Structure and chemical composition

Question 1

smallest virus

Answer 1

porcine circovirus

Question 2

largest animal/humans/birds

Answer 2

poxvirus

Question 3

shapes
ebola
rabies
bacteriophage
tobacco mosaic
poxvirus
rotavirus

Answer 3

filament shaped
bullet shaped
tadpole
rod shaped
brick shaped
spherical

Question 4

pleomorphism

Answer 4

ability of virus to alter their shape or size due to presence of lipid envelope

Question 5

methods for determining morphology of virus
EM
Cryo-EM
X ray crystallographic method
NMR

Answer 5

electron microscopy
cryo electron microscopy (freeze virus with liquid N)
crystallize viral protein –> put xray –> generate computer image
nuclear magnetic resonance - uses electromagnetic radiation

Question 6

DNA/RNA gene surrounded by…

Answer 6

capsid (protein coat)
sometimes lipid envelope

Question 7

capsid

Answer 7

protein shell of virus that encases nucleic acid
made up of capsomeres
most viruses have 1 capsid but reoviruses have double layered capsid

Question 8

capsomere

Answer 8

basic subunit protein in the capsid of a virus

Question 9

nucleocapsid

Answer 9

capsid + nucleic acid

Question 10

helical symmetry

Answer 10

capsomere and nucleic acid wound together in helical tube
MUST be enclosed within a lipoprotein envelope
-naked helicocapsid has no envelope

Question 11

icosahedral symmetry

Answer 11

two types of capsomeres present
pentagonal capsomeres and hexagonal capsomeres
always 12 pentons, hexons varies
triangulation number: relation between numb of pentagons and hexagons
can be naked or enveloped

Question 12

triangulation number formula

Answer 12

T = h^2 + h x k + k^2
h and k are distances between successive pentagons on virus surface

Question 13

parvovirus capsid symmetry

Answer 13

T = 1, simplest

Question 14

reoviridae symmetry

Answer 14

outer capside has T = 13 and inner is T = 2 –> 2 CAPSIDS

Question 15

complex symetry

Answer 15

pox virus

Question 16

functions of viral capsid

Answer 16

structural symmetry and protects nucleic acid from enzymes, chemicals and physical conditions

Question 17

receptor attachment proteins on capsid facilitate (5):

Answer 17

1. attachment of virus to receptors on host
2. interact with host cell memb. to form envelope
3. uncoat of genome in host cell
4. transport viral genome to appropriate site
5. recognition and packaging of nucleic acid genome

Question 18

capsid contains ?

Answer 18

antigenic sites – determine antigenicity of virus

Question 19

enveloped viruses have

Answer 19

lipid bilayer with embedded proteins

Question 20

how is viral envelope acquired?

Answer 20

budding of viral nucleocapsid through cellular membrane, cytoplasmic membrane, golgi membrane or nucleus membrane of the host

Question 21

2 proteins found in envelope

Answer 21

glycoprotein
matrix protein

Question 22

envelope glycoproteins (2 types)

Answer 22

1. external glycoprotein: major antigen of the virus and involved in hemagglutination, receptor binding, antigenicity and membrane fusion
2. channel proteins: mostly hydrophobic proteins that form a protein lined channel through the envelope –> alter permeability of the membrane and important in modifying internal envi. of virus

Question 23

envelope matrix protein

Answer 23

link internal nucleocapsid to lipid membrane envelope
play crucial role in virus assembly
stabilize lipid envelope

Question 24

matrix protein serves as…

Answer 24

recognition site of nucleocapsid at plasma membrane and mediates encapsidation of RNA nucleoprotein cores into the membrane envelope

Question 25

lipid bi layer in virus envelope acquired from:
is it sensitive to heat?
enveloped virus easy to sterilize?

Answer 25

cell membrane of host cell
yes, very sensitive to pH change, heat, etc
can be inactivated by dissolving lipid membrane with ether, chloroform, detergent, sodium deoxycholate
YES, cannot survive in envi. for long period of time and easier to kill than non enveloped virus

Question 26

virus nucleic acids can be: (2)

Answer 26

DNA or RNA, both can be DS or SS

Question 27

viral DNA can be in what 2 shapes

Answer 27

linear and circular

Question 28

+ sense strand vs. - sense

Answer 28

+ sense: 5’-3’ and translated into protein
- sense: 3’-5’ and must be converted to +RNA before becoming protein

Question 29

genetic diversity due to :

Answer 29

antigenic drift which causes mutations

Question 30

mechanisms of antigenic shift (2)

Answer 30

1. recombination: exchange of NT sequences, only involves 1 gene segment
2. reassortment: mix and match of both virus, only possible with more than 1 gene segment

Question 31

Viral enzymes (3)

Answer 31

1. nucleic acid polymerase: viral genome replication
2. reverse transcriptase: generates DNA from RNA
3. retroviral integrase: inserts viral DNA into host for replication

Question 32

viral nonstructural proteins

Answer 32

appears when virus is replicating, occurs only INSIDE the host cell, allows viral rep to happen and prevents host cell from disrupting viral rep

Question 33

incomplete virion

Answer 33

capsid with no DNA/RNA (empty egg shell)

Question 34

defective virions

Answer 34

virus lacks complete copy of viral genome due to mutations/error so virus cant replicate by itself

Question 35

pseudovirion

Answer 35

contains nonviral genome within the viral capsid, such as host nucleic acid instead of viral nucleic acid