Magor- Lecture 1: Virus Flashcards
What is the size of a virus relative to a bacterium?
Viruses are small (30-90 nm)
Bacterium ~ 1 micron
Is a virus a living thing? Why or why not?
No. Viruses lack the essential of life
Give two facts about a virus
- Protecting ‘contents’ from external environment
- evolve by natural selection
Are viruses able to take up energy and make use of it?
No
Are viruses able to transport- of cell; into cell; within cell?
No
Do viruses reproduce themselves?
No
What makes viruses obligate parasites?
They must have a host cell to reproduce
Viruses have highest mutation rates in ________ genomes
smallest
Virus is a latin word meaning ______
poison
3 things a virus needs
- 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 happens once all the virus components are made?
Once all the virus components are made the infectious viral particle (virion) can be assembled.
In 1901, they identified the first human virus ______________
yellow fever virus
He is a Cuban scientist who linked yellow fever to mosquito transmission in 1881?
Carlos J. Findlay
He went to Cuba to test the theory of mosquito transmission
Dr. Jesse Lazear
Lazear never directly admitted to experimenting on himself but Reed reviewed Lazear’s sketchy notations that he evidently found entries strongly suggesting Lazear’s case was not accidental.
He used army volunteers to prove mosquitoes transmitted yellow fever virus.
Dr. Walter Reed
She is a US army nurse who agreed to be infected twice but didn’t survive the 2nd infection, which means the virus probably shuts down some immune memory
Carla Maass
What is the yellow fever case fatality rate
20%
This disease is known since the 1700s-caused by ‘miasma’ although convincing descriptions date back to Hippocrates (2400 years ago)
Influenza
What year was the first identification of human influenza?
1933
Why are ferrets good animal model for influenza research?
Because they have similar symptoms that humans have (ie. sneezing)
Egg allantoic fluid
- this is what we use now to recover viruses and grow viruses used for vaccines
- the eggs have been fertilized and incubate for about 10 days. The chick is starting to grow in that egg in 10 days. You can infect that membrane and fluid around the egg
River’s Postulates (modified Koch’s postulates) - how you workout what caused the disease.
What are the 6 postulates?
- Isolation of virus from diseased hosts (harder than it seems because lots of viruses have self-limiting infection)
- Cultivation of virus in host cells
- Proof of filterability (confirms small size; tells you that the causative agent is not a bacteria, it is possibly a virus)
- Production of a comparable disease when used to infect experimental animals (host animal or related)
- Re-isolation of the same virus form the infected host
- Detection of a specific immune response to the virus
Case study: a patient is referred to you from airport heat screening.
What viruses can be detected by the fever they cause?
Coronavirus
Why might a viral infection go undetected by airport heat screening scanners?
It could be the virus caused the before before or after they’re still infected.
All viruses follow a general strategy: (3)
- They package their genomes inside 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
Do viruses intent to kill their hosts?
No, viruses don’t intend to kill their hosts
Capsid (protein sheath)
protects the nucleic acid
viruses are covered with this
Their experiment in 1952 proved that DNA is the genetic material
Hershey and Chase
Both of these viruses have a capsid but they also have a membrane around their surface
Influenza and Coronavirus
This protects the genetic material of the virus. It is resistant to all kinds of environmental factors
Capsid
Viruses that don’t have a membrane such as the Tobacco mosaic virus (TMV) are
Very resistant to anything - proteases, heat or temperature extremes
uses as few proteins as possible
Enveloped viruses such as HIV, Coronavirus, Influenza are
much more susceptible to the environment
they have that membrane and that membrane can’t dry out. If the membrane dries out, that virus is no longer viable and able to infect cells.
Arrangement of nucleic acid and protein coat in tobacco mosaic virus
- The RNA assumes a helical configuration surrounded by the protein capsid.
- The information for assembly is contained within the protein structure itself (self-assembly)
Self-assembly
- A process that a lot of viruses do
If you put the structural subunits (protein) and virus RNA in a test tube together, it automatically assembles.
How does the virus ‘know’ how to assemble?
All of the things that are necessary for the correct assembly of this protein host and the RNA strand that it coats are inherent in the structure of that protein.
Packaging and structure of poliovirus proteins in the capsid
- uses 60 copies of each 4 proteins to generate the icosahedral shape
- assembly uses as few proteins as possible-easier synthesis
- capsid only for norovirus-persistence in the environment
How does poliovirus leave the cell?
Poliovirus leaves the cell by rupturing. They’re gonna synthesize 50,000 copies of itself in 24 hours
Simplified viral life cycle steps (5)
- Attachment -viruses 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
Life cycle of an enveloped RNA virus (Measles, CoV, Influenza)
- The viral envelope membrane fuses with the host cell membrane to allow entry.
- RNA is transcribed & replicated using viral enzymes.
- Virus can leave cell by budding off, taking some host cell membrane with it.
What is the source of the enveloped for enveloped viruses?
The host cell
How does the membrane help the virus hide from our immune system?
a. it is of host origin
b. contains viral proteins
c. contains host proteins
d. a & c are correct
D
Viruses replicate via _________ growth
exponential
Viruses synthesize progeny de novo and release a large number at once
eg. Poliovirus 1-50,000 particles in 24 hours
How is the viral titre determined or how much virus is present?
Using a plaque assay
- A dilution is mixed with bacteria and melted agar
- Pour onto agar plate
- Phage plaques make ‘holes in lawn’
What is the virus titre? Concentration reported as:
a. bacteria/mL
b. viruses/mL
c. plaque forming units/mL
d. particles/mL
C
Virus classification is based on: (3)
- the nature of the genetic material
- symmetry of the capsid
- presence of an envelope, dimensions
Virus genetic material can be:
DNA or RNA (single stranded or double stranded)
Examples of RNA viruses
Norovirus
Polio
HIV
CoV
Influenza
Measles
Examples of DNA viruses
Herpes
Pox
