Virology Final Part 4 Flashcards
What is the structure of the influenza virus?
Enveloped, (-) sense segmented RNA genome, pleomorphic, each segment of RNA separately encapsulated with several copies of the NP and has own polymerase complex
What proteins are embedded on the influenza virus envelope?
Hemagglutinin, neuraminidase, matrix protein
What is the function of H protein on the influenza virus?
Attachment to the host cell
- release of the viral RNA into the cell by causing fusion of viral and cellular membranes
What is the N protein for on the influenza virus?
Release from the host cell?
What is the function of the matrix protein?
Allows H+ to enter— important for uncoating
How are each of the segments of the influenza genome organized?
Each is organized into a ribonucleoprotein (RNP)
What is the structure of a RNP?
RNA coated with NP and packaged with RDRP
What makes up the RDRP complex?
PB1, PB2, PA
What is the host’s virus receptor for influenza? What is the anti receptor?
Sialic acid; hemagglutinin
Why is influenza preferential to humans?
The human anti-receptors fit better with human SA
Why are pigs mixing vessels for influenza?
They have two forms of SA on their cells
Most human influenza illnesses are due to which H types?
1, 2 and 3
How do you name an influenza strain?
- antigenic type
- (sometimes host of origin)
- geographical origin
- strain number
- year of collection
- virus subtype
What is the function of tryptase Clara?
It cleaves H0 to form H1 and H2 so it will undergo a pH dependent change and reveal the fusion peptide
Where is the influenza genome replicated?
In the cells nucleus
What two modifications are needed for the virus to get its genome into the cytoplasm?
- Tryptase Clara cleaves H to reveal fusion peptide
- pH dependent change in the endosome allows H to unfold so the fusion peptide inserts into the endosome membrane
- H+ enters the cavity and separates the RNPs from the matrix protein
What must the virus do so that it can replicate and transcribe its genome?
- has pre-formed RDRP packaged inside
- has a gene that encodes the RDRP
How does influenza generate mRNAS that can compete for access to the ribosome?
- cap stealing from cellular mRNA and a primer to provide the 3’OH group
- the viral genome has a signal to construct poly(A) tail on the mRNA
- the cellular mRNA is destroyed when the virus steals the cap to synthesize its own mRNA— eliminates competition
What does influenza need to encode?
- RDRP, structural proteins, envelope proteins
How do the genes get split apart?
The fragments with two genes use the cell’s splicing enzymes to modify RNA so that its monocistronic
What are the two types of (+) RNA that influenza synthesizes during its replication cycle?
Incomplete and complete
What is incomplete RNA?
- mRNA needed for protein synthesis
- made early in the replication cycle by stealing 5’ caps
What is complete (+) RNA?
- a template to replicate the genome
- made later in the cycle and not used as mRNA
- the alternate conformation of the RNA POL does not require a primer
What are the two conformations of RNA POL?
- Open: conformation for making mRNA, needs a primer
2. Closed: for replicating the genome, no need for primer
What are the three sites on the open conformation of the RDRP?
- endonuclease (cleaves polypeptide chain)
- Binding of the 5’ end of the template
- Site that reads the template and synthesizes the mRNA
How does cap stealing work?
- the polymerase complex binds a host cell mRNA by its cap, and the endonuclease cuts the cap off the mRNA
- the mRNA stays on the complex and is used as a primer
How does influenza do mRNA synthesis?
- The polymerase reads the (-) template and adds complimentary nucleotides to the end of the cellular mRNA fragment
How many of the segments undergo splicing after translation, but before it goes to the cytoplasm?
2 out of 8
Where is the mRNA for the H, N and M2 proteins translated? Where is the rest of the mRNA translated?
A ribosome associated with the ER; cytoplasmic ribosomes
What is the first component of the virus that assembles at the plasma membrane?
RNP’s and M1 proteins
What promotes membrane fission?
M2
What controls the release of the virus?
Neuraminidase— cleaves the sialic acid residues from the virus and the host cell
Why does the virus remove sialic acid from the host cell? Why is it removed from the virus?
To ensure the newly release particle does not reinfect the cell; to prevent the virus particles from sticking together
How does an “already infected with influenza” cell die?
Programmed cell death (apoptosis, necropoptosis, pyropoptosis
