35 Viral Structure

Question 1

well-studied viruses are mostly what?

Answer 1

animal pathogens

Question 2

3 virus facts to review, not memorize

Answer 2

• Viruses influenced evolution
• viruses are majority of biomass in oceans
• viruses are small, and all have a capsid

Question 3

viruses are classified by? (4)

Answer 3

• morphology
• genome structure
• replication style
• disease

Question 4

outside a cell a virus is called a?

Answer 4

virion, and has a protein shell (some also a lipid membrane and/or enzymes)

Question 5

Inside a cell, a virus technically consists of?

Answer 5

-genome, RNA, and proteins encoded for in its genome

Question 6

Viral replication time period is defined by ???

Answer 6

eclipse period

Question 7

T/F Tougher viruses have envelopes?

Answer 7

false. the additional lipid envelope around their capsid makes them weaker.

Question 8

virus lipid envelopes interact w/ host how?

Answer 8

glycoproteins

Question 9

simple icosahedral has how many sides, with how many axis of symmetry?

Answer 9

-20
-2,3, and 5 axis
[no virus is this simple though]

Question 10

if a virus is not icosahedral and not complex, it must be..

Answer 10

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]

Question 11

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?

Answer 11

163

Question 12

T/F all human helical viruses are enveloped? What are 3 examples?

Answer 12

T

-ebola, paramyxovirus, vesicular stomatitis

Question 13

What is our example of a complex virus?

Answer 13

poxvirus [also is an exception because it is the only DNA virus that doesn’t replicate in the nucleus!]

Question 14

Viruses are how many nm?

Answer 14

30-200 nm

Question 15

Viruses are linear or circular? Single piece or multiple pieces? Can contain more than one type of genome (dsRNA, etc)?

Answer 15

• Both.
• Both.
• False, only 1.

Question 16

what type of genome? Herpesvirus

Answer 16

dsDNA linear nonsegmented

Question 17

what type of genome? Papillomavirus

Answer 17

dsDNA circular nonsegmented

Question 18

what type of genome? retrovirus

Answer 18

ssRNA (linear nonsegmented)

Question 19

what type of genome? rotavirus?

Answer 19

dsRNA (linear segmented)

Question 20

I am a negative strand RNA virus. I enter the cell. What is my first 3 steps?

Answer 20

• Make (+) sense RNA
• Make protein (which then can make copies of its genome)
• Protein makes both (-) and (+) strand RNA copies

Question 21

What blocks attachment of a virus to a cell?

Answer 21

antibodies

Question 22

What’s a VAP? What’s a special example?

Answer 22

• virus attachment protein that binds to cell surface receptors for internalization.
• Some are hidden down in canyons to avoid antibodies (poliovirus!)

Question 23

VAPs only bind proteins? T/F

Answer 23

F.

Question 24

What gives VAP’s tropism?

Answer 24

receptors are only on certain cells, and the VAP recognizes only 1 or a few receptors.

Question 25

T/F enveloped viruses have VAPs too?

Answer 25

T, it is their glycoprotein attached to the envelope.

Question 26

What’s unique about adenovirus?

Answer 26

protruding knobs interact w/ host receptors

Question 27

Non-enveloped viruses enter cells how? (2)

Answer 27

• 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.

Question 28

Enveloped viruses enter cells how?

Answer 28

• 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.

Question 29

just like naked viruses, what enveloped viruses require endosome low pH

Answer 29

measles, influenza, west nile

Question 30

How does a virus un-coat?

Answer 30

“loosens” the capsid. Goes to site of replication.

Question 31

T/F humans have RNA dependent DNA polymerase?

Answer 31

T, in telomerase.

Question 32

T/F some viruses carry their own DNA-dependent DNA polymerase? How about RNA-dependent DNA polymerase? Some viruses make their own proteins?

Answer 32

T
T
F

Question 33

T/F all RNA viruses replicate in cytoplasm?

Answer 33

F, influenza is the exception.

Question 34

What are the first 2 steps for a retrovirus with RNA?

Answer 34

• 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…

Question 35

A retrovirus inside a host’s genome is called?

Answer 35

provirus

Question 36

T/F? In general RNA viruses encode their own polymerases?

Answer 36

T [DNA viruses in general don’t]

Question 37

Which viruses have error-prone polymerases?

Answer 37

RNA & retroviruses

Question 38

T/F viral capsids self-assemble before OR after insertion of the genome?

Answer 38

T

Question 39

When not lysing a cell, what machinery is used to exit the cell?

Answer 39

ESCRT

Question 40

T/F some virions in their capsids contain proteases that are chopping up their viral proteins?

Answer 40

T

[These virions are NOT YET INFECTIOUS]