Virus replication

Question 1

process of viral rep requires ?

Answer 1

assembly line

Question 2

permissive cell

Answer 2

cell in which virus is able to replicate; cell machinery supports replication of the virus

Question 3

non permissive cell
+ 2 types

Answer 3

factors necessary to viral reproduction are not present
1. virus cant enter/attach/infect
2. virus gets in but conditions dont support reproducing

Question 4

Multiplicity of infection MOI

Answer 4

number of virions that are added per cell during infection

Question 5

eclipse period

Answer 5

after uncoating until we see the first virus intracellularly

Question 6

latent period

Answer 6

uncoating to newly formed virus particle extracellulary

Question 7

One step virus growth curve (3 phases)

Answer 7

1. adsorption: virus attaches and enters cell, titer of free virus in the medium may decline
2. eclipse period: time between uncoating and appearance intracellularly of first virion
3. latent period: time before new virus appears in the medium – no extracellular virions are detected

Question 8

burst size

Answer 8

number of infected virions released per average cell

Question 9

steps of viral replication

Answer 9

attachment - penetration - uncoating - synethesis of viral nucleic acid and capsid - assembly and maturation - release in large numbers

Question 10

Viral attachment

Answer 10

-very specific, like lock and key
-each virus has its own receptor on specific host cells
-mediated by interaction between virus and complimentary receptor on host cell (if cell lacks receptor = was not infected by virus)
-some cases: binding to cellular receptor is not sufficient for infection: additional surface molecule (co receptor) must be added

Question 11

what virus uses more than one host cell receptor to enter?

Answer 11

HIV

Question 12

co receptor

Answer 12

binding to cellular receptor is not sufficient for infection, additional cell surface molecule is required for entry because it strengthens bond between host cell and viral cell

Question 13

virus penetration and uncoating: nonenveloped vs enveloped viruses
other methods of entry

Answer 13

nonenveloped: receptor mediated endocytosis, or pore mediated penetration
enveloped - depends on type of fusion protein which decides how enveloped virus will infect cell
- surface membrane fusion (have pH indep. fusion protein) or receptor mediated endocyt. (have pH depent. fusion protein)

other method: AB mediated attachment and penetration - FIPV

Question 14

non enveloped virus endocytosis

Answer 14

clathrin-mediated endocytosis or any other receptor mediated endocytosis of virus by host

OR

pore mediated penetration of viral genome into host cell- viruses inject genome into host cytoplasm through creation of a pore in the host membrane

Question 15

enveloped viruses

Answer 15

surface membrane fusion with pH INDEPENDENT fusion protein: fusion of virus envelope with host cell membrane occurs directly on surface of host cell

OR

receptor mediated endocytosis with pH DEPENDENT fusion protein: fusion of viral membrane with host endosomal membrane release viral genome - fusion protein needs low pH to get activated and then allows viral envelope fusion with membrane

Question 16

AB mediated attachment

Answer 16

feline infectiou peritonitis FIP virus
FIP virus enters host macrophage by attachment of its spike proteins to the CD13 receptor

Question 17

virus uncoating definition

Answer 17

release of viral genome in host cell = virion can no longer be detected

UNCOATING = loss of infectivity of virions

Question 18

viral protein and nucleic acid synthesis:
parent virus leads to what 2 outcomes

Answer 18

function 1: multiple copies for new viruses (children)
function 2: viral proteins for capsid and successful replication

Question 19

reverse transcriptase

Answer 19

conversion of viral RNA to cDNA during viral replication

Question 20

processing of primary RNA transcript (pre RNA)

Answer 20

viral mRNA must conform to requirements of host cell translation system so the host can recognize the viral mRNA and translate it

Question 21

modifications of processing primary RNA transcript/pre RNA (3)

• after processing, where are mRNAs translated

Answer 21

1. capping
2. poly A tail
3. splicing

CYTOPLASM, viral mRNA produced in the nucleus must also be exported to the cytoplasm

Question 22

Capping
Poly A tail

Answer 22

capping: Addition of 7-methylguanosine to 5’ end of RNA
Adding 3’ poly adenylated tails
Splicing: removes introns and joins exons in a primary transcript

Question 23

intron
exon

Answer 23

portion of gene that does not code for AA
portion of gene that codes for AA

Question 24

2 types of splicing

Answer 24

1. consecutive splicing: every intron is spliced out, every exon is spliced in
2. alternative splicing: all introns spliced out, only selected exons spliced in, resulting in mRNA having different coding information derived from a single gene

Question 25

2 types of viral mRNA

Answer 25

1. monocistronic = mRNA that encodes 1 polypeptide
2. polycistronic = mRNA that encodes several polypeptides

Question 26

assembly and maturation
-3 places where it could take place

Answer 26

= assembly of virus genome and proteins into new virions follow a specific order
- components packaged to form mature virions
-could take place in nucleus, cytoplasm or plasma/cell membrane (most enveloped virus)

Question 27

releasing progeny viruses (2 diff ways)

Answer 27

1. naked virions - lysis of host cell (when host cell ruptures, lets viral particles out)
2. enveloped virions - budding

naked virions cannot exit host cell by budding because they LACK an envelope

Question 28

exocytosis

Answer 28

viruses mature by budding through the membranes of the golgi, nuclear membrane or ER, vesicles containing virus then migrate to the plasma membrane and are released by exocytosis because already inside the cell

Question 29

replication of retroviruses (2 steps)

Answer 29

1. reverse transcriptase: RNA to DNA
2. integrase: integrates viral DNA into host genome

Question 30

cell to cell spread of viruses (3 types)

Answer 30

1. Extracellular spread - released viruses travel extracellularly
2. intercellular spread, viruses pass through intracellular junction between cells - results in rapid virus dissemination, evasion of immune system and persistent infections EX: HERPES
3. Nuclear spread of virus genome