Introduction to Virology Flashcards
What is a virion?
The vehicle for transmission of virus genomes to the next host cell or organism. It is the complete infectious form of the virus particle
Virion disassembly into new host cell initiates the beginning of the next infectious cycle
What is the proteinacous coat of a virion?
Capsid - part of virion that encapsulates the viral genome
Nucleocapsid includes the DNA / RNA genome
Some of these can be enveloped with lipids
What is the purpose of virus classification?
Way of predicting properties and pathogenic potential of new isolates
What are the forms of virus genetic material?
- Single or double stranded
- Positive or negative sense (negative will needed RNA-dependent RNA polymerase)
- Non-segmented or segmented
- Linear (DNA or RNA) or circular (DNA)
What is an envelope? What is a virus without an envelope called?
Part of virion which is derived from host cell membranes -> makes it susceptible to degradation via ether
Without envelope -> naked
What are the basic capsid shapes of viruses?
Helical - nucleic acids wrapped inside
Icosahedral - triangular faces, includes threefold, fivefold, and twofold axes
Complex
What is the Baltimore virus classification system?
Based on the fact that ALL viruses must adopt biosynthesis of mRNA prior to being translated by ribosomes. Puts viruses into 7 groups based on RNA synthesis pattern
What are some examples of non-structural proteins which may be packaged in the virion?
Enzymes (i.e. reverse transcriptases or virion polymerases needed for conversion of - sense or RNA back to DNA)
Host-regulators
How many virions are needed to initiate a lytic infection and what is it?
Only one virion -> productive infection making new infectious virions
What is the eclipse period?
interval between when input virion is disassembled and when new infectious virions are produced
What is the burst size?
Number of infectious particles produced per infected cell
What is the time scale of lytic viruses?
From hours to weeks for a single infected cell to finish the cycle and burst
What are the steps of the lytic replication cycle?
- Entry, including attachment, penetration, and uncoating
- Gene expression, including mRNA synthesis and protein translation
- Genome replication
- Assembly / packaging
- Egress / release
What is meant by “host range” for viruses?
The variety of cells which are able to be infected by it
Why are some viruses unculturable?
We haven’t been able to reproduce the exact conditions that house the virus
What are some possible cell consequences of infection?
Transformation or cytopathic effect
Transformation can include immortalization, loss of contact inhibition (no stopping of replication) and ability to form tumors
Cytopathic effect can mean formation of vacuoles / inclusions, lysis, cell death, or fusion (syncytia formation)
What is an incubation period?
The time from infection to first appearance of prodromal symptoms. Varies by virus. Flu is 1-2 days, Rubella is 17-20 days, AIDS is 1-10 years.
What does aerosolization mean?
Virus is so small that it can float in air (i.e. measles).
Ebola is too large to float in air.
How can virus entry / egress vary?
Not all viruses enter and exit hosts by the same route. They have intraorganismal movement
What is a latent infection? Why is this oversimplified?
I.e. HSV, periods where viral titer is very low. This is oversimplified because >50% of HSV transmission occurs during asymptomatic periods.
What is an example of a virus where there is “failure to clear all evidence of infection”
Polio, can stay latently in the GI tract
What is the latent state on a cellular vs organismal level?
Cellular: No infectious particles are produced, but a lytic state can be resumed
Organismal: period between infection and disease reactivation
What is a persistent infection on a cellular vs organismal level?
Cellular: constantly lytic state, equilibrium between cell death and production “smouldering”
Organismal: Continuous inhabitation of host, no matter the mechanism (i.e. HSV). Can include viruses which have latent states.
What is an abortive infection?
One that is non-productive and has no reactivation
