Lec 2: Structure

Question 1

Viral components: (3)

Answer 1

1. ) nucleic acids
2. ) capsid
3. ) envelope (if enveloped)

Question 2

(+)RNA –>

(-)RNA –>

Answer 2

(+)RNA –> can be directly used to synthesize protein

-)RNA –> compliment to (+

Question 3

viroid =

Answer 3

small, self-replicating ss circular RNA molecule w/o protein coat

Question 4

viroids are the smallest

Answer 4

infectious pathogens known

Question 5

ALL known viroids…

Answer 5

infect higher plants

Question 6

viroids often transmitted (2)

Answer 6

mechanically

& through pollen and seed

Question 7

genome is packages in a protein structure known as a

Answer 7

capsid

Question 8

many viruses also have a

which…

Answer 8

lipid component
which are generally present @ the surface of the virion forming an envelope (which also contains proteins with roles in aiding entry into host cells)

Question 9

a few viruses form

Answer 9

protective protein occlusion bodies around their virions

Question 10

Function of Viral Capsids: (2)

Answer 10

1. ) protect viral genome

2. ) aid in entry of virus to a host cell

Question 11

Naked virus structure:

Answer 11

capsid + genome = virion

Question 12

Other viruses structure:

nucleocapsid =

Answer 12

(outer layer protein sometimes) + lipid envelope + capsid + genome = virion
nucleocapsid = capsid + genome

Question 13

5 types of viral structure:

Answer 13

Icosahedral
Enveloped Icosahedral
Helical 
Enveloped Helical
Complex

Question 14

Virus genomes: (7)

*note:

Answer 14

ss, linear DNA
ds, linear DNA
ss, circular DNA
ds, circular DNA

ss, linear RNA
ds, linear RNA
ss, circular RNA

*note: NO ds circular RNA viral genome discovereed yet

Question 15

How are virus genomes packed?

• Some viruses:
• Many viruses:
• Some capsid proteins:

Answer 15

• Some viruses: capsid protein coats the genome
• Many viruses: nucleic acids bind inner part of capsid protein non-covalently (anchors DNA/RNA w/in capsid to avoid free-floating)
• Some capsid proteins: have regions such as zinc finger that binds to nucleic acids

Question 16

Human genomes =

Viral genomes =

Answer 16

chromosomes

segmented

Question 17

most viruses consist of

but some…

Answer 17

a single molecule of nucleic acid

…but some have genes encoded in 2 or more nucleic acid molecules = segmented

Question 18

segmented genomes are more common in

Answer 18

RNA viruses than DNA ones

Question 19

some viruses package genome segments into…

while others package genome segments into…

Answer 19

one virion  (ex: influenza virus)
separate virions  (ex: brome mosaic virus)

Question 20

Brome Mosaic Virus contains…

Answer 20

3 types of particles that are physically & virtually indistinguishable:

1. ) most dense (RNA1)
2. ) least dense (RNA2)
3. ) middle density (RNA3 & RNA4)

Question 21

Why is segmentation favorable? (3)

but…

Answer 21

1.) allows virus to survive environmental pressure
2.) more potential for gene recombination
3.) faster evolution
…but for those who package genome into separate virion, at least one of each has to infect the same cell

Question 22

(Capsid proteins)
Simple Virus =
Complex Virus =

Answer 22

= 1 protein type for capsid

= multiple protein types for capsid

Question 23

capsid proteins are…

Answer 23

asymmetrical, but are organized to form symmetrical structures

Question 24

many _____ viruses have helical symmetry

Answer 24

ssRNA

Question 25

Helical symmetry:

Answer 25

RNA is coiled in the form of a helix and many copies of the same protein species are arranged around the coil forming an elongated structure

Question 26

helically symmetrical viruses can have rigid or flexible rods depending on

Answer 26

if strong or weak bonds are present between the protein molecules

Question 27

the length of the capsid is determined by

Answer 27

the length of the nucleic acid

Question 28

the symmetry of a capsid is based on

Answer 28

how you look @ it

Question 29

to construct icosahedrons, you need

Answer 29

different types of proteins

Question 30

to modify icosahedrons, you need

Answer 30

to add more proteins

Question 31

when constructing icosahedrons... | so...

Answer 31

it is impossible for all molecules to be arranged perfectly symmetrically with equivalent bonds, ...so there is the Quasi-Equivalence Theory

Question 32

Quasi-Equivalence Theory

Answer 32

the molecules of an icosahedron don't interact exactly equivalently with e/o, but NEARLY equivalently

Question 33

General Bacteriophage Structure:

Answer 33

Icosahedral Head: stores DNA Tail: transfers DNA Tail Fibers: distinguish which bacteria is the host

Question 34

all tailed bacteriophages have _____ genome type

Answer 34

dsDNA

Question 35

many viruses have a _____ ________ component

Answer 35

lipid membrane component

Question 36

virus lipid membrane is typically associated with

Answer 36

virus protein

Question 37

virus lipid membrane + virus protein = ________, which....

Answer 37

envelope, which encloses the nucleocapsid (nucleic acid + capsid)

Question 38

most viruses get their membrane from _____, and this makes them some viruses get their membrane from _____, and this makes them

Answer 38

budding out of cells = external | assembly step = internal

Question 39

virus membranes can be either

Answer 39

internal or external on the virion

Question 40

many animal viruses are

Answer 40

enveloped

Question 41

most of the proteins associated with the membranes of enveloped viruses are

Answer 41

integral membrane proteins

Question 42

most virion membranes are derived from

Answer 42

host cell membranes that undergo modification before incorporation into virions

Question 43

some viruses are able to replicate in

Answer 43

more than one kind of host

Question 44

progeny virions are released from cells; the lipid composition of the envelope may

Answer 44

reflect that of the host cell

Question 45

envelopes are obtained by

Answer 45

budding through a cellular membrane (except poxviruses)

Question 46

envelopes allow the possibility of

Answer 46

exiting the cell w/o killing it

Question 47

envelopes contain at least one

Answer 47

virally coded protein (for host attachment)

Question 48

loss of envelope =

Answer 48

loss of surface protein = loss/reduction of infectivity

Question 49

(envelope glycoproteins) are = function = found =

Answer 49

``` are = proteins modified by attachment to a sugar function = recognition found = on cell surface (firmly embedded in the envelope bilayer) ```

Question 50

envelope glycoproteins are firmly embedded

Answer 50

in the envelope bilayer

Question 51

envelope glycoproteins can form... | used for...

Answer 51

spikes or other structures on the outside of the virion used for attachment to host cell

Question 52

enveloped viruses are susceptible to

Answer 52

acid, detergents, etc

Question 53

occlusion bodies mostly found in

Answer 53

insect cell viruses

Question 54

occlusion bodies =

Answer 54

crystalline protein matrix (extra layer of protection) surrounding the nucleocapsid

Question 55

occlusion bodies are produced in the

Answer 55

nucleus or cytoplasm of infected cells

Question 56

occlusion bodies confer

Answer 56

resistance to adverse environmental conditions on the virus

Question 57

occlusion bodies are dissolved by

Answer 57

the alkaline pH of the insect gut, resulting in the release of infectious virus particles

Question 58

virus genome can only be... | but virions can have...

Answer 58

one type | different types of nucleic acids to help in replication

Question 59

DNA viruses contain... | & function...

Answer 59

``` virus RNA (short RNA sequences covalently attached to DNA) & function as primers for DNA synth & remain attached to the genome in the mature virion ```

Question 60

other cell molecules incorporated into virions:

Answer 60

tRNA proteins polyamines cations

Question 61

polyamines & cations function in virions =

Answer 61

neutralize the negative charges on the virus genome