RNA Viruses 1

Question 0

RNA-dependent RNA polymerase (RDRP)

Answer 0

Allows RNA viruses to copy RNA genomes and synthesize mRNA from RNA templates

Works in cytoplasm except in influenza virus
RNA, RDRP, nuceoproteins, accessory proteins not free floating in cytoplasm, often on cell membranes (endosomes, lysosomes, ER, vesicles) to concentrate components so higher efficiency

Fidelity is low, no proofreading, mixtures of wild type and mutant forms

Host cells don’t have these enzymes to transcribe RNA from RNA
All RNA viruses encode RDRP but (-) RNA and dsRNA viruses must package RDRP in virion while (+) RNA viruses may or may not package RDRP in virion (must make RDRP before replication can begin)

(-)strand is antisense strand/template for mRNA
(+)strand is sense strand/same as mRNA

Question 1

Features of RNA viruses

Answer 1

RNA is genetic material and template for protein synthesis

Has RNA-dependent RNA polymerase

Rapid evolution by recombination

Reassortment of genome segments in segmented RNA viruses

Mutants arise frequently, new variants means new diseases, drugs and vaccines lose effectiveness

Quasispecies: viruses are mixture of populations of mutants

Question 2

Polio virus disease Transmission

Answer 2

Fecal-oral, persists in water supply, infects only humans

Infects GI epithelial cells and may spread to muscles and neurons

Pathogenesis:
95% asymptomatic acute GI infection
5% mild disseminated disease
1% paralytic infection of motor neurons

Question 3

Poliovirus

Answer 3

Enterovirus

(+)ssRNA, linear RNA molecule, (+) RNA can be immediately transcribed to mRNA but (-) RNA needs to be converted to (+) RNA before trancription

Replication: Virion binds CD155 receptor, capsid protein forms pore through membrane, uncoating after entering through endocytosis, RNA genome enters, has VPg protein on RNA that is recognized by host ribosomes, transcribed into poly protein that is chopped up into smaller proteins (translation happens when RDRP is scarce)

Transcription: (-)RNA synthesis occurs in vesicles to make more (+)mRNA when RDRP is abundant

When capsid proteins accumulate, new mRNA is packaged