Virology - reverse transciption etc. Flashcards
what were retro viruses called in the earlier 20th centrury?
tumor viruses
cause they caused tumors
type of genome in baltimore class VI viruses?
have a positive sense, single-stranded RNA genome, but replicate through a DNA intermediate.
what type of viral genome integrates into the host genome?
specifically RNA retro viruses
there are DNA viruses that contain reverse transcriptase in their replication cycle (e.g. hepatitis B) but they don’t integrate
what is RT?
reverse transciptase is an enzyme that has the ability to ‘reverse the flow of genetic info’.
normal flow would be RNA to DNA but in this case, its DNA to RNA to proteins
RT is primer dependent, can be either DNA or RNA primer
the template can also be either one
note: also Bacteria, Archaea, eukaryotes have RT activity in the cells
retro viruses can be broadly divided into?
simple & complex genomes retroviruses
simple like E.g. Avian leucosis virus
complex like HIV
what is unique about the retrovirus genome?
Retroviruses are the only viruses with a diploid genome.
This means that two copies of the viral RNA genome are packaged into the virion.
what is a provirus?
A provirus is an inactive virus genome that is integrated into the DNA of a host cell.
mRNA is the same as?
positive sense RNA
what is a kissing loop complex?
RNA kissing interactions, also called loop-loop pseudoknots, occur when the unpaired nucleotides in one hairpin loop, base pair with the unpaired nucleotides in another hairpin loop.
When the hairpin loops are located on separate RNA molecules, their intermolecular interaction is called a kissing complex.
pbs ?
primer binding site
what is the function of an RNA dimer?
The genome of the retroviruses is a dimer composed by two homologous copies of genomic RNA (gRNA) molecules of positive polarity.
Its believed to contribute to RT viruses resistence to UV light and ionizing radiation.
Another theory is that when mutation occurs in one strand recombination with the other, originally identical, strand would allow the genome to return to nonmutated.
what is “copy-choice” in regard to retroviral replication?
Copy-choice recombination by reverse transcriptases is a mechanism where the new dna molecule comes about by replicating selected parts of each parental dna molecule and by alternating between the two.
two templates could build one functional genome
ppt
polypurine tract
is a primer for plus-strand DNA synthesis during reverse transcription.
LTR
long terminal repeat
is a pair of identical sequences of DNA, several hundred base pairs long, which occur in pseudogenes that form a endogenous retrovirus or a retroviral provirus.
RNase H
an endonuclease enzyme used in retroviral replication
Cleaves RNA only when in duplex form. RNA can be in RNA:RNA or RNA:DNA duplexes.
RNase H
an endonuclease enzyme used in retroviral replication
Cleaves RNA only when in duplex form. RNA can be in RNA:RNA or RNA:DNA duplexes.
what are retroviral elements?
Ancient and modern retroelements in cell genomes (yes, ours too!).
Retroelement is a sequence that moves around in the genome via RT.
ERVs are endogenous viral elements in genomes that closely resemble and can be derived from retroviruses.
They are abundant in the genomes of jawed vertebrates, and they comprise up to 5–8% of the human genome (lower estimates of ~1%).
endogenization
retroviruses infect thegermline (sperm and ova) via endogenization
= endogenous retroviruses (ERVs)
retroelements are typically not infectious (except in mice)
What is unique about hepadnaviruses?
e.g. hepatitis B
are DNA viruses that encode reverse transcriptase.
contain partially gapped double-stranded DNA and replicat via an RNA intermediate.
Sequential assembly
type of virion assembly method
genome is pumped into a preformed empty shell
e.g. Picornaviruses, Herpesviruses
concerted assembly
type of virion assembly method
a protein shell is built around the genome
e.g. influenza virus
what are cellular chaperones in relation to viral assembly?
are cellular proteins that assist in folding reactions
what are the 2 methods of virus assembly called?
sequential and concerted assembly
Budding can be driven by 4 factors:
- viral envelope and capsid proteins can drive budding.
- internal matrix proteins can drive budding.
- envelope proteins can drive budding.
- matrix proteins with additional components needed for efficiency or accuracy.
what are 3 methods of release of new virions from a host cell?
Lysis – host cell bursts
Exocytosis – usees cell’s export pathways
E.g. Coronavirus, Herpesvirus
Budding – buds off from the plasma membrane
E.g. Influenza virus, Retrovirus
Two options for release of of non-enveloped viruses:
lytic and non lytic which are further divided
lytic: apoptotic, viroporins, inhibition of membrane protein synthesis
non lytic: double-membraned vesicles or exosome use
