Chapter 8 Assembly and exit of visions from the cell

Question 1

1. How are virions of ssRNA viruses with helical structure (such as tomato mosaic virus) assembled?
2. Do ssRNA helical viruses have more than one protein species associated with their nucleocapsids?

Answer 1

1. it involves coating the genome and its copies with multiple copes of a protein
   
   1. coat protein for tobacco mosaic protein or nucleoprotein for infuenza
   2. genome becomes the scaffold for teh nucleocapsids assembly
2. ?? im leaning towards no
   
   1. (-) RNA genomes becomes associated with additional proteins

Check this slide

Question 2

1. How does genome of icosahedral viruses like herpes and tailed pages get packaged in the virion?
2. what enzymes and proteins are involved?

Answer 2

1. When their is an accumulation of threshold amount of virion components the procapisd construction occurs.
   
   1. the procapisd or proceed in the case of bacteriophage
   2. the pro capsid is filled with he virus genome
      
      1. genome enters through a channel located at one of the 12 vertices
      2. portal contains powerful motor that moves DNA into procapsi
   3. prolapsed undergoes modification to form the mature capsid
      
      1. changes from spherical to icosahedral shape
         
         1. caused by cleavage of one ore more structural proteins
2. terminase on the end of the viral genome concatamere grabs onto and binds the prolapsed portal proteins and enters the capsid with help of ATP. The concatmere is then cleaved and packaging is complete
3. packaging enzymes , motor proteins

Question 3

1. what is a procapsid?

Answer 3

empty protein shell that undergoes modification to form the capsid

these are usually built around the scaffolding protein

also known as a proved in teh case of a tiled bacteriophage

Question 4

1. Why is the pressure inside a virion 10X more than that of a champagne bottle?
2. what features do the virions have to overcome this pressure?

Answer 4

1. Because the genomes are packed into small volumes so the negative charges of the genomes cause repulsion
   
   1. they are also just packed so tightly
   2. negative repulsions of the phosphate groups must be overcome
2. this can be overcome by the packaging of basic protein, which are postively charged along with the genome
3. overcome by:
   
   1. positively charged molecules like polyamides and cations
   2. basic VP (structural proteins) (+)
   3. cell histones

Question 5

1. why pressure 10X more
2. what features do virions have to overcome this pressure?

Answer 5

1. pressure 10 more because they are genomes are tightly packed in a small volume and the negative charges of the phosphate group repell
2. packaging with basic positively charged proteins
   
   1. vp basic structural proteins , histones, polyamides and cations
   2. look at the picture

Question 6

1. How are virus nucleic acids selected for packaging in the vision over cell nucleic acids

Answer 6

1. recognition by a virus protein of a specific sauce, known as packaging signal
   
   1. in ss genomes the packaging signal is in region of teh secondary structure
2. Structural proteins VP recognizes specific genome sequences

Question 7

1. What are the steps in directed assembly of herpes simple x virions?

Answer 7

procapside contains scaffolding proteins that are temporarily present while teh virion is under construction. Once their job is complete, they are removed from the prolapsed. some removed by proteolysis and others are removed by intact and can be recycled.

look at the slide 11 for explanation

Question 8

1. What is scaffolding protein?

Answer 8

1. scaffolding protein = proteins that are temporarily present while the virion is under construction but are not present in teh mature version

Scaffolding proteins of the tailed phages play roles in determining the size and shape of the phage head.

Question 9

1. what happens after scaffolding proteins after they have served their role

Answer 9

1. recycled or removed form teh procapis

Question 10

1. Steps in virus-budding from non-plasma membrane?
2. use herpes as and example
3. where does the virion acquire its trans-membrane proteins from?

Answer 10

1. picture
2. .
3. Virion squires its transmebrnae proteins from ?

Check this slide

Question 11

1. in what way are membrane regions where budding will occur modified?

Answer 11

1. the membrane region generates an insertion and accumulation of proteins (vp) like glycoproteins
2. nucleocapsids accumulate adjacent to the regions of membrane contains virus protein

Question 12

1. what are the steps in virus budding from the plasma membrane
2. where does the virion acquire its trans membrane proteins from

Answer 12

most enveloped viruses acquire their envelope by buying through the membrane of the host cell

1. STEPS
   
   1. the nucleocapsid goes to the cell membrane and the cells membrane becomes modified by the insertion of one or more species of virus proteins. Most of which are glycoproteins
   2. the nucleocapsid then buds through the membrane until it pinches off to form the virion envelope
   3. cell proteins become excluded by virus proteins
2. ??

check this slide

Question 13

1. How do virus transmembrane glycoproteins interact with nucleocapsids in vivriosn with M-proteins (matrix/membrane proteins) and virion without an M-ptrotein?

Answer 13

1. M-proteins have an affinity for membranes and bind to nucleocapsids as well as to the virus glycoproteins , which stitches the two together during budding
2. in virions without the m-protein, the surface of the nucleocapsid interacts directly with the cytoplasmic tails of the glycoproteins in the membrane
   
   1. they associate directly without the middle

Question 14

1. How are cell proteins excluded fro regions of plasma membrane where the virions will bud from?
2. are all cell membranes excluded?

Answer 14

1. The virus proteins that accumulate on teh membrane repel the cell proteins and/or the virus proteins molecules have affinities for each other
2. those regions which they have an affinity for each other may not be totally excluded and therefore may be incorporated into the virus envelopes
   
   1. ex: HIV and Major Histonecompatibilty Complex class 2 proteins (MHC 2)

Question 15

1. What is the role of endosomal sorting complex required for transport (ESCRT) in virus budding?

Answer 15

1. in the final stage of budding host cell proteins called ESCRT bind to the virus proteins and sever the membrane between teh cell and the virion.
2. ESCRT can assemble in concentric spirals constricting the neck of the vesicle until release of the vesicle occurs

Question 16

1. What is Sialic ACID (neuraminic acid)?
2. where is it found
3. how are silica acids involved with influenza virus exit from the cell?

Answer 16

1. virion enzyme of the influenza virus cleaves neuramindic acid (the substrate if the enzyme)
2. it is associated with the an envelope glycoprotein
3. when neuramindisae cleaves neurminidic acid then the virion can be released

bedded viruses stay attached to cell surfaces via HA and NA bond, the enzyme cleaves the acid from eh cell surface glycoprotein relating the virion

Question 17

1. What causes an influenza virion to be initially attache to teh outside of the cell that it buds from?
2. How does the virion free itself from this attachement?

Answer 17

1. Its attached by thee Hemaglutanin (HA) and Neuraminic Acid (silica acid) bond
2. to free itself, teh enzyme neuramindisae comes in and Cleves teh silica acid from the cell surface glycoprotein

Question 18

1. How does anti-influenza drug tamiflu work?

Answer 18

1. Tamiflu inhibits the enzyme neuraminidase. It is asialic acid analog that blocks the NA action therefore it inhibits NA so overall teh visions accumulate on teh cell surface and can no longer spread to other cells.

Question 19

1. what are mucins?
2. how do they relate to influenza infections?
3. how does influenza “deal” with mucins?

Answer 19

1. Mucins are
2. Silica acids are found in mucins

Coe back to this slide

Question 20

1. Why does influenza stay localized and vesicular stomatitis spreads to other tissues?
2. what is probably the reason for this?

Answer 20

1. Viruses bud form particular regions of the plasma membrane and if the cell is polarized then budding can take place primarily from one surface
   
   1. cells are polarized
2. influenza will bud out exclusively from the out the apical (air channel site)
3. vesicular stomates comes out the basolateral surface (inside)
4. in enveloped protein genes it was found that each protein has a signal that targets it to the surface from which the virus buds

Question 21

2. Compare and contrast the exit of bacteriophages,

viruses with enveloped derived plasma membrane,

viruses with envelope derived internal membranes and

naked viruses

Question 22

1. How do plant viruses spread from one cell to another?

Answer 22

1. viruses are Abe to spread within the host by passing from cell to cell through plasmodesmata.
   
   1. channels where plant transports materials
2. For spreading to new hosts, plant viruses leave the host cell as a component of the meal of a vector (aphid/nematode)