17 - Virology Flashcards
Viruses are the smallest _______________
self-replicating organisms
They have no ___________, they are obligated to invade cells and hijack the cellular machinery
independent metabolism
Viruses can consist solely of a small segment of ________________ encased in a simple _____________
nucleic acid
protein shell
T or F: There is an ongoing debate if viruses constitute life or not
T
Positive-sense viral RNA is similar to _____ and can immediately be _______ by the host cell
mRNA
translated
T or F: Purified RNA of a positive-sense virus can directly cause infection, although, it may be less infectious than the whole virus particle
T
Negative-sense viral RNA is complementary to the _______ and thus must be converted to ____________ by a RNA ___________ before translation.
Purified RNA is not infectious by itself
mRNA
positive-sense RNA
polymerase
Viruses containing ambisense single-stranded RNA genomes are grouped under ________________________
Ambisense means that the virus resembles a __________ sense RNA virus, however they can also translate genes from the _______ strand
negative sense single-stranded RNA viruses
negative
positive
Give the characteristics (3) of enveloped viruses:
- have lipid-bilayer membranes
- impermeable barrier between their genomes and the outside environment
- ex: HIV, influenza
Give the characteristics (3) of non-enveloped viruses:
- no membranes
- no barrier, therefore require a tightly packed protein shell to exclude nucleases or other sources of genetic damage
- ex: poliovirus / papillomavirus
The virus binds to the surface of receptive host cells and entry is initiated by: (3)
- inducing conformational changes in the virus that lead to association with other receptors, membrane fusion, and penetration
- transmit signals through the membrane prepares the cell for invasion
- induction of the endocytic pathway
T or F: viruses can only infect cells to which they can bind
T
The virus triggers the penetration process and enters the __________
cytosol
DNA viruses are transported to the nucleus for genome __________ or __________
uncoating or replication
T or F: Several viruses have developed mechanisms to allow them to deliver their DNA to the nucleus?
T
RNA viruses may be translated in the_______
cytosol
Viruses rely on functions provided by their _______
host cells
Almost all viruses encode and express unique ________ including ________
proteins
enzymes
RNA viruses must replicate their genomes one of 2 unique ways:
1) RNA-dependent-RNA synthesis (RNA replication)
2) RNA-dependent-DNA synthesis (reverse transcription) followed by DNA replication and transcription (ex: retroviruses)
All viruses must eventually express their genes as _______________ early in infection to make essential viral ___________
functional mRNA
proteins
mRNA is always defined as _____________ and its complement is negative-sense
positive sense RNA
Each type of virus will have different strategies to make mRNA dependent upon their starting ___________
genetic material
Each of the viral replication pathways will require different enzymes : if it is an enzyme that the host encodes the virus will use the ___________ enzyme. If it is an enzyme that is not included in the host biology the virus must _______________
host encoded
encode its own enzyme
What is the issue with the polymerases that catalyze RNA replication and reverse transcription?
-They have minimal proofreading activities
Name the 4 important foodborne viruses:
1- Poliovirus
2- Hepatitis A virus
3- Norovirus
4- Rotaviruses
RNA-dependent RNA polymerases (RdRp’s) and reverse transcriptases have an error rate that is _____ orders of magnitude higher than DNA-dependent DNA polymerases
three
RNA viruses evolve at a much faster rate than their ____
host
*this means that the viruses sometimes can escape from host produced neutralizing antibody
____________ are transported to a point in the host cell where they can be assembled into a viral particle
Macromolecules
Most viruses rely on the ____________ for biosynthesis of their macromolecules as well as for intracellular sorting and delivery of macromolecules to the site of virion assembly
eukaryotic cell
Because the same sorting mechanisms that the cell uses for it’s own molecules is used the viral macromolecules must also possess similar ___________
targeting signals
Explain the main steps in virus assembly:
- proteins must be transported to the plasma membrane must travel through the secretory pathway of the cell
- they associate with the endoplasmic reticulum and are translocated across via a proteinaceous pore
- these proteins can then be transported to the golgi complex and onto to the plasma membrane unless they contain AA motifs that localize them to another location
Intracellular transport occurs in ______________
coated vesicles
Non-enveloped viruses can assemble in the ________ or the ___________
cytoplasm
nucleus
For non-enveloped viruses structural proteins must be retained at the _________________ where assembly occurs
subcellular domain
Enveloped viruses must acquire a ______________ from a host cell membrane during assembly
lipid bilayer
Explain the virus assembly for a non-enveloped virus:
1- macromolecules assemble into empty capsids
2- viral DNA is inserted into the structure via a packaging sequence at one end of the genome
3- precursor core proteins are also packaged into the empty capsid along with DNA
4- proteolytic cleavage of the precursor proteins by proteinase yields the mature (infectious) virion
What are the 3 pathways of enveloped virus assembly ?
1- proteins are transported to plasma membrane and assembly of the capsid and envelopment occurs simultaneously
2- capsid assembly occurs in the cytoplasm and then the virus buds from the plasma membrane and gets its envelope
3- capsid assembly occurs in the cytoplasm and gets its envelope from the ER and is exported via exocytosis
Glycoproteins are transported to the preferred lipid bilayer of whichever virus is involved: (2)
- plasma membrane
- endoplasmic reticulum
Viral capsid develops elsewhere in the cell, nucleic acids are packaged in the capsid and transported, in ______________, to the area where the envelop will be acquired
endosomal vesicles
In the case of the ER the enveloped virion is transported to the plasma membrane via the ______________
transport vesicle
T or F: enteric viruses are an important cause of foodborne illness in Canada and other countries
T
Foodborne enteric viruses are hard to ___________ and hard to recover from contaminated foods (most are not __________)
detect
culturable
What happens to foodborne enteric viruses in food systems?
they do not multiply in food systems, some die off rapidly during food storage and preservation
Are foodborne enteric viruses excreted in high numbers in human feces?
yes
What can kill enteric viruses:
- pasteurization
- heat
- irradiation
T or F: foodborne enteric viruses can multiply outside the human body
F, they require human cells to multiply
