9/ viral genetics 2 Flashcards
(12 cards)
1
Q
what are lysogenic viruses able to do
A
- integrate into the host rather than escape from it
- stable relationship w host - lysogeny - most viral genes not expressed
- still a virus but not a virion
- can revert to lytic pathway
2
Q
what are the 2 options for how viral dna is integrated into host, what does it rely on
A
- into host chromosome like lambda phage
- or as a plasmid like P1 phage
- repressor - if deactivated or not synthesised leaves lysogeny and enters lysis
3
Q
what is a prophage
A
viral genome integrated into host genome
4
Q
how does lambda phage integrate its dna into host genome
A
- lambda phage dna has overhanging ends called cos that recognise and bind to each other - circular in host
- integrates at attachment site att(lambda)
- double nick (not at cos sites) of both viral dna strands and host dna
- requires lambda integrase enzyme to insert into host chromosome
- dna ligase seals gaps
5
Q
lytic pathway: rolling circle replication
A
- synthesises long, linear concatamers of DNA
- one dna strand of circular lambda genome is nicked
- long ss concatamer is made from broken strand, using unbroken strand as template
- ds, using new ss as template
- ds concatamer cut into genome sized chunks at cos sites - cohesive ends
6
Q
what type of rna cant be translated in eukaryotes
A
polycistronic
7
Q
what sort of eukaryotic viruses have + strand rna, what is + strand rna
A
- typically v small, except coronaviruses
- eg poliovirus, rhinovirus, hepatitis A
- is like mrna, can be directly translated into proteins
- but + is converted to - as an intermediate to synthesise more +
8
Q
info about poliovirus, genome, dif w mrna, how this is overcome
A
- single linear ssRNA genome
- genomic rna acts like mrna (+ strand) but theres no capping
- instead 5’ end folds into stem loops and binds to Vpg protein, which mimics a cap
- does have poly a tail at
9
Q
poliovirus protein synthesis
A
- genomic rna acts as mrna
- viral protein is synthesised as one large polyprotein the chopped into functional units
10
Q
poliovirus rna replication
A
- host cant copy rna from rna. so virus makes its own rna replicase enzyme
- strand synthesised to make + strand from
11
Q
poliovirus replication - where, what from host is destroyed
A
- occurs in cytoplasm
- doesn’t involve dna
- host rna and protein synthesis inhibited - host cap binding complex is destroyed
12
Q
why do viruses synthesise polyprotein
A
conserve limited genome space - dont need multiple primers etc
