming by the acute transforming viruses take less time than the nontransforming retroviruses?

Question 24

The double-stranded proviral genome of retroviruses is longer than the incoming single-stranded RNA genome.What is the function of this extra DNA sequence and where did it come from?

Question 25

Retroviruses only integrate into a few very sequence specific sites within the host cell genome.

Question 26

Unlike most other viruses,retroviruses package two identical copies of their genome in the virion.