Basics/RNA viruses Flashcards
What three basic gene units are found in all viruses?
Capsid protein (structural proteins), replicon, host cell interacting factors
In approximately what order of magnitude are viruses present in and how do you view them?
10 x -7 ; view by electron microscope
How do you classify viruses?
Host cell kingdom (eukaryotic vs prokaryotic), genome type of virus, virus structure (enveloped or naked, capsid shape)
What are the virion components from inside the virion to outside the virion?
Genome, nucleocapsid (coats genome), capsid (also known as core), tegument (mixture of viral and cellular proteins), matrix, envelope (plasma membrane from host), glycoproteins
Definition of a virus
capsid encoding organism
Definition of a capsid
protein shell surrounding nucleic acid genome
How do you view the effects of a virus?
In culture some viruses might cause cytopathic effects on infected cells causing these cells to ball up and form plaques; use an inverted microscope
What does a virus need to grow? (there’s 6)
the right host (tropism), a susceptible host (cell has the right receptors), the right environment (permissible), host cell machinery, abundance of building blocks, adequate time
What are the steps in viral replication? (generally)
- recognition 2. attachment 3 entry (penetration or fusion) 4. uncoating (beginning of eclipse phase) 5. Transcription of mRNA 6. Translation 7. Replication of genome 8. Assembly of virion (end of eclipse phase) 9. Egress (budding/exocytosis/lysis/cell-to-cell fusion/synctium formation)
What is the eclipse phase?
Phase where the virion is undetecable- begins when the capsid is broken down or uncoats
Common features of RNA viruses
Most never enter the nucleus
Require RDRP to replicate the genome/transcribe mRNA
RNA is the template for both replication and mRNA
The (+) strand is the coding or sense strand
(-) ssRNA and dsRNA require RDRP to be present in the tegument as well as in the genome
(+) ssRNA may not have RDRP in the tegument and the first step is therefore translation to make RDRP from genome
RNA viruses have a high mutation rate because RDRP doesn’t proofread and works very quickly
Why is it hard to make a vaccine for RNA viruses?
Really high mutation rate with RDRP, both wildtype and mutant forms are present at all times, recombination is a high frequency event (gets chunks of RNA being exchanged), reassortment of genetic segments (can get a new variant that is more virulent)
How is polio virus classified?
(+)ssRNA, naked, icosahedral, eukaryotic (only infects humans
What cells does polio virus infect and how is it transmitted?
Attaches to CD155R on enterocytes in GI tract; transmitted by the fecal-oral route and can persist in water. In most people asymptomatic (still shed); 5% get disseminated infection, 1% get paralytic infections (mutation changes tropism)
What is a potential issue for (+) ssRNA viruses? How is it solved?
Both RDRP and translation occur at the same time and can collide- if this happens (early in infection) then translation first and then replication (get more (-)ssRNA when RDRP is more abundant)
