Hepadnaviridae & Retroviridae Flashcards
What group are hepadnaviridae in?
Group 7–>dsDNA w/ RNA int
True or false: Hepadnaviridae do not need to bring in their own DNA pol
False
-Need to bring in VIRAL RNA dep DNA pol (REVERSE TRANSCRIPTASE)
What pathogens are in Hepadnaviridae
Hepatitis B
Why is Hepatitis B concerning?
-Common–>1/3 of population has gotten it
-90% clear infection, but 1% develop acute liver failure & die
-can develop life long chronic infection (worse in children)
-cirrhosis
-cancer
Differences between Hepatitis A, B, and C
Hep A: Picornaviridae–>Group 4 (+)ssRNA, mild infection, vaccine exists
Hep B: Hepadnaviridae, Group 7 dsDNA w/ RNA int, chronic infection, vaccine exists–>not available globally
Hep C: Flaviviridae, Group 4 (+)ssRNA, chronic, no vaccine
True or false: Hepatitis kills less people than malaria, tuberculosis, and HIV/AIDS
False
-Hepatitis has killed more in 2013
What family is Hepatitis E in?
Togaviridae
Which hepatitis are the biggest killer?
Hepatitis B and C
Is Hepadnaviridae enveloped or non, what type of capsid?
-Enveloped
-Icosahedral
Hepadnaviridae genome characteristics?
-rcDNA (relaxed circular DNA)–>strand is not complete/covalently linked, not circular
-1 DNA strand has viral pol at 5’ end
-Other strand has m7G capped RNA
Hepadnaviridae life cycle
- Entry–> fusion or endocytosis
- Becomes circular dsDNA –>Host DNA pol repairs rcDNA into cccDNA
- RNA transcription (host DNA dep RNA pol)–>5 protein coding mRNA, includes pgRNA
- Protein translation–> 7 proteins
- Encapsidation–>pgRNA is packed into capsids
- Genome synthesis–>made by VIRAL reverse transcriptase
- Budding and exocytosis
Once in the nucleus hepadnaviridae do what?
dsDNA becomes circular by cccDNA (covalently closed circular DNA)
What is an advantage rcDNA becoming cccDNA?
Circular genomes are more stable and can stay for decades
-b/c circular/episomal it is not recognized as non-self by host
How is pgRNA made and what does it do?
HOST RNA makes 5 RNAs that includes pgRNA
-used as a template for reverse transcriptase
True or false: pgRNAs and reverse transcriptase are packaged into virions after reverse transcriptase steps occur
False
-pgRNAs and reverse transcriptase are packaged into virions BEFORE RT steps
Reverse transcription steps for Hepadnaviridae
- RT binds to stem loop at 5’ end to start
- RT switches to identical seq at 3’ end
- DNA is made, RNA is degraded, but a little remains
- The RNA starts 2nd strand synthesis
- 2nd strand uses DNA as template so DNA dep DNA pol is used
- dNTPs are used up and synthesis stops making rcDNA (not circular)
True or false: Hepadnaviridae make many infectious particles
False
-Icosahedral capsid does not need nucleic acid to from so it forms many non-infectious particles
What are satellite virus and example of one
Parasitize the machinery of other viruses
-Hepatitis D
What does Hep D need to be infectious?
Requires co-infection with Hep B virus for envelope proteins
-uses structural proteins of Hep B
Can Hep B exist w/out Hep D?
Yes
-Hep D cannot exist w/out Hep B
What group are Retroviridae in?
Group 6–>(+)ssRNA w/ DNA intermediate
True or false: (+)ssRNA in retroviridae is immediately translated
False
-Immediately reverse transcribed–>converted into dsDNA
Why do Retroviridae turn (+)ssRNA into dsDNA first?
dsDNA is stable
What is packaged in virions in Group 6 and what is packaged in group 7?
Group 6: RNA
Group 7: DNA
Where is reverse transcriptase located in retroviridae?
In capsid
True or false: Retroviridae is non-enveloped
False
-enveloped
-nuclear replication
What pathogens are in Retroviridae?
-Human immunodeficiency virus (HIV)–>does not cause cancer
-Human T lymphotrophic virus (HTLV)–>causes cancer
What 2 states does retroviridae exist in?
- Extracellular RNA retrovirus
- Integrated Provirus
What is provirus?
Genetic info of virus is integrated into genome of host and can replicate
True or false: In retroviridae, once dsDNA integrates it can be excised out
False
-stays forever–>cannot be taken out without killing host
What is in RNA genome in retroviridae
- Repeat region R(U5 and U3)–>genome replication
- Primer binding site (PBS)–>genome replication
- Packaging signal (psi)–>genome packaging
- Viral genes (gag,pol, env)–>polyprotein coding genes
What is in proviral genome in retroviridae
Long terminal repeats (LTR)
-genome replication
Retroviridae life cycle
- Entry: fusion (enveloped)
- Reverse transcription
- Integration (integrase)
Retroviruses need to wait for nuclear envelope of host to break down, what kind if cells can they infect then?
Infect actively replicating cells
Retroviridae reverse transcription steps
- RT primes tRNA at 5’ end
- RT switches to identical seq at 3’ end
- DNA is made, RNA template is degraded, a little remains
- RNA makes 2nd strand synthesis
- 2nd strand uses DNA as template, so RT is DNA dep DNA pol
What is the main difference between Hepadnaviridae and Retroviridae reverse transcription steps
Hepdna: uses stem loop to start
Retro: primes tRNA to start
What is an HIV drug target?
Integrase
How do retroviridae make multiple viral RNAs
Splicing
Where are unspliced RNAs?
Nucleus
What makes structural proteins in retroviridae
Gag
Why is pol produced at low levels?
Retroviruses read through the stop codon 5% of time to make Pol
-Pol doesn’t have its own start codon
What makes non-structural proteins in retroviridae
Pol
What makes envelope proteins in retroviridae
Env
What proteins need to come in with retroviridae?
-Reverse transcriptase
-Host tRNA
-Integrase
-Protease
How does the protease in retroviridae differ frim the protease in Picorna, Flavi, Toga, and Corona?
Protease is only active when virus starts budding off
