L21 RNA replication Flashcards
Possible RNA genome configurations
linear: whole or fragmented
ss: +ve or -ve
ds (rare)
circular ss/ds (extremely rare)
most common configuration
ssRNA
label +ve and -ve strands as coding or non-coding
+ve: coding
-ve: non-coding
what does having a +ve strand mean
proteins can be directly synthesised once in the cell using host ribosome machinery
what must -ve strand do before synthesising proteins
use rdrp to make a +ve strand
where does the rdpd come from
virus
what happens in the first cycle of +ve sense RNA replication
proteins will be directly synthesised from the +ve strand
-one of which is rdrp
what happens in the second cycle of +ve sense RNA replication
the rdrp produced in the first cycle is then used to transcribe genomic RNA or mRNA
why dont -ve strand viruses have to make rdrp
it is already in the capsid
what happens during -ve sense RNA replication
the rdrp from the capsid transcribes the strand into mRNA
the mRNA is translated into proteins
during gene expression what does the genome code for (+ve RNA)
one or two polyproteins
what is a polyprotein
covalently joined smaller proteins
what can a -ve RNA gene encode for
one protein or
two or more proteins
why is the ability to produce multiple proteins from one gene advantages
they have a very small genome so they can make more proteins with less genome
how are polyproteins cleaved
initially by self or host protease
subsequently by viral
example of viruses that form one or two polyproteins from +ve RNA
polio
hep C
SARS-CoV-2
three ways one gene encodes for many proteins
alternative initation
alternative splicing
ribosomal frameshifting (slippage)
what is alternative intiation
using the different methionine start codon down the gene
example of virus that uses gene expression with a segmented genome
influenza
what is alternative splicing
different splice sites are chosen
what is ribosomal frameshifting
the skipping of nucleotides
what is the intermediate of +ve strand RNA replication
-ve strand
what is the intermediate of +ve strand RNA replication
-ve strand
what is the intermediate of -ve strand RNA replication
+ve strand
characteristic of ssRNA replication
5’-3’, like DNA
RNA primer independentant
mostly uses viral components
what happens during dsRNA replication
after entry the rdrp present in the capsid trancirbes the negative strand into multiple +ve strands while still in the capsid
-the +ve strands are then released into the cell to translate viral proteins (rdrp incl.)
example of virus that undergoes dsRNA replication
Rotavirus
what kind of genome does rotavirus have
ds segemented
how retrovirus replicate +ve strand RNA
reverse transcribe to dsDNA in the cytoplasm
dsDNA is transported into the nuclear and integrated into host DNA
example of retrovirus
HIV
what enzyme reverse transcribed the +ve RNA to dsDNA
reverse transcriptdase
what enzyme integrates the double-stranded DNA into the host DNA
integrase
where are integrase and reverse transcriptase packed
viral capsid
what makes reverse transcriptase multifuctional
cna act as
rdrp
dpdp (no proofreading)
ribonuclese H
what does ribonuclease H do
degrade DNA
is reverse transcriptase RNA primer dependant or independent
dependant
how many copies do retroviruses have of the genome in the capsid
two
what do the genomes have on the end
direct repeats
what is the first thing that reverse transcriptdase does
pick up host tRNA that has a similar sequence to the end of the RNA and uses it as a primer to synthesis a DNA version of the end of the DNA
-the DNA then moves on the other end of the second strand and uses it as a template, creating a DNA/ RNA hybrid
