lecture 7

Question 1

Replication of Viruses

Answer 1

• do not have genetic capability to multiply by division
• hijacks and utilizes host cell machinery to produce its proteins and nucleic acid for next generation of virus
• process of virus replication in host cell resembles assembly line

Question 2

permissive cell

Answer 2

cell is which a virus is able to replicate

the cell machinery supports replication of the virus

Question 3

non-permissive cell

Answer 3

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

eg. absence of appropriate receptors

Question 4

MOI (multiplicity of infection)

Answer 4

refers to the number of virions that are added per cell during infection

Question 5

latent period

Answer 5

after uncoating and till just before 1st appearance and release of extracellular new virus particle

no extracellular virions detected

Question 6

eclipse period

Answer 6

after uncoating and till just before first appearance of intracellular new virus progeny particles

Question 7

adsorption

Answer 7

during this period virus attaches to and enters cell, titer of free virus in medium may decline

Question 8

burst size

Answer 8

number of infectious virions released per average cell

Question 9

virus attachment

Answer 9

• attachment to receptor/s on host cells is/are very specific, lock and key like
• each virus has its own specific receptor/receptors on specific host cells

Question 10

attachment to the host cell surface

Answer 10

• mediated by interaction between the virus and complimentary receptor on host cell surface, cell that lacks appropriate receptor escape being infected by virus
• some cases, binding to cellular receptor is not sufficient for infection, additional cell surface molecule, or co-receptor required for entry
• some viruses may use more than one host cell receptor, such as HIV

Question 11

co-receptor

Answer 11

in some cases, binding to a cellular receptor is not sufficient for infection
-additional cell surface molecule, or co-receptor is required for entry

Question 12

viruses can enter the host cell using any receptor present on surface of host cell

T/F

Answer 12

F

Question 13

penetration /uncoating of non-enveloped/naked viruses

Answer 13

1. receptor mediated endocytosis (commonly seen)

2. pore mediated penetration (in some naked viruses)

Question 14

penetration and uncoating of enveloped viruses (depends on type of fusion protein)

Answer 14

1. surface membrane fusion (have pH independent fusion protein)”
2. receptor mediated endocytosis (have pH dependent fusion protein)

Question 15

other/ uncommon methods of entry into host cell

Answer 15

-antibody- mediated attachment and penetration, as in FIPV

Question 16

Virus penetration in many non-enveloped viruses

Answer 16

-Clathrin-mediated endocytosis or receptor-mediated endocytosis of virus by host

Question 17

less common virus penetration in non-enveloped viruses

Answer 17

pore-mediated penetration of viral genome into host cell

Question 18

surface membrane fusion of enveloped viruses

Answer 18

• fusion of virus envelope with host cell membrane occurs directly on surface of host cell
• facilitated by pH independent fusion protein

Question 19

receptor mediated endocytosis of enveloped viruses

Answer 19

• pH dependent fusion protein
• fusion of virus membrane with host endosomal membrane release viral genome
• fusion protein requires low pH to be activated which is achieved in the endosome

Question 20

True/false antibody mediated attachment is used by viruses to penetrate the host cell

Answer 20

true

Question 21

virus uncoating

Answer 21

• release of viral genome into the host cell

- virion can no longer be detected

Question 22

uncoating results in…..

Answer 22

loss of infectivity of virions

Question 23

functions of the parent virus in the host cell

Answer 23

1. produce multiple copies of new viruses (children/progeny)
2. produce viral proteins for capsid and successful replication

Question 24

reverse transcriptase

Answer 24

converts viral RNA to cDNA during virus replication

Question 25

processing of primary RNA transcript (Pre-mRNA)

Answer 25

- viral mRNA must conform to requirements of host cell translation system i.e the host cell can recognize mRNA and translate - series of modification occurs known as processing of primary RNA transcript/pre-RNA - after processing mRNAs are translated into the cytoplasm - viral mRNAs produced in the nucleus must also be exported to the cytoplasm

Question 26

processing of primary RNA transcript (Pre-mRNA)

Answer 26

1. capping 2. addition of 3' poly-adenylated tails 3. splicing

Question 27

capping

Answer 27

-addition of 7-methylguanosine to the 5' end of RNA

Question 28

RNA splicing

Answer 28

process which removes introns (non-coding region) and joins exons (coding region) in primary transcript

Question 29

monocistronic mRNA

Answer 29

mRNA that encodes one polypeptide

Question 30

polycistronic mRNA

Answer 30

mRNA encodes several polypeptides

Question 31

assembly and maturation

Answer 31

- assembly of virus genome and proteins into new virions follow a specific order - all components, including nucleic acids and proteins, are packaged to form mature virions - may take place in nucleus, cytoplasm, plasma/ cell membrane (most enveloped viruses)

Question 32

naked virions release progeny by....

Answer 32

lysis of host cell (cannot exit by budding because they lack envelope)

Question 33

enveloped virions release progeny by....

Answer 33

budding through the plasma membrane

Question 34

exocytosis

Answer 34

viruses that acquire envelope while budding from ER, golgi apparatus, or nuclear/nucleus membrane leave infected host cell by exocytosis

Question 35

replication of retroviruses uses....

Answer 35

- reverse transcriptase (synthesizes RNA into DNA) | - integrase (integrates viral DNA to host genome)

Question 36

viruses can acquire the lipid envelope only from the cell membrane of infected host cells? T/F

Answer 36

F

Question 37

methods of cell-to-cell spread of viruses

Answer 37

1. extracellular spread 2. intercellular spread 3. nuclear spread of virus genome

Question 38

intercellular spread

Answer 38

results in rapid virus dissemination, evasion of immune system, and persistent infections