20 - Virus Overview (Stapleton)

Question 1

virus characteristics

Answer 1

small

obligate intracellular parasitesencased in protein package (capsid)

Question 2

adsorption phase

Answer 2

lasts 1 hour

Question 3

eclipse phase

Answer 3

10-12 hours

virus becomes uncoated

Question 4

synthetic phase

Answer 4

12 hours post infection

new virus particles are assembled and released

Question 5

latent period

Answer 5

no extracellular virus detected

Question 6

virus inside host

Answer 6

replication

consist of genome, RNA and proteins

Question 7

virus outside host

Answer 7

no replication
encased by protein shell (capsid) that interacts with environment
enveloped or not

Question 8

virus envelope

Answer 8

made of glycoproteins
derived from infected cell membrane
more sensitive to inactivation than naked viruses

Question 9

virus morphology

Answer 9

Icosahedral
helical
complex

Question 10

icosahedral

Answer 10

180-240 faces

symmetrical

Question 11

helical

Answer 11

all human helical viruses that cause diesease are enveloped

Question 12

why does viral structure matter

Answer 12

structure elicits immune response
structure imporatnat in viral replication
viral replication steps are targets of therapy

Question 13

virus genome

Answer 13

ss, ds
DNA, RNA
circular, linear
non segmented, segmented
ssRNA have polarity

Question 14

steps in replication

Answer 14

attachment
entry
uncoating
genome expression
genome replication
assembly
egress

Question 15

attachment of virus

Answer 15

using viral attachment protein (VAP), binds specific cell receptor (usually surface protein)

Question 16

non enveloped VAP

Answer 16

protein on capsid

Question 17

enveloped VAP

Answer 17

glycoprotein envelope

Question 18

naked entry

Answer 18

internalization into endosomes
neutral pH- plamsa membrane pore entry
low pH-amino acids making pore entry

Question 19

enveloped entry

Answer 19

gp VAP binds cell receptors and have hydrophobic fusion peptide
1-env membrane fuses directly with cell membrane
2-virion is internalized into endosomes

Question 20

antiviral drugs targeting entry

Answer 20

blocking entry of virus can prevent infection

Question 21

HIV attachment and entry

Answer 21

HIV gp120 attaches to CD4
conformational change to allow interacting with CCR5
exposes fusion peptide in gp41
brings viral membrane and plasma membrane together
fusion

Question 22

Influenza attachment and entry

Answer 22

influenza VAP (gp HA) interacts with cell receptor (sialic acid)
virion taken into endosomes
low pH leads to interaction between HA and endosomal membranes fusing

Question 23

DNA genome expression

Answer 23

transcription to RNA

translation to protein

Question 24

RNA+ genome expression

Answer 24

translation to protein

Question 25

RNA - genome expression

Answer 25

transcription to RNA+ | translation to protein

Question 26

retrovirus genome expression

Answer 26

RNA to DNA with reverse transcription transcription to RNA translation to protein

Question 27

genome replication by

Answer 27

DDDP DDRP RDRP RDDP

Question 28

DNA virus replicates where

Answer 28

nucleus | with DDRP

Question 29

RNA+ genome replication

Answer 29

translation to protein | transcription to RNA- to make template for RNA+

Question 30

RNA- genome replication

Answer 30

Transcription to RNA+ to make template for RNA- | Translation to protein

Question 31

retrovirus genome replication

Answer 31

RNA+ use RT to make DNA- strand and destruction of RNA+ | make DNA+ strand from DNA- template for ds DNA

Question 32

what is a provirus

Answer 32

retroviral DNA integrated into human genome

Question 33

what facilitates immune escape of viruses

Answer 33

viral polymerases are error prone | absence of proof reading activity

Question 34

translation of viral proteins

Answer 34

viruses use host ribosomes | viruses use host translation machinery

Question 35

virus assembly

Answer 35

capsid self assemble and stuff genome in (DNA, icosahedral) | capsid forms around genome (helical, some icosahedral)

Question 36

envelopment assembly

Answer 36

capsid budding into cell membrane containing viral proteins (plasma mem, intracellular mem)

Question 37

viral egress

Answer 37

cytolytic by lysing (non envelope) virus buds from plasma mem (HIV) released from secretory pathway (HCV)

Question 38

maturation in viral replication

Answer 38

proteins translated as proproteins (polyproteins) | must be processed into mature proteins and cleaved by protease to make infectious

Question 39

why do we care about replication

Answer 39

rates may correlate with pathogenesis (high rate=fulminant disease or more rapid disease) antiviral treatment that interfere with replication enzymes

Question 40

viral transmission

Answer 40

only in humans (small pox, polio, HIV) animal reservoirs but spread to humans (flu) human reservoir but no human to human transmission, through vector (dengue, yellow fever) animal or insect reservoir, rare human to human (rabies, zika)

Question 41

factors influencing acquisition of virus

Answer 41

season age genetics immune status

Question 42

enveloped virus vs. naked

Answer 42

enveloped is more sensitive to drying and must be transmitted through droplet or body fluid not as stable

Question 43

virus portal of entry

Answer 43

upper respiratory, oral, sexual | fomites, blood, zoonoses, translation, maternal to fetal