Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

MIMM 324 > 3. Structures of Viruses > Flashcards

3. Structures of Viruses Flashcards

1
Q

what are the 2 general functions of structural proteins in a virus?

A
  1. protect the genome
  2. deliver the genome
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what are the 3 ways that structural proteins protect the genome?

A
  1. assemble into a stable, protective protein shell
  2. specific recognition and packaging of the nucleic acid genome
  3. interact with host cell membranes to form the envelope
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what are the 4 ways that structural proteins deliver the genome?

A
  1. bind to host cell receptors
  2. uncoat the genome
  3. fuse with cell membranes
  4. transport of genome to the appropriate site in the cell
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

where does the word “capsid” come from?

A

Latin capsa = box

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

what is the capsid?

A

protein shell surrounding the genome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is a nucleocapsid?

A

a term mainly used for enveloped viruses –> nucleic acid/protein core within the virion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

why is the term nucleocapsid mainly used for enveloped viruses?

A

a non-enveloped virus is essentially the nucleocapsid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is a viral envelope?

A

lipid bilayer derived from any host membrane (golgi, lysosome, plasma membrane)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is a virion?

A

infectious viral particle

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what does it mean for a virus to be metastable?

A

have an optimal balance of STABLE and UNSTABLE states

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

describe the stable and unstable states of a virus particle

A

STABLE –> must protect the genome in the environment
UNSTABLE –> must come apart upon infection to release nucleic acid

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what are 2 things that could make a virus particle unstable?

A
  1. pH
  2. proteases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

describe the energy involved in the stability/instability of virus particle

A

Add energy during assembly
Use up the potential energy for disassembly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Are virus particles at the minimum free energy conformation? Why?

A

no –> if it was at minimum free energy, virus particle would be too stable and wouldn’t be infectious

therefore, there is some energy in the capsid to allow disassembly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

describe the stable structure of a virus particle

A

SYMMETRICAL arrangement of many identical capsid proteins to allow maximal contact –> weak individual interactions but strong sum of interactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

describe the unstable structure of a virus particle

A

virus particle can be taken apart/loosened to release the genome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

describe the interactions between capsid proteins in the stable state

A

NOT permanently bonded (i.e. not covalent), just weak interactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what are the 4 methods we use to learn about viral structure?

A
  1. electron microscopy
  2. X-ray crystallography
  3. electron cryomicroscopy (cryoEM) and tomography
  4. nuclear magnetic resonance spectroscopy (NMR)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is NMR used for?

A

less used for the capsid as a whole, more used for small single proteins

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

describe the use of electron microscopy

A

negative staining with electron-dense material but impossible to get detailed structural interpretation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the resolution of electron microscopy?

A

50-75A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

what are 2 examples of negative stains for electron microscopy?

A
  1. uranyl acetate
  2. phosphotungstate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

describe the use of Cryo-EM

A

no staining required –> freeze virus particles in water and take a bunch of images of virus on flat surface, then computer makes 3D reconstruction of virus structure

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is the resolution of cryo-EM?

A

can reach near-atomic resolution (3-5A)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
what is the gold standard method for looking at viruses?
X-ray crystallography
26
why is X-ray crystallography the gold standard for looking at viruses? what is the issue with it?
highest resolution but laborious --> not always possible for capsids/virus particles to crystallize
27
what was the first virus structure found by X-ray
tomato bushy stunt virus
28
what 2 things did Watson and Crick find about viral structure
1. capsid proteins distribute with helical symmetry for rod-shaped viruses 2. capsid proteins distribute with platonic polyhedra symmetry for round viruses
29
what are the 3 parts of a capsid
1. SUBUNIT 2. PROTOMER 3. CAPSOMERE
30
what is a capsid subunit?
single folded capsid protein
31
what is a capsid protomer?
asymmetrical, structural unit --> minimal unit from which capsids/nucleocapsids are assembled
32
what is a capsomere?
assembled from protomers --> pentamers and hexamers
33
describe the assembly of viruses
capsid proteins SELF ASSEMBLE into VIRUS LIKE PARTICLES
34
what are virus like particles used for?
vaccines!
35
describe the HPV vaccine
L1 capsid proteins are expressed in yeast to make HPV virus like particles which presents to the immune system as the virus
36
what are the 2 rules of viral self-assembly?
1. each subunit makes identical contacts with its neighbours 2. the binding contacts are NON-COVALENT and WEAK
37
why can viruses self-assemble into a symmetric arrangement?
there are repeated interactions of chemically complementary surfaces at the subunit interfaces which naturally lead to symmetry
38
describe the interactions between subunits
- chemically complementary (hydrophobic, +/- charge) but non-covalent and weak - reversible and meta-stable
39
why is self-assembly considered to the be error-free assembly?
very dynamic assembly of subunits --> less favourable to assemble until subunits become a pentamer, then favourable to grow
40
describe helical symmetry/assembly
1 type of coat protein engage in identical, equivalent interactions with each other AND the viral genome
41
what is the term used for a round virus?
icosahedral
42
what is the number of proteins in an icosahedral?
MULTIPLES OF 60 --> 60, 180, 240, etc.
43
what is the size of capsid proteins?
20-60 kDa
44
describe an ICOSAHEDRON - # and shape of faces - arrangement of pentamer - # of vertices to form pentamer
- 20 triangular faces - 5 triangles arrange in a pentamer - 12 vertices (i.e. center of pentamer)
45
what are the 3 types of axes of symmetry in an icosahedron? and how many of each?
- 20 three-fold axes of symmetry (1 for each triangular face) - 12 five-fold axes of symmetry (1 for each vertex, center of pentamer) - 30 two-fold axes of symmetry (1 for each edge)
46
what is the minimal number of subunits in an icosahedron?
60 identical subunits with 3 per triangular face
47
interactions of all subunit molecules with their neighbours are ________ / _______
interactions of all subunit molecules with their neighbours are IDENTICAL / QUASIEQUIVALENT (head-to-head, tail-to-tail)
48
what is an example of an icosahedron virus with T=1?
adeno-associated virus 2 (parvovirus)
49
how are larger icosahedrons built?
add HEXAMERS!!!!
50
how do you calculate the number of pentamers and hexamers in an icosahedron?
capsid of 60*T subunits: - 12 pentamers (always 12) - 10(T-1) hexamers
51
what does T stand for? what is it a measure of?
triangulation number --> a measure of capsid size
52
compare the shape of pentamers and hexamers
pentamers are more curved, hexamers are more flat
53
when you add hexamers to an icosahedron, is it still an icosahedron?
NO!! but maintains icosahedral symmetry
54
describe the number of subunits, pentamers, and hexamers in a capsid with T = 3
60*T = 60*3 = 180 subunits 12 pentamers 10(T-1) = 10(3-1) = 20 hexamers
55
what is quasiequivalence?
when a capsid contains more than 60 subunits (T>1), each subunit has a quasiequivalent position
56
if subunits arrange as pentamers and hexamers, how can they be quasiequivalent if diff shapes?
hexamers are not much different from pentamers, so each subunit experiences a similar environment in each shape and are arranged similarly BUT non-covalent properties are not exactly identical
57
the triangulation number is the number of _________ what does this indicate about T=1 virus? T=4 virus?
the triangulation number is the number of structural units in each triangular face of an icosahedron T=1 virus --> each triangular face contains 1 structural unit T=4 virus --> each triangular face contains 4 structural units
58
describe large complex capsids
large complex capsids have distinct components with different symmetries proteins have specialized roles
59
what does adenovirus have on each of its vertices?
adenovirus has fibers at each of its 12 vertices
60
describe the capsid of tailed bacteriophages
HEAD = icosahedral capsid contractile TAIL = helical capsid attached to head
61
what is the function of the baseplate of tailed bacteriophages?
for attachment
62
how do enveloped viruses acquire its envelope?
budding of nucleocapsid thru cellular membrane
63
what type of symmetry can nucleocapsids have inside the envelope?
helical or icosahedral symmetry
64
describe the 2 steps of viral budding
1. viral capsid assemble close to budding site 2. virus undergoes budding where viral glycoproteins are on the surface
65
what are viral envelope glycoproteins?
integral membrane proteins modified with sugars
66
what are the 2 domains of viral envelope glycoproteins? describe their roles
1. ectodomain --> attachment, antigenic sites, fusion 2. internal domain --> assembly
67
what are spike proteins?
oligomeric glycoproteins
68
what are 3 additional virion components in the capsid?
1. enzymes 2. transcription activators 3. cellular components
69
what are 4 enzymes found in the virion?
polymerases, integrases, associated proteins, proteases
70
why are transcriptional activators required in a virion?
for efficient infection
71
what are some examples of cellular components found in a virus?
histones, tRNAs, lipids, host proteins
72
why might viruses have histones?
viral dsDNA wrapped around cellular histone
73
are all cellular components in a virus helpful?
no! virus may just be sloppy and take up things

MIMM 324 (37 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions