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85 Cards in this Set

  • Front
  • Back
What does the genome of all orthomyxoviruses look like?
segmented (-)strand RNA genome
How many genera in the family Orthomyxoviruses? What is this based on?
2 (Influenza A/B, Influenza C)
antigenic differences
structural proteins
Do orthomyxoviruses encode and package thier own polymerase?
Where does the transcription and recplication of the genome occur for Orthomyxoviruses?
nucleus of host
Where do Orthomyxoviruses uncoat?
inside the host cell
T/F: Influenza A and B are morphologically distinguishable
How are influenza viruses typically transmitted?
respiratory route
Describe the Influenza A/B genome
8 segments of ss(-)RNA
Describe the Influenza C genome
7 segments of ss(-)RNA
__ of the Influenza A/B genome segments code for ___ protein(s). The other ___ code for two proteins.
What are the genome segments of Influenza A/B called?
How many amino acids does NP bind?
What is the most common protein in the RNPs?
What does the Influenza A/B RNA polymerase complex consist of?
PB1, PB2, PA
What are the four different proteins in each RNP?
What is Influenza A/B's morphology?
highly pleomorphic
commonly spherical or ovoid
80-120 nm in diameter
enveloped with viral glycoproteins embedded
Is Influenza A/B enveloped?
how big is Influenza A/B ?
80-120 nm in diameter
What are the two types of glycoproteins in the lipid envelope of Influenza A/B ?
Hemagglutinin (HA)
Neuraminidase (NA)
What is the structure and function of HA?
trimer of identical subunits
used in attachment
What is the structure and function of NA?
tetramer of identical subunits
used in detachment
There are about ___ copies of the glycoproteins in the lipid enveloped of Influenza A
There are approximately ___ HA to every NA
What does HA do to red blood cells?
agglutinates them
In the lipid envelope there is an ion channel protein called ___, which is involed in the uncoating process
The ___ (__) protein lines the inside of the lipid envelope
matrix (M1)
What is the most abundant Influenza A/B viral protein?
What is the function of M1?
allows the nucleocapsid, envelope, and glycoproteins to assemble correctly
What is the Influenza A host range?
humans, animals, birds (pigs and birds particularly important reservoirs)
What is the Influenza B host range?
only humans
What is the Influenza C host range?
only humans
Does Influenza C cause disease?
it is not thought to
What is the host cell receptor for influenza virus?
N-acetylneuraminic acid (NANA or sialic acid) residues on mucoproteins
Where is NANA located?
on mucoproteins
What is the natural habitat forinfluenza virus ?
What is the first step in influenza virus replication cycle?
HA cleaved extracellularly by the protease "tryptase Clara"
Where does tryptase Clara come from?
Clara cells of the bronchiolar epithelial cells
What activates the HA, so that it can bind to NANA residues?
cleavage by tryptase Clara
HA binding to NANA residues is thought to be high affinity (T/F)
F. It is thought to be low affinity, but high avidity because of multiple weak interactions
The influenza virus enters the cell by invagination of the plasma membrane to form ___-coated pits. What is this process called?
receptor-mediated endocytosis
What happens after the clathrin coat is removed, during invasion of host cell by influenza virus?
vesicle fuses with an endosome (which has low pH)
What does exposure to low pH trigger, during invasion of host cell by influenza virus?
a second conformational change in HA, allowing envelope of the virus to fuse with the membrane of the endosome
The second conformational change in HA leads to what? What triggers this process?
release of the genome segments into the cytoplasm

the low pH inside the endosome
How do the released RNPs enter the nucleus, during invasion of host cell by influenza virus?
specific targeting sequences in the NP protein allow entry through the nuclear pore
Where is viral mRNA synthesized, during invasion of host cell by influenza virus?
in the nucleus
What are used as primers during synthesis of the viral mRNA, during invasion of host cell by influenza virus?
the capped 5' ends of the host cell pre-mRNAs and mRNAs
During mRNA synthesis, influenza virus uses the cellular RNA polymerase (T/F)
F. It has its own.
Describe the process of "Cap Stealing" employed by influenza virus
The viral RNA polymerase complex attaches to the 5' end of cellular mRNA. It then degrades everything but the 5' cap and about 13 nucleotides
The viral RNA polymerase complex synthesizes the (_) strand using the (_) strand as template, adding the complementary nucleotides to the "stolen cap"
The RNA polymerase complex read the (-) strand in the __->__ direction while synthesizing in the __->__ direction
What is the approximate difference in length between viral mRNA and full-length RNA, during invasion of host cell by influenza virus?
15-22 nucleotides
Why is the viral mRNA shorter than the full RNA, during invasion of host cell by influenza virus?
the viral (-) strang has a 'panhandle' structure at the 5' end that functions as a terminator
What are the two advantages of the cap-stealing method employed by influenza?
mRNA produced can be translated by cellular ribosomes (because it has the h' methylated cap and the poly-A tail)

host cell mRNA is degraded (less competition for ribosomes)
T/F: none of the influenza mRNAs need to be sliced
F. some do need splicing in the cytoplasm
The viral mRNAs that specify viral ___ proteins are translated by the ER-bound ribosomes, whereas all the other mRNAs are translated by cytoplasmic ribosomes
Where are newly synthesized PA, pB1, PB2 and NP proteins transported to?
What is the function of newly synthesized PA, pB1, PB2 in the nucleus?
they catalyze synthesis of the genomes for progeny

(+) strands are made first, then (-) strands are made from these
What causes the cessation of viral mRNA synthesis and induces export of the progeny nucleocapsids into the cytoplasm?
binding of M1 to newly snythesized (-) RNA
What results from M1 binding the newly synthesized (-) strand RNA inside the nucleus?
transport of progeny nucleocapsids into the cytoplasm
Which proteins are transported to the cell surface, to become incorporated into the plasma membrane?
HA and NA
The virion nucleocapsids associate with the __ proteins and the ___ protein and are transported to the cell membrane to associate with the spike proteins
T/F: Influenza lyses the cell to escape
F. It buds off
What is the exact function of NA during exit of influenza?
remove the sialic residues from surface of infected cell to free the virus particle
replication and transcription is done in the ___ and translation is done in the ___ during influenza invasion
For an influenza virus to be infectious, it must have one copy of each segment (T/F)
What causes the HA fusion peptides to insert in the endosomal membrane during the first stages of invasion by influenza virus? What results?
acidity of endosome
dissociation of RNPs from M1, release of RNPs
Does the synthesis of a complete (+) strand (to use as template for (-) strand) involve the RNA polymerase complex?
Does creation of the full-length (+) RNA template involve cap-stealing?
What may regulate the switch to full-size (+) RNA production?
amount of 'free' NP present
T/F: The RNA polymerase complex seems to 'acquire' the ability to initiate RNA synthesis without a primer
T/F: Influenza can be spread by direct contact
Why are influenza virus infections usually limited to URT?
this is the only location where Clara cells are found
How long does the acute respiratoy illness last (influenza)?
3-7 days
What is the common cause of death during influenza infection?
opportunistic pathogen such as Hemophilus influenzae or Staphylococcus aureus
Influenza is shed in high amounts about __ hours after infection
What is the influenza naming convention?
A/USSR/strain#/year of isolation (H_N_)
HA and NA glycoproteins can change in two ways, what are these?
antigenic drift
antigenic shift
Define antigenic drift
minor changes due to accumulation mutations (caused by lack of proof-reading in RNA polymerase)
Define antigenic shift
genetic reassorment of two or more viruses that have simultaneously infected the same cell
How is influenza virus cultivated for vaccine production?
embryonic hen eggs
How are new vaccines produced?
genetic reassortment to produce strain with desired HA/NA antigens
How is the virus inactived during vaccine production (influenza)?
What are the three vaccines for influenza currently in use?
whole (inactived)
subvirion (purified virus treated with detergent to solubilize envelope)
surface antigen (isolated HA and NA glycoproteins)
Where are the epitopes found in influenza virus?
the HA and NA proteins
What is the main approach in terms of antiviral drugs for influenza?
NA inhibitors: (Oseltamivir (Tamiflu), Zanamivir (Relenza) and GS 4104

effective for A and B