Intro to Viruses Flashcards
What is the mutation rate for RNA viral replication?
Very error prone bc no proof-reading capability: 10^-3 - 10^-4. Adaptability advantage to virus but problematic to antiviral therapy. ~1 mutation per round of replication
What is the genome type for most DNA viruses
linear double stranded
Name 3 exceptions to the general genome type for DNA viruses
Papovavirus: dsDNA is circular, not linear –> template for both mRNA and genome replication
Parvovirus: ss linear DNA
Circovirus: circular ssDNA
What is notable about the Circovirus
Smallest autonomously propagated virus; circular ssDNA
Two main shapes for viral capsids
Helical, Icosahedral
Where do enveloped viruses get their lipid membrane
Derived from the host cells membrane
How many families of viruses can infect humans
21
Describe Icosahedron symmetry
Nature’s perfect structure: high physical strength and rigidity –> withstand extremes in pH, temp, solvents and can perist outsidde the body
20 equilateral triangles
Examples: adenovirus, poliovirus, Hep A and E
What is the current classification strategy for viruses
Features of viral genome
1) Genome composition (DNA vs RNA)
2) Genome structure and organization
3) Morphology
What is the current virus classification omenclature
Family/subfamily/genus/species/strain
Name the 6 stages of the Viral Lifecycle
1) Attachment to the surface of the target cell
2) Penetration into the cell
3) Uncoating
4) Replication (including macromolecular synthesis events)
5) Assembly of virion components
6) Release of infectious progeny virus
What is the cellular receptor for HIV-1
CD4
What is the cellular receptor for EBV
CD21 (Remember the EBV can cause B cell cancers –> CD21 is a B cell marker)
What is the cellular receptor for Rabies
ACh receptor (remember that all rabies symptoms are all neural and ACh is a molecule of neural synapses)
What is the cellular receptor for HCV
CD81
Name a cellular receptor common to many viruses
Sialic Acid
What is the most important determinant of viral tropism
Cellular receptor type: cells lacking the right receptor are no susceptible to infection
What are the 3 mechanisms of viral penetration
1) Translocation of entire virion across the plasma membrane
2) Endocytosis of the virus particle resulting in their accumulation inside cytoplasmic vacuoles
3) Fusion of the cellular membrane with virion envelope
What step marks the beginning of the eclipse phase? What is significant about this phase
Viral uncoating; during this period no infectious virion can be recovered from the cell –> demonstrated in classical one-step growth experiment
What viruses replicate in the cytoplasm? Exceptions?
RNA viruses and the pox viruses
Exceptions: retroviruses and othomyxoviruses
What viruses replicate in the nucleus? Exceptions?
DNA viruses (except for pox viruses) and the orthomyxoviruses
What enzyme does a dsRNA virus require for replication of the viral genome? What is the product of function?
dsRNA polymerase: mRNA
What enzyme does a negative strand ssRNA virus require for replication of the viral genome? What is the product of function?
ssRNA polymerase: both + and - strand RNA; mRNA
What enzyme does a retrovirus require for replication of the viral genome? What is the product of function?
RNA-dependent DNA polymerase (reverse transcriptase): dsDNA
What enzyme does a DNA virus require for replication of the viral genome? What is the product of function?
DNA-dependent DNA polymerase: dsDNA
What essential genome product must be made by all viruses?
mRNA
Name a family of (+) sense RNA viruses with examples.
Picornaviruses: poliovirus, Hep A, rhinovirus
+ ssRNA can function directly as an mRNA in infected cell –> genome is first translated in order to provide the enzymes needed for replication (doesn’t carry enzymes with it)
Name a family of (-) sense ssRNA viruses with examples.
Orthomyxoviruses (influenza) or Paramyxoviruses (parainfluenza and RSV)
Enzymes needed for mRNA production must be carried in mature virus (ssRNA polymerase)
Name a family of dsRNA viruses with examples.
Reoviruses: rotavirus
Cause significant disease in children
Enzymes for mRNA production must be carried within virion: dsRNA polymerase
Name an example of a retrovirus
HIV
Must carry reverse transcriptase in the virion
HIV acquires its envelope by budding through the cell membrane
Give an example of a dsDNA virus
Herpes simplex virus. Can utilize host RNA polymerases to produce viral mRNA and host DNA polymerases to replicate its genome
What programs viral subunits (nucleic acid, structural proteins and enzymes) to assemble into a compact, arranged virion?
The program for assembly is carried with the PHYSICAL PROPERTIES of each subunit
How are naked viruses typically released from the cell?
Accumulate in cytoplasm and are released during cell lysis
What does “virus morphology” refer to?
The nucleocapsid architecture
Define “replicase”
Complex of viral and/or host proteins required to replicate the viral nucleic acid genome. Include viral polymerases and cofactors
Describe a very unique feature of rotavirus.
Rotavirus is dsRNA. dsRNA is a danger signal to mammalian cells, so capsid proteins are made early and the capsid is partially assembled to keep dsRNA hidden.
What 4 things must retroviruses carry with them in addition to their genome?
Reverse transcriptase
primers
integrase
other enzymes
