INFLUENZA Flashcards
What kind of genome does influenza have? How many types of virus are there?
Segmented (-) RNA: 10 genes distributed onto 8 pieces of (-) RNA (6 code one protein each, 2 code for two each)
- each segment is coated with NP and each has its own RNA POL associated with it
- 4 types: A,B,C,D
What shape is the virus particle? What is the outer structure?
- pleomorphic— most commonly sphere or oval
- lipid bilayer with viral glycoproteins embedded in the membrane (spike)
What are the two types of glycoproteins on the cells surface? What other proteins are there on the envelope?
- hemagglutinin and neuraminidase
- H is a trimer of three subunits and N is a tetramer
- M1 and M2
What are the functions of H and N?
H: attaches to sialic acid to begin replication
N: virus detaches from the host cell by digesting sialic acid after the replication cycle is complete
What is the function of M1?
Line the inside of the lipid envelope and serve to allow the nucleocapsid to assemble correctly during late stages of replication cycle
What is a segment of the genome called? What does it consist of?
- RiboNucleoProtein (RNP)
- (-) RNA, NP, and RDRP (PA, PB1, PB2)
What are the current A subtypes that are circulating in humans?
H1N1, H3N2
Why is influenza common in the upper respiratory tract?
The virus is dependent on tryptase clara (protease in respiratory secretions)
Can the host cell read the virus’ genome as a template?
No, so it must package RNA POL, and also encode it
Where does the virus replicate the genome?
Nucleus
How does the virus enter the cell?
- H0 is modified into H1 and H2 by cleavage by tryptase Clara
- H1 binds to sialic acid, and H2 remains integrated in the bilayer of the envelope (has fusion peptide)
- enters an epithelial cell by receptor mediated endocytosis
- endosome is acidified and H undergoes a conformational change
- fusion peptide is inserted into the membrane and virus genome is released into the cytoplasm
What is necessary for the RNPs to release?
- protons enter through M2 channel in the envelope
- RNPs release from M1
What are the steps for transcription of the genome?
- (-) strand RNA is used as a template for the viral RNA POL to synthesize each of the 8 strands independently
- RNA POL needs a primer, so it steals a 5’ cap from a cellular RNA
- Synthesizes a (+) strand
- POL stutters at the polyadenylation sequence
What are the advantages of cap stealing?
- mRNA that is produced will look very similar to cell’s, so it can be translated by the cell
- Host cell mRNA is degraded and competition is eliminated
Why is mRNA called the incomplete (+) strand?
The entire sequence is not translated
- this is because a panhandle structure is formed when the complex anchors to the 5’ end of the (-) strand
