Unit 2 Viruses Flashcards
The study of viruses
Virology
Do viruses only affect humans?
No.
Viralogy began as a science in the late 1800s when infectious tobacco mosaic virus was isolated in a filtered, bacteria-free fluid by
Ivanovski then Beijerinck
This person showed that a human disease called yellow fever was causes by a virus transmitted by mosquitoes
Walter Reed
What did Walter Reed use to filter liquids and trap cellular life?
What did he find
Membrane Filter
Infectious particles still got through the pores and were in the liquid
This term means that viruses are NOT cells. The need a living host to go inside of, and changes to its genome happen over time
intracellular obligate parasites
Are viruses alive?
What is the only property of being alive they have?
No
They have a genome that changes and evolves
The genome of viruses is so small that it needs to use the enzymes/materials of the host cell. What range of meters are viruses in? Bacteria?
Viruses: nm
Bacteria: um
This virus is an exception to the normal size, it is a virus of marine single-celled organisms and has a 730kbp genome
This one has a genome of over 1.2 megabase pairs that encodes 1,200 proteins
This one can be 400nm in diameter, witha 1.2 megabase pair genome coding for 979 proteins
CroV
Megavirus chilensis
Mimivirus
Viruses can be made or DNA OR RNA. Not both. This supports the RNA world hypothesis.
Most viruses are _________
Double stranded DNA
Note: some single stranded DNA, some single stranded RNA, some double stranded DNA
This is a protein shell around the viral genome that is composed of many capsomere proteins
Is it possible to have more than one?
Nucleocapsid
Yes with a large genome
The viral capsid and genome together are called the
nucleocapsid
It is possible for viruses to have an envelope. It can also be considered a
Where does it come from some times?
Plasma membrane
The PM/nuclear membrane/ER of the former host
Is the nuclear envelope similar to PMs we’ve learned about previously?
No.
Why do influenza and HIV have viral envelopes?
It allows them to attach to surfaces and infect host cells
For infection to occur with HIV and influenza, it must be in what type of environment?
Aqueous
All segmented viruses must be
Enveloped
Capsids often exhibit either ___ or _____ shapes
Helical or icosahedral
This type of capsid viral symmetry is spiral, where capsomeres spiral around like a paper towel roll, it is hollow at the center, and is like a rigid rod
Does it have a nuclear envelope?
Helical
Not if its a rigid rod.
This type of capsid viral symmetry looks circular but is actually made of repeating triangles
Does the amount of triangles change if the size of the genome changes?
Icosahedral
No, the triangles just get larger
What type of viral symmetry does influenza have?
What distinguishes it from other versions of these structures?
How many segments are there in its genome?
What is a segment?
Helical
It has flexible rods because it has a envelope
8 segments.
A segment of RNA with its own capsid.
What type of structures are HA and NA? They are located in the envelope of viruses
Spike Proteins
Influenza comes with its own _________ that is used to replicate the genome inside of a host cell
Viral Polymerase
The influenza virus is what type of shape?
Why is it complex?
This structure binds it to the cell wall of other cells and causes shape chang, like a hypodermic needle, to cause injection of a material
Complex
It doesn’t fit neatly into helical or icosahedral
Tail fibers
If a plasma membrane surrounds the nucleocapsid, the virus ______
If there is no plasma membrane, its
enveloped
Naked
What does the acronym APUSSAE stand for?
What does it represent?
Adhere Penetrate Uncoat Synthesis Synthesis Assembly Exit
What must occur in the viral replication cycle
What do naked and enveloped viruses each use to stick to host?
What do they bind to?
Enveloped - spike proteins
Naked - Capsid proteins
They bind to surface receptors on the host cell
What is arguably the most important part in the viral replication cycle?
Entry (penetrate)
Mechanisms for entry vary depending upon the host cell
What do plant, fungal, and bacterial viruses have to contend with that animal viruses don’t?
A cell wall structure
What is the process that a non-enveloped virus uses to enter a host animal cell?
What is the example virus used in lecture?
Endocytosis
Rhinovirus
In the first step of endocytosis of a non-enveloped virus, the virus attaches to the ________
In the second step, endocytosis is initiated.
In the third step, a _______ forms with the virus inside
In the 4th step, the _____ escapes into the cytoplasm and uncoats to release the genome
Cell receptor
Endosome
Nucleocapsid
What are the two methods by which enveloped viruses can enter into a host animal cell?
Membrane fusion
Endocytosis
What virus is used as the example virus in membrane fusion of an enveloped virus?
In the first step, the virus attaches to the _____
In the second step, a _________ in the attachment protein and bound receptor initiates membrane fusion.
In the third step, the viral envelope fuses with the _______
In the 4th step, the ______ enters the cytoplasm and uncoats to release the genome
HIV
Conformational Change
Plasma Membrane
Nucleocapsid
What virus is used as the example virus in endocytosis of an enveloped virus?
In the first step, the virus attaches to the _____
In the second step, ______ is initiated
In the third step, a _____ forms with the virus inside
In the fourth step the _____ of the endosome initiates fusion of the viral envelope with the endosome membrane. Nucleocapsids are released
Influenza
Cell receptor
Endocytosis
Endosome
low pH
Entry into plant cells often depends upon some damage to the plant tissues to open a spot in the
ex) insect feed, wind damage, hail/rain damage, fire damage, human induced damage
Cell wall
For viral entry into bacterial cells, during the first step _____ attach to cell receptors
In the second step, _______ in tail fibers bring the base of the tail in contact with the host cell surface
In the third step, rearrangement of tail proteins allow inner core __________ to extend down into the cell wall
In the fourth step, contact with the PM initiates transfer of DNA through a pore formed in the _____
Tail Fibers
Conformational Change
Tube Proteins
Lipid Bilayer
During entry into bacterial cells, what makes the hole/cuts into the peptidoglycan area?
Which molecule does it come from?
Lysozyme
It is coded by the viral genome
The evolutionary history of viruses isn’t clear, but what 3 hypotheses have emerged/
Coevolution
Regressive
Progressive
This hypothesis of the origin of viruses states that viruses evolved along with their host cells. It is evidenced by the fact the RNA viruses code their own polymerase so that they can persist inside of DNA cells today
This could explain the origin of many ___ viruses
Is there much supporting evidence for this?
Coevolution hypothesis
RNA viruses
No
This hypothesis of the origin of viruses states that viruses are cells that lost some of the replicative and metabolic traits over time
An example of this is that there are some _____ that have no mitochondria, as they have no metabolism because they parisitize other organisms
What doesn’t this explain?
Regressive Hypothesis
Protozoa
RNA viruses
This hypothesis of the origin of viruses states that existing genetic elements gradually gained the ability to move from cell to cell
What provides evidence for this theory?
Progressive Hypothesis
Transposons and retrotransposons
This is also called a jumping gene and is a segment of DNA that cuts itself out and reinserts into somewhere else, evidence of the progressive theory
This is a segment of DNA copied into mRNA, converted by an enzyme back to DNA, and put into DNA in a new position
Transposon
Retrotransposon
What enzyme converts the RNA form of retrotransposons back the DNA?
What is one example of a retrovirus?
Reverse Transcriptase
HIV
Are viruses trickier to work with than bacteria?
Why?
Yes.
They are small and replicate only within appropriate host cells. Also they can’t be seen by the naked eye
There are two types of bacteriophages, what are they?
This type will replicate inside of and burst open (lyse) the host cells
This tape can integrate its genome into the host cell genome (becoming a prophage) and be replicated each time the host cell replicates
Lytic and lysogenic
Lytic
Lysogenic
Which type of bacteriophage occurs temporarily?
Under what circumstances does it get pushed back to the other cycle?
Lysogenic
Lack of nutrients or UV light, aka poor growth conditions
If a culture of bacteria is infected with a bacteriophage and the cloudiness of the vial starts to disappear, what type of bacteriophage is it?
Lytic, the bacteria are dying
What are plaques on a nutrient agar base indicative of?
A clear plaque is
A cloudy plaque is
Bacterial cell death
Lytic
Lysogenic (some cells are still alive)
What was the breakthrough in modern virology that allowed more rigorous study of viruses?
What two things are necessary for tissue culturing?
Tissue Culturing
Nutrients and sterility
The tools for animal virus cultivation helped develop the first human cell line, known as
HeLa cells
Changes that occur in cells due to a cultured virus that can be observed
Why must everything be sterile in this circumstance?
Cytopathic Effects
To make sure that only the virus is acting on the cells
Historically, the names of virus have been uniform or varied?
Varied
What is the current method of viral classification?
What do the letters stand for?
What do they classify viruses based upon?
ICTV
International Committee on Taxonomy of Viruses
Order, Family, Subfamily, Genus, Species (this method is familiar to people)
Another method that was developed based around mRNA production methods
How many classes does it separate viruses into?
Baltimore Classification System
Seven
This type of RNA can act right away to react with ribosomes and code for proteins
This type of RNA has to be changed into a complimentary strand first.
Positive Sense RNA
Negative Sense RNA
The first step in the identification of viruses rests on observations of
Is this method infallible?
morphology
Nope.
What is the best method of viral identification?
What methods are used for it?
What does it specifically study and look for?
Nucleic Acid Analysis
PCR and reverse-transcriptase PCR
Viral evolution patterns
These pathogens are simpler than viruses and consist only of naked RNA, are extremely small (about 400 nucleotides) and have a high degree of internal complementarity.
They are resistant to
Why?
Where have they only been observed to cause disease?
Viroids
Ribonucleases
They don’t fit into ribozymes
Plants
This type of virus like particle requires a helper virus for its replication, and carries its own capsid protein gene
What are the examples given in lecture
Satellite Viruses
Hepatitis D, HDV
These virus like particle require a helper virus for replication BUT require the capsid protein from the helper virus
Satellite RNAs
These are proteinaceous infectious particles that lead to transmissible spongiform encephalopathies, like mad cow disease
Prions
What makes prions particularly dangerous in Mad Cow and ground beef?
Heating denatures DNA and RNA but not protein structures
What does prion do to proteins?
What symptoms show in mad cow?
If its note caught before slaughtering, the disease spreads.
Also deer in WI and MI have prions
Cause the proteins to form a prion shape, leading to death of neurons
holes in brain, sponge like
Note: spontaneous prion diseases have formed, though very rare, possibly because of
genetic mutation
