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Virology Intro Module 1
What does 'virosphere' mean?
Answer and explanation
Global sum of all viruses and virus-like entities on Earth
Estimated number of virus-like particles in the virosphere?
Answer and explanation
Approximately 10^31
How do viruses compare in abundance to cellular life?
Answer and explanation
Outnumber cellular life by at least 10:1
What does 'virome' mean?
Answer and explanation
All viruses within a specific organism or environment
How many viruses are in the human virome at any time?
Answer and explanation
Approximately 10^13 to 10^14 viral particles
Why don't we get sick from all viruses we encounter?
Answer and explanation
Many viruses have little or no health impact; immunity; not all cause disease
What percentage of RNA virus sequences in human feces resemble plant viruses?
Answer and explanation
More than 90%
What is anelloviruses' relationship to humans?
Answer and explanation
Colonize more than 90% of healthy humans
Give one way viruses can be beneficial.
Answer and explanation
Collapse phytoplankton blooms
Name another benefit of viruses.
Answer and explanation
Regulate harmful gut bacteria
What portion of the human genome is ancient viral DNA?
Answer and explanation
Approximately 8%
What is the escape hypothesis of virus origin?
Answer and explanation
Rogue genetic elements escaped cells and gained mobility
What does the reduction hypothesis propose?
Answer and explanation
Viruses are remnants of complex cells losing genes over time
What is the virus-first hypothesis?
Answer and explanation
Viruses arose before cells from self-replicating RNA molecules
Who developed a porcelain filter that retained bacteria?
Answer and explanation
Charles Chamberland in 1884
What disease agent did Dmitri Ivanovski show passed through filters?
Answer and explanation
Agent causing tobacco mosaic disease
Who named the agent 'contagium vivum fluidum'?
Answer and explanation
Martinus Beijerinck
What year did Wendell Stanley produce TMV crystals?
Answer and explanation
1935
What year were bacteriophages visualized by electron microscopy?
Answer and explanation
1939
Meaning of the Latin word 'virus'?
Answer and explanation
Poison, venom, or slimy liquid
Basic definition of a virus?
Answer and explanation
Small, infectious, obligate intracellular parasite
What is a virion?
Answer and explanation
Complete virus particle
Define a virus capsid.
Answer and explanation
Protein shell surrounding the viral genome
What is a nucleocapsid?
Answer and explanation
Nucleic acid-protein assembly inside virus particle
How do some animal viruses obtain their envelope?
Answer and explanation
Derived from host-cell lipid membrane
What proteins are inserted into the viral envelope?
Answer and explanation
Viral spike glycoproteins
Role of matrix protein in enveloped viruses?
Answer and explanation
Links nucleocapsid to viral membrane interior
Role of virus attachment proteins (spikes)?
Answer and explanation
Bind specific host cell receptors for entry
Example of a virus spike and its receptor?
Answer and explanation
SARS-CoV-2 spike binds ACE2 receptor
List the three basic capsid shapes.
Answer and explanation
Helical, icosahedral, complex
Five ways viruses are classified.
Answer and explanation
Taxonomy, nucleic acid type, capsid symmetry, envelope presence, particle size
Which committee handles virus taxonomy?
Answer and explanation
International Committee on Taxonomy of Viruses (ICTV)
Basis of Baltimore virus classification?
Answer and explanation
Genome strategy for making mRNA
How does viral replication differ from bacterial division?
Answer and explanation
Viruses produce components then assemble; bacteria divide by binary fission
What occurs during the eclipse period?
Answer and explanation
Uncoated viral nucleic acid; no infectious virus detected
Define the latent period in viral replication.
Answer and explanation
Time to replicate and assemble new particles before cell lysis
What happens in the burst period?
Answer and explanation
Host cells lyse releasing mature virions
Describe the plateau period.
Answer and explanation
Extracellular viral titer levels off
List the nine major steps of virus replication in animal cells.
Answer and explanation
Recognition, attachment, penetration, uncoating, mRNA synthesis, protein synthesis, genome replication, assembly, release
Define virus tropism.
Answer and explanation
Ability to infect specific cell types and complete infection
What does cellular tropism mean?
Answer and explanation
Preference for particular cell types
Give an example of viral neurotropism.
Answer and explanation
Rabies virus infects neurons
Define 'susceptible cell' regarding viruses.
Answer and explanation
Has receptor allowing viral entry
Define 'resistant cell' regarding viruses.
Answer and explanation
Lacks receptor preventing viral entry
Define 'permissive cell' regarding viruses.
Answer and explanation
Supports viral replication
What cell type can support viral entry and replication?
Answer and explanation
Susceptible and permissive cells