Viral Structure

Question 1

what is a Capsid?

Answer 1

Viral container or shell proteins

Question 2

what is a Nucleocapsid?

Answer 2

Situation where the capsid also contains the genome

Question 3

what is an Envelope?

Answer 3

host derived lipid bilayer membranes enclosing nucleocapsids

Question 4

do all viruses have an envelope and a capsid?

Answer 4

no

Question 5

virion must be both —-

Answer 5

stable (outside cell) and unstable (within the cell), depending on stage of infectious cycle

Question 6

How can you study viral structure?

Answer 6

1. electron microscopy
2. cryo-electro microscopy
3. X-ray crystallography
4. Nuclear Magnetic Resonance Spectroscopy (NMR)

Question 7

how does e- microscopy work? disadv?

Answer 7

negative staining: stain samples with e- dense materials so e- is absorbed, but this might destroy ultrastructural features

Question 8

how does Cryo- Electron Microscopy work?

Answer 8

• NO STAIN; structure preservation
• Flash freeze samples and image at very cold temperatures
• The freezing is the contrast. Aims to preserve structures.
• Use of computers to reconstruct images (3D reconstruction)

Question 9

How does X-ray crystallography work?

Answer 9

must have ability of viral protein/virion to crystallize

has canyons (interact with host cell receptors) in 3D structure

Question 10

How does Nuclear Magnetic Resonance Spectroscopy (NMR) work?

Answer 10

if protein doesn’t crystallize:
- Radiation emitted from a nucleus in a magnetic field
- Radiation emitted are measured by spectra
- Inherent property of certain nuclei to have a magnetic moment

SINGLE PROTEINS SEEN

Question 11

how do the viral structural techniques compare in resolution?

Answer 11

X-Ray and NMR > Cryo- Electron EM > Electron Microscopy

Question 12

how is NMR different from the viral structural biology techniques?

Answer 12

Cry- Electron EM , Electron Microscopy and X-Ray give full virion structures and NMR will only give viral proteins

Question 13

virions are made of many copies of a

Answer 13

FEW PROTEINS (The viral genome’s coding capacity is limited)

Question 14

why is protein subunits few and symmetrical?

Answer 14

If protein subunits on the surface are identical, then the contacts will be identical generating a symmetrical object

Question 15

what are the two types of symmetry for viral proteins?

Answer 15

Helical symmetry:
- rod-shaped viruses
Polyhedral symmetry:
- round viruses

Question 16

Rules of viral symmetry Provide the basis for —

Answer 16

assembly

Question 17

what are the rules of viral symmetry?

Answer 17

1. Each subunits had identical bonding contacts with neighbouring subunits
2. Bonds between subunits are mostly via non-covalent interactions

Question 18

why are bonds non-covalent?

Answer 18

need to break apart bonds to interact with host

Question 19

how is viral symmetry used in vaccines?

Answer 19

(Self)-Assembly of coat proteins for Hepatitis B Virus and Human Papilloma

(Virus into Virus-Like Particles bc shell can give immune response)

Non-infectious but immunogenic and made in yeast! No Nucleic Acid

Question 20

examples of helical symmetry>

Answer 20

1. measle virus
2. vesicular stomtits virus
3. ebola virus

Question 21

how does viral helical symmetry work?

Answer 21

protein subunt in nucleocapsid interact with an identical protein subunit in an identical manner and interact with viral genome. protein subunts can be 1+ protein types

Question 22

viral helical symmetry in ebola virus?

Answer 22

• nucleoprotein directly surrounds the viral genome
• nucleoprotein is surrounded by viral protein making nucleocapsid

Question 23

what was a discovery of round/spherical capsids?

Answer 23

Round capsids have a defined number of proteins in multiples of 60

Question 24

what type of symmetry does a round capsid have?

Answer 24

icosahedral symmetry (20 triangle faces)
- 5-fold on vertice
- 2-fold edge
- 3-fold face

Question 25

exception to round capsid axis of symmetry?

Answer 25

norwalk virus (larger virus)
Quasiequivalent

Question 26

how does polivirus show round capsid symmetry?

Answer 26

3 viral proteins folded by protein (3CDpro) cutting extra strands so VPs arrange in each triangle face of sphere

Question 27

where do viral envelops derive from?

Answer 27

host (after virion replication in host) by taking membrane from infected cell by BUDDING NUCLEOCAPSID

Question 28

what is the envelope of virus made of? where does it come from?

Answer 28

use host machinery to make viral envelope gyloproteins that wait at host cell surface so that virion can pick them up as they leave the host membrane (lipid bilayer from host surrounds virus)