10/ viral genetics 3

Question 1

outline - rna as genome, egs

Answer 1

• viruses of animals - rabies, influenza, ebola
• • strand encodes genome but cant directly act as mrna

Question 2

rabies replication

Answer 2

• • rna
• transcription by viral rna pol (rna replicase) into + strand
• translation w host enzymes to viral proteins
• the rna replicase is a type of rna pol which is carried by the virion
• genome packaged and enveloped in host cell memb

Question 3

influenza info - genome, 2 important proteins and 2 enzymes

Answer 3

• • rna is segmented
• influenza A has 8 linear ssRNA molecules (and thats it)
• neuraminidase and hemagglutinin - antigens
• n cuts through sugars of lung so it can escape
• h is a receptor binding protein
• rna endonuclease and rna replicase

Question 4

influenza replication

Answer 4

• viral nucleic acid replicates in host NUCLEUS
• overall pattern same as rabies -
• transcription results in viral mrna w 5’ caps
• primers cut from 5’ end of newly synthesised host mrna by viral endonuclease
• poly A tails added
• viral mrna moves to CYTOPLASM for translation

Question 5

what is antigenic drift

Answer 5

• surface proteins are main immunogenic regions of the virus
• antigenic drift arises from mutations in genes for surface proteins
• so annual vaccination required
• caused by rna from different strains infecting same host and reassorting - new combos

Question 6

HIV genome and replication

Answer 6

• retrovirus - converts rna to dna
• genome has 2 identical strands of
  + ssRNA
• genome replicated through dna intermediate which requires reverse transcriptase
• dna intermediate rather than rna intermediate

Question 7

HIV regions on rna

Answer 7

• R- terminal repeats essential for replication
• gag region encodes structural proteins
• pol encodes reverse transcriptase and integrase
• env codes envelope proteins

Question 8

HIV replication

Answer 8

• fuse w host cell, enter rna
• ssRNA to ds DNA
• integrate into host DNA in nucleus w integrase
• provirus - can stay latent in host genome or cause protein expression

Question 9

HIV gene expression

Answer 9

• in provirus form can be expressed or lie latent
• activation of promoters in LTR region leads to mRNA transcripts that are capped and polyadenylated
• viral mrna either encapsidated (put in virion) or translated
• similarly to polio, polyproteins are synthesised then processed

Question 10

why are polyoma viruses like simian virus cancer inducing

Answer 10

• small t antigen inhibits something in host

Question 10

significance of simian virus 40

Answer 10

• overlapping genes
• genome is in one ds dna circle
• v small genome - relies heavily on host mechanisms
• complexed with host histones, has no viral enzymes
• dif proteins share same sequence w intermediates that are removed
• eg early region encodes both large and small t antigens

Question 11

coding of early and late proteins in the sv40 genome

Answer 11

• single rna made by cellular rna pol from the early region
• this is processed into 2 mrnas, both capped
• introns removed
• expressed t antigen protein binds to origin of replication to initiate genome syntheis
• transcription of late mrna begins at promotor near origin of replication
• late rna processed by splicing, capping, polyadenylation corresponding to 3 coat proteins - VP1, VP2, VP3
• genes for these proteins overlap

Question 12

coronavirus genome, where does replication occur, % of common colds

Answer 12

• single + rna
• cytoplasm like polio
• 15

Question 13

coronavirus structure, no. kb

Answer 13

• enveloped virions
• glycoproteins give crown appearence
• largest rna virus - 30kb

Question 14

coronavirus infection cycle

Answer 14

• genome had 5’ cap and poly A tail - can act directly as mrna
• but only replicase is translated
• the generates - rna copy
• from - copy, several monocistronic mrnas are transcribed and translated into viral proteins
• progeny genomes also produced