Viral Replication

Question 1

permissive cell

Answer 1

a cell which a virus is able to replicate within

Question 2

non-permissive cell

Answer 2

cells in which a factor or factors necessary to viral reproduction is not present or one detrimental to viral reproduction is present

Question 3

MOI

Answer 3

number of virions that are added per cell during infection

Question 4

adsorption

Answer 4

period in which the virus attaches to and enters the cell, and the titer of free virus in the medium may actually decline

Question 5

eclipse period

Answer 5

time interval between uncoating (disappearance) and appearance, intracellularly, of first infectious progeny viruses. No infectious virus is detected during this time

Question 6

latent period

Answer 6

time before new infectious virus appears in the medium, time from uncoating to just prior to the release of the first extracellular virions

Question 7

burst size

Answer 7

number of infectious virions released per average cell

Question 8

steps of viral replication (6 steps)

Answer 8

attachement, penetration, uncoating, synthesis of viral components, assembly and maturation, release in large numbers

Question 9

attachment

Answer 9

binding of the virus to receptors on the host cell

Question 10

endocytosis

Answer 10

a process in which a substance gains entry into a cell without passing through the cell membrane

Question 11

most common form of endocytosis

Answer 11

receptor mediated endocytosis

Question 12

types of receptor mediated endocytosis

Answer 12

clathrin-mediated endocytosis of virus by host
clathrin- and caveolin-independent endocytosis
caveolin-mediated endocytosis

Question 13

how do enveloped viruses get out of the cell

Answer 13

fusion of virus membrane with host endosomal membrane releases viral genome. virus with glycoproteins bind to host membrane and fuse

Question 14

how do non-enveloped viruses get out of the cell

Answer 14

lysis

Question 15

ADCC

Answer 15

suface membrane fusion of enveloped viruses. viral glycoproteins are retained on the cell surface, and since these are antigenic, the cell can become a target of the host immune system

Question 16

pH independent fusion proteins and examples

Answer 16

receptor binding, virus with host membrane fusion, release of viron contents into host cytoplasm
ex. HIV & Measles

Question 17

pH dependent fusion proteins and examples

Answer 17

endocytosis, acidification(low pH) of endosome, HA configuration changes, membrane fusion, RNA genome enters cytosol
ex. HA in Influenza

Question 18

pore-mediated penetration

Answer 18

some non-enveloped viruses inject their genome into the host cytoplasm through creation of a pore in the host membrane

Question 19

antibody mediated attachment and penetration

Answer 19

antibodies against spike proteins of FIP cannot clear the virus from host. Rather these antibodies bind to FIP virus spike proteins and facilitate entry of viruses into host cells via antibody Fc receptor
ex. FIP- in macrophages

Question 20

uncoating within endosome (enveloped viruses)

Answer 20

low pH in endosome promotes fusion of envelope with endosomal membrane; lysis of nucleocapsid by lysosomal proteases

Question 21

uncoating at the nuclear membrane (4 ways)

Answer 21

1-pass directly through nuclear pores
2-attach to nuclear pore complex and release genome inside nucleus
3-wait for mitosis
4-genome released in nucleus and pass through pores

Question 22

poliovirus uncoating

Answer 22

not completely uncoated until inside the cell

Question 23

poxvirus uncoating

Answer 23

complex series of steps involving both host and viral gene products

Question 24

retroviruses and reoviruses replication

Answer 24

first stages of viral replication cycle occurs inside the capsid

Question 25

replication of double-stranded DNA viral genome and production of viral mRNA

Answer 25

dsDNA--> (+)RNA --> viral protein | *dsDNA for progeny viruses

Question 26

replication of single-stranded DNA viral genome and production of viral mRNA

Answer 26

(+)ssDNA --> dsDNA intermediate --> (+)RNA --> viral protein | *(+)ssDNA for progeny

Question 27

replication of double-stranded RNA viral genome and production of viral mRNA

Answer 27

dsRNA --> (+)RNA --> viral proteins | *dsRNA for progeny

Question 28

replication of single-stranded (-)RNA viral genome and production of viral mRNA

Answer 28

(-)ssRNA --> (+)RNA --> viral proteins | *(+)ssRNA intermediate --> (-)ssRNA for progeny

Question 29

replication of a single-stranded (+)RNA viral genome and production of viral mRNA

Answer 29

(+)ssRNA --> (+)RNA --> viral protein or (+)ssRNA --> (-)ssRNA --> (+)ssRNA for progeny

Question 30

replication of single-stranded (+)RNA viral genome and production of viral mRNA by way of REVERSE TRANSCRIPTASE

Answer 30

(+)ssRNA --> (-)ssDNA --> dsDNA intermediate --> (+)RNA --> viral protein or dsDNA intermediate --> (+)ssRNA for progeny

Question 31

replication of double-stranded DNA viral genome and production of viral mRNA by way of REVERSE TRANSCRIPTASE

Answer 31

dsDNA --> (+)ssRNA --> (-)ssDNA --> dsDNA --> (+)RNA --> viral protein

Question 32

mRNA cannot be recognized until it has __________ & a ____________

Answer 32

cap & a tail

Question 33

capping

Answer 33

addition of 7-methylgluanosine to the 5' end of RNA, binds to the mRNA ribosomes, mark mRNA as self

Question 34

how are caps synthesized (3ways)

Answer 34

1- synthesized by host cell enzymes (eg. Retrovirus, Adenovirus) 2- by viral enzymes (eg. Poxvirus, Reovirus) 3- cap snatching from host mRNA (eg. Influenza)

Question 35

addition of tail

Answer 35

3' poly- adenylated tail, tail interacts with poly-A binding proteins- important for translation

Question 36

3' polyadenylation

Answer 36

a stretch of adenylate residues are added to the 3' end. The poly-A tail contains ~250 A residues

Question 37

major signal for the 3' cleavage for the tail is

Answer 37

"AAUAAA" - cleavage occurs 10-35 nucleotides downstream from the specific signal sequence

Question 38

exon

Answer 38

portion of a gene that codes for AAs

Question 39

intron

Answer 39

portion of a gene that does not code for AAs or proteins

Question 40

constitutive splicing

Answer 40

every intron is spliced out and every exon is spliced in

Question 41

alternative splicing

Answer 41

all introns are spliced out and only selective exons are spliced in.

Question 42

monocistronic

Answer 42

mRNA that encodes for only one polypeptide

Question 43

polycistronic

Answer 43

mRNA that encodes for several polypeptides

Question 44

two types of polycistronic and what they yield

Answer 44

1- translation: polyprotien (multiple proteins stuck together), proteases chop them up to yield functional proteins 2- endonuclease: chops up mRNA into monocistronic mRNA, each encodes for a specific protein, they are translated into functional proteins

Question 45

viral proteins

Answer 45

enzymes, structural proteins, viral nonstructural proteins, regulatory proteins, inhibitors

Question 46

where does assembly and maturation occur

Answer 46

nucleus, cytoplasm, plasma/cell membrane

Question 47

release of progeny viruses (how in naked viruses? in enveloped?

Answer 47

naked- lysis | enveloped- budding or lysis

Question 48

layers of enveloped virus once budding occurred

Answer 48

matrix protein, host cytoplasm, virus glycoproteins

Question 49

viruses that can bud through the golgi or ER

Answer 49

flaviviruses, arteriviruses, coronaviruses and bunyaviruses

Question 50

extracellular spread of viruses

Answer 50

virus is adsorbed, enters, replicates, assembles, released and infects new host cell

Question 51

intracellular spread

Answer 51

spread from cell to cell without contact with extracellular milieu.

Question 52

mechanisms of intracellular spread

Answer 52

- cell-cell plasma-membrane fusion (Herpesvirus, Paramyxovirus and Retrovirus) - passage of virions across tight junction (Herpesvirus) - movement of virions across neural synapse (Rabies) - viral induction of actin (Poxvirus) - viral subversion of actin - membrane nanotube subversion (HIV-1) - virological synapse (Retrovirus)

Question 53

nuclear spread of virus genome

Answer 53

viral genome is integrated into the host cell genome and passed down to next progeny or generation of host cells (Retroviruses)