35 Viral Structure Flashcards
well-studied viruses are mostly what?
animal pathogens
3 virus facts to review, not memorize
- Viruses influenced evolution
- viruses are majority of biomass in oceans
- viruses are small, and all have a capsid
viruses are classified by? (4)
- morphology
- genome structure
- replication style
- disease
outside a cell a virus is called a?
virion, and has a protein shell (some also a lipid membrane and/or enzymes)
Inside a cell, a virus technically consists of?
-genome, RNA, and proteins encoded for in its genome
Viral replication time period is defined by ???
eclipse period
T/F Tougher viruses have envelopes?
false. the additional lipid envelope around their capsid makes them weaker.
virus lipid envelopes interact w/ host how?
glycoproteins
simple icosahedral has how many sides, with how many axis of symmetry?
-20
-2,3, and 5 axis
[no virus is this simple though]
if a virus is not icosahedral and not complex, it must be..
helix
[with constant ratio of diameter to distance covered by a full turn of helix, i.e., thicker helix covers a farther distance with each full turn]
Tobacco mosaic virus is 16.3 subunits per helix turn. How many copies of capsid protein does it need to coat 10 complete turns of its helix?
163
T/F all human helical viruses are enveloped? What are 3 examples?
T
-ebola, paramyxovirus, vesicular stomatitis
What is our example of a complex virus?
poxvirus [also is an exception because it is the only DNA virus that doesn’t replicate in the nucleus!]
Viruses are how many nm?
30-200 nm
Viruses are linear or circular? Single piece or multiple pieces? Can contain more than one type of genome (dsRNA, etc)?
- Both.
- Both.
- False, only 1.
what type of genome? Herpesvirus
dsDNA linear nonsegmented
what type of genome? Papillomavirus
dsDNA circular nonsegmented
what type of genome? retrovirus
ssRNA (linear nonsegmented)
what type of genome? rotavirus?
dsRNA (linear segmented)
I am a negative strand RNA virus. I enter the cell. What is my first 3 steps?
- Make (+) sense RNA
- Make protein (which then can make copies of its genome)
- Protein makes both (-) and (+) strand RNA copies
What blocks attachment of a virus to a cell?
antibodies
What’s a VAP? What’s a special example?
- virus attachment protein that binds to cell surface receptors for internalization.
- Some are hidden down in canyons to avoid antibodies (poliovirus!)
VAPs only bind proteins? T/F
F.
What gives VAP’s tropism?
receptors are only on certain cells, and the VAP recognizes only 1 or a few receptors.
T/F enveloped viruses have VAPs too?
T, it is their glycoprotein attached to the envelope.
What’s unique about adenovirus?
protruding knobs interact w/ host receptors
Non-enveloped viruses enter cells how? (2)
- neutral pH: receptor bind -> exposes capsid sequence that creates a pore in the cell membrane
- low pH: same deal, but they are taken into endosomes THEN generate the pore.
Enveloped viruses enter cells how?
- Glycoprotein shields from antibodies.
- Glycoprotein binds receptor
- Conformational change exposes fusion peptide, which inserts into cell membrane
- 2 alpha helix regions near the fusion peptide in the glycoprotein collapse on each other, pulling the cell toward it.
just like naked viruses, what enveloped viruses require endosome low pH
measles, influenza, west nile
How does a virus un-coat?
“loosens” the capsid. Goes to site of replication.
T/F humans have RNA dependent DNA polymerase?
T, in telomerase.
T/F some viruses carry their own DNA-dependent DNA polymerase? How about RNA-dependent DNA polymerase? Some viruses make their own proteins?
T
T
F
T/F all RNA viruses replicate in cytoplasm?
F, influenza is the exception.
What are the first 2 steps for a retrovirus with RNA?
- It has 2 copies of (+) strand RNA, so it creates…
- Copies of (-) strand DNA, and destroys the (+) strand RNA!
- Makes a (+) strand DNA to get dsDNA, and you know what happens from there…
A retrovirus inside a host’s genome is called?
provirus
T/F? In general RNA viruses encode their own polymerases?
T [DNA viruses in general don’t]
Which viruses have error-prone polymerases?
RNA & retroviruses
T/F viral capsids self-assemble before OR after insertion of the genome?
T
When not lysing a cell, what machinery is used to exit the cell?
ESCRT
T/F some virions in their capsids contain proteases that are chopping up their viral proteins?
T
[These virions are NOT YET INFECTIOUS]
