Virology Quiz 2 Retroviruses

Front 1

are retroviruses enveloped? What characterizes their genome?

Back 1

yes; they have two identical copies of +ssRNA

Front 2

which 3 genes are encoded by all nondefective retroviruses?

Back 2

gag, pol, and env

Front 3

what does the pol gene of retroviruses encode?

Back 3

reverse transcriptase and integrase

Front 4

what are the two subfamilies of medically important retroviruses? Which are responsible with AIDS formation?

Back 4

oncoviruses and lentiviruses; lentiviruses

Front 5

what are the two phases in a retroviral life cycle?

Back 5

extracellular phase as a viral particle and intracellular phase as a provirus

Front 6

what is a provirus?

Back 6

a double-stranded DNA copy of the retrviral genome integrated into host cell chromosome

Front 7

what impact do inhibitors that block DNA synthesis have on retroviruses?

Back 7

they are blocked

Front 8

what is the nature of reverse transcriptase?

Back 8

RNA-directed DNA polymerase

Front 9

what are the long terminal repeats of retroviral genomes? What is their role?

Back 9

5' and 3' ends of the RNA genome that get repeated during reverse transciption; they contain regulatory elements for viral transcription

Front 10

where is reverse transcriptase located in the viral particle?

Back 10

bound to the nucleocapsid

Front 11

where does RT begin the conversion of ssRNA to dsDNA in retroviruses?

Back 11

at a primer of cellular tRNA

Front 12

what is the initial product of RT? How is the viral RNA destroyed?

Back 12

DNA-RNA hybrid; RNAse H, a part of the RT enzyme

Front 13

which viral protein in retroviruses catalyzes the integration of the dsDNA into the host genome?

Back 13

integrase

Front 14

what are the 2 fates of RNA transcripts from retroviral genes?

Back 14

they are spliced, exported and transported AND they are packaged into nucleocapsids

Front 15

how do retroviral particles exit the host cell?

Back 15

by budding through the plasma membrane

Front 16

what are the two broad categories of oncogenic retroviruses? Which have an oncogene?

Back 16

acute transforming viruses and nonacute transforming viruses; acute transforming viruses

Front 17

why are acute transforming retroviruses normally defective?

Back 17

the oncogene replaces one of the normal genes

Front 18

what are the four classifications of oncogenic retroviruses based on their appearance under the electron microscope?

Back 18

A, B, C, D

Front 19

which species is infected by Rous sarcoma virus? What is the name of the oncogene in this virus?

Back 19

chickens; src

Front 20

is the oncogene in Rous sarcoma virus required for the induction or maintenance of the transformed phenotype?

Back 20

both

Front 21

is there an src homolog in normal cell cultures? What is the term used to describe this gene?

Back 21

yes; proto-oncogene

Front 22

what does the oncogene src from rous sarcoma viruses encode?

Back 22

a tyrosine kinase

Front 23

which kinase is more active, the normal Src protein in healthy tissues or the oncogenic protein?

Back 23

oncogenic protein

Front 24

what are the 5 categories of molecules known to be products of proto-oncogenes?

Back 24

growth factors, growth factor receptors, protein kinases, signal transducing G proteins, and nuclear proteins that regulate transcription and DNA replication

Front 25

what is the problem with defective retroviruses?

Back 25

they cannot produce infectious virions unless the cell is also infected with a related nondefective retrovirus, called a helper virus

Front 26

what is unique about the isolates of a cell infected with a defective virus?

Back 26

they contain both the defective and helper virus

Front 27

why is the viral oncogene transcribed at such high levels in infected cells?

Back 27

because the retroviral promoter is very active to make viral mRNA for replication and translation

Front 28

do nonacute transforming retroviruses have an oncogene? Are they defective?

Back 28

no; no

Front 29

how long does it take a nonacute transforming retrovirus to cause cancer in the host?

Back 29

months or years

Front 30

how does a nonacute transforming retrovirus become oncogenic? What is the name for this?

Back 30

it places the host cell's proto-oncogene under control of the retroviral promoter; insertional activation

Front 31

what are the names of the only oncogenic human retroviruses? What type of cancer do they cause?

Back 31

human T-cell leukemia virus-1 and 2; T cell leukemia (HTLV1)

Front 32

where is human T-cell leukemia endemic?

Back 32

southern Japan, central Africa, Caribbean

Front 33

how are HTLVs transmitted?

Back 33

horizontally via sexual contact or in blood.

Front 34

what are the symptoms of someone infected with HTLV? What percentage of people develop adult T-cell leukemia eventually?

Back 34

normally asymptomatic; 0.1%

Front 35

what is viral tax protein and what is its role in HTLV infections?

Back 35

it is a transcription factor that induces IL-2 and it's receptor; it may set up an autocrine loop and predispose a cell to transformation]

Front 36

what is the leading cause of cancer deaths worldwide?

Back 36

primary hepatocellular carcinoma from Hep B

Front 37

what percentage of HBV infected individuals become chronic carriers of HBV and express the virus for life? What percentage of carriers go to to develop primary hepatocellular carcinoma?

Back 37

5%; 2-4%

Front 38

do tumors in primary hepatocellular carcinoma have integration of viral DNA?

Back 38

yes

Front 39

what is theorized to predispose a hep B patient for primary hepatocellular carcinoma?

Back 39

destruction of liver by immune response then regeneration, which may lead to mutations

Front 40

how is hepadnaviral replication similar to retroviral replication?

Back 40

utilizes reverse transcriptase

Front 41

what is unique about the hepadna genome?

Back 41

it has two gapped ss regions

Front 42

what type of polymerase is encoded by the hepadnaviral genome? What is the role of this enzyme in hepadna infection?

Back 42

reverse transcriptase; fills in gaps in genome

Front 43

what is the term used to describe the long RNA copies of the entire genome made by RNA polymerase in hepadna infections?

Back 43

pregenomes

Front 44

what is the next step following the transcription of pregenome in hepadna infections?

Back 44

nucleocapsid forms around RNA pregenome and they are copied into DNA by reverse trancriptase INSIDE THE NUCLEOCAPSID

Front 45

what is the big difference between the action of reverse transcriptase in retroviral and hepadnaviral infections?

Back 45

with retroviruses, reverse transcription takes place early in infection; with hepadnaviruses, reverse transcription takes place late in infection

Front 46

what is the name of the drug that can inhibit the reverse transcriptase of both retroviruses and hepadnaviruses?

Back 46

lamuvidine

Front 47

what percentage of HCV patients develop life-threatening cirrhosis?

Back 47

20%

Front 48

does the HCV viral genome integrate into host genome?

Back 48

no

Front 49

what is a high risk factor for carcinogenesis in HBV and HCV infections?

Back 49

alcoholism