viral genome replication and expression L15 Flashcards
(21 cards)
viral genomes can be …..
dsDNA
ssDNA
ssRNA
dsRNA
circular
linear
non-segmented
segmented
what is the importance of segmented or non segmented genomes in viruses
segmented genome - divided in separate segments, each segment encodes different proteins to undergo reassortment - different viruses mix if they infect same cell to allow for rapid evolution
non-segmented is one continuous molecule, genetic variation only occur with mutation only
polymerases
all RNA viruses encode RNA-dependent RNA polymerases
what happened when a +Ve strand RNA enters a cell?
+ve RNA strands are the same sense (same as) mRNA so they can be immediately translated by host ribosomes - really fast !!!
and the first thing that is made is the viral RNA -dependent RNA polymerase to then copy the viral RNA genome
what must -ve strand RNA virus carry inside the virion?
-ve RNA strand is complementary to mRNA, anti-sense so cannot be directly translated, so the virus needs to carry its own RNA polymerase to convert the -ve to +ve RNA after entering before transcription/translation can occur - slower
protein synthesis of DNA viruses
same flow of information as cell - DNA —> RNA —> Proteins
- makes use of cell transcription and translation machinery
protein synthesis of RNA viruses
need to overcome issues, as do not have an RNA dependent RNA polymerase in eukaryotic cells and do not usually encode for more than one protein on each mRNA
overcome this by encoding their own RNA-dependent RNA polymerase
poly protein production - how do RNA viruses get around the ‘one protein per mRNA’ issue
- poly protein production - produce one long protein and then clean into individual proteins via viral or host proteases - seen in poliovirus
subgenomic RNA production - how do RNA viruses get around the ‘one protein per mRNA’ issue
- subgenomic RNA production - make shorter subgenomic RNA that each encode different proteins, made by viral polymerase - seen in coronavirus
segmented genome -how do RNA viruses get around the ‘one protein per mRNA’ issue
genome is split into mutliple RNA segments where each one encodes a different protein
seen in influenza
internal ribosome entry site (IRES) - how do RNA viruses get around the ‘one protein per mRNA’ issue
ribosomes can bind internally to mRNA rather just at the 5’ caps, allowing multiple proteins to be translated, different start points
leaky scanning, ribosomal frameshift and stop codon read through - how do RNA viruses get around the ‘one protein per mRNA’ issue
trick ribosomes into starting at different start codons or shift reading frames to allow for production of multiple proteins from overlapping coding sequence
seen - HIV
anti-viral drugs
targeting a unique aspect of viral replication
- attachment antagonists
- inhibiting uncoating
- inhibiting DNA/RNA synthesis
- Blocking maturation
ATTACHMENT ANTAGONISTS
they block virus from binding to receptors on host cell surface, if no attachment, no entry
maraviroc blocks CCR5 receptor to prevent HIV from attaching
inhibiting uncoating
these stop virus from releasing its genetic material inside host cell, without the uncoating, viral replication cannot begin
inhibiting DNA/RNA synthesis
these target viral polymerases to prevent virus from copying its genome
Blocking maturation
these interfere with viral protein processing and so new viral particles are non-infectious and often target viral proteases
what is viral shedding
shedding is the release of viral particles from the host
happening in saliva, mucus, blood etc and this is how viruses spread to other hosts
what is the advantage of having an envelop virus?
can evade the immune system easier as can fuse to host membranes and has lipid membrane from host- little bit more protect
however, most fragile in environment
what is advantage of not having an envelop?
makes the virus harder, survives longer outside host and is often spread via fecal-oal route
