2-2 Virus Life Cycle Flashcards
What are the basic requirements for virus replication? (6)
- The right host (tropism)
- A host cell with the right receptors (susceptibility)
- Appropriate intracellular environment (permissiveness)
- Biosynthesis machinery
- Abundant macromolecule building blocks (nucleotides, amino acids, ATP, sugars, lipids, etc.)
- Time to finish replication (cells may kill themselves to stop viral growth)
List the steps in virus replication (9)
- Recognition
- Attachment
- Penetration
- Uncoating
- Transcription
- Translation
- Replication
- Assembly
- Lysis and release (Egression)
Describe the 3 phases of a single-step virus growth curve
- Eclipse: Includes virus replication and assembly…no virus is recovered during this phase
- Maturation and Release: Virions are made and can infect other cells
- Burst size: the number of infectious viral progeny from a single round of replication
What are the 4 possible ways that virions can enter into cells?
Englufment of the entire virion into the cell by:
1. Pinocytosis
2. Phagocytosis
3. RME (receptor-mediated endocytosis)
Conversely, the virus can also enter the host cell by:
4. Fusion of the viral envelope with PM
Why do virions need to “uncoat”?
For infection to begin, capsids must open to release the genome into the cytoplasm or nucleus…uncoating marks the beginning of the Eclipse phase
Describe the viral genome
All viruses must be able to make viral mRNA either via viral or host polymerases. The viral genome is the template for transcription, and viral and/or host transcription factors regulate mRNA synthesis to create VIRAL proteins.
How does the capsid uncoat?
host cell enzymes “pull” capsid open
I think host cell enzymes actually degrade the capsid via proteases etc. but Moffat said the word “pull”
What is RDRP
RNA-dependent RNA polymerase (RDRP) is an essential protein encoded in the genomes of all RNA-containing viruses with no DNA stage that have sense negative RNA, i.e. only RNA viruses.
Replicates RNA from RNA (usually you make RNA from DNA)
T/F: Capsid assembly can occur at the same time as envelopment
True
How do virions get out of cells?
Budding
Exocytosis
Cell lysis
cell-to-cell spread
What are PFUs?
Plaque-forming-units.
Virus egress lyses cells…lysed cells appear clear when cell monolayers are stained with dye and you can out viruses with a plaque assay to calculate burst size
What is meant by the term host range?
the preferred species (that a virus can infect)
what is mean by the term tissue tropism?
the preferred cell type
What is meant by susceptible?
What is meant by permissive?
Susceptible cells are those that a virus can enter.
Permissive cells are those that support virus replication and virion synthesis.
