Introduction to Virology Flashcards
Are viruses living?
No, they lack the essentials of life
Which essentials of life do viruses display?
Protecting contents from external environment
Evolve by natural selection
Which essentials of life do viruses not display?
Ability to take up energy and make use of it
Transport of cell; into cell; within cell
Reproduction of self
Why are viruses obligate parasites?
They must have a host cell to reproduce
Where are the highest mutation rates found and why?
In the smallest genomes
They are less likely to correct mistakes in DNA replications due to less enzymes
What does a virus need?
To be able to enter a host cell
Have the host cell replicate the viral genetic material
Have the host cell transcribe and translate the viral genes
What can happen once all the virus components are made?
The infectious viral particle, the virion, can be assembled
What was the fatality rate of yellow fever?
20%
How is yellow fever transmitted?
Mosquitos
What are River’s postulates?
- Isolation of virus from diseased hots
- Cultivation of virus in host cells
- Proof of filterability (confirms small size)
- Production of a comparable disease when used to infect experimental animals
- Re-isolation of the same virus from the infected host
- Detection of a specific immune response to the virus
What is the general strategy that all viruses follow?
They package their genomes into a particle that mediates transmission from host to host
A virus genome contains the information for an infectious cycle within a susceptible permissive cell
All viruses are able to establish themselves in a host population so that their survival is ensured
What did Hershey and Chase prove?
DNA is the genetic materail
How do viruses protect their genetic material?
Protected by capsids
Resistant to proteases, heat, or temperature extremes
Uses as few proteins as possible
Which viruses are more susceptible to the environment?
Enveloped viruses
What does the arrangement of nucleic acid and protein cost in tobacco mosaic virus look like?
The RNA assumes a helical configuration surrounded by the protein capsid
The information for assembly is contained within the protein-structure itself
This process is called self-assembly
Why do capsids use as few proteins as possible?
Makes syntthesis easier
What is the viral lifecycle?
Attachment = use a variety of receptors
Penetration = crossing the membrane
Utilization = host cell proteins/enzymes needed for replication, transcription, translation
Biosynthesis = synthesis of proteins
Assembly = progeny particles are produced
What is the life cycle of an enveloped RNA virus like?
The viral envelope membrane fuses with the host cell membrane to allow entry
RNA is transcribed and replicated using viral enzymes
The virus can leave the cell by budding off which takes some of the host cell membrane with it
How does the membrane help the virus hide from our immune system?
It is of host origin
Contains host proteins
Why is viral growth exponential?
Viruses synthesize progeny de novo and release a large number at once
How many poliovirus particles are released in 24 hours?
1-50,000
How is viral titre determined?
A dilution is mixed with bacteria and melted agar
Pour onto an agar plate
Phage plaques make holes in the lawn
What is the unit used to report virus titre?
Plaque-forming units/mLd
What is viral classification based on?
The nature of the genetic material
Symmetry of the capsid
Presence of an envelope, dimensions
