Virus Replication

Question 1

Permissive Cell

Answer 1

a cell in which a virus is able to replicate

Question 2

Non-Permissive Cell

Answer 2

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

Question 3

Multiplicity of Infection

Answer 3

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

Question 4

Latent period of viral growth curve

Answer 4

after uncoating and till just before the 1st apparence of extracellular NEW virus particles

Question 5

Eclipse Period of viral growth curve

Answer 5

after uncoating and till just before 1st appearence of intracellular NEW virus particle

Question 6

Burst size

Answer 6

of infectious virions released per average cell

Question 7

T/F:

Each virus has its own specfic receptor or receptors on specific host cells.

Answer 7

True.

Virus attachment to receptors on host cells are very specific.

Some cases a co-receptor is required.

Some viruses may use more than one host cell receptor (HIV).

Question 8

Methods of viral penetration (four)

Answer 8

1. receptor mediated endocytosis (non-enveloped and enveloped)
2. pore mediated penetration (non-enveloped)
3. surface membrane fusion (enveloped)
4. anti-body mediated attachment and penetration (uncommon)

Question 9

Method of receptor mediated endocytosis of non-enveloped virus.

Answer 9

1. binds to receptors
2. vesicle formation
3. endsome formation
4. endosome pH drops altering the capsid of the virus resulting in the release of virus into cytoplasm
5. enzymes break down capsid realing viral nucleric acid

Question 10

Method of pore mediated penetration

Answer 10

1. virus attaches to host cell membrane
2. forms a pore in the membrane
3. injects nucleric acids

Question 11

Method of surface membrane fusion

Answer 11

1. virus binds to the receptors on host cells membrane
2. envelope binds to and remains apart of the cell membrane
3. virus is released into the cytoplasm

Question 12

Method of receptor mediated endocytosis of enveloped viruses

Answer 12

1. binds to receptors
2. vesicle formation
3. endsome formation
4. endosome pH drops altering the enevlope of the virus resulting in the fusion of the viral envelope to the endosome
5. virus is released into cytoplasm
6. enzymes break down capsid realing viral nucleric acid

Question 13

Which one of the following methods cannot be used by viruses for penetrating into the host cell?

A. receptor mediated endocytosis

B. membrane fusion

C. pore-mediated penetration

D. exocytosis

Answer 13

D. exocytosis

Question 14

T/F:

The infectivity of virions are lost after uncoating.

Answer 14

True

Question 15

What is the function of reverse transciptase?

Answer 15

to convert viral RNA to cDNA during virus replication

Question 16

What are the modifications occuring during processing of primary RNA transcript / Pre-RNA

Answer 16

1. capping - adittion of 7-methygluanosine to the 5’ end of RNA
2. addition of polyA tail - to 3’ end of RNA
3. splicing - removing introns and joing exons in primary transcript

Question 17

T/F:

The polyA tail is added to the 3’ end of viral mRNA.

Answer 17

True.

Question 18

T/F:

Assembly and maturation of new viruses can ONLY take place in the cytoplasm.

Answer 18

False.

May take place in the nucleus, cytoplasm or plasma / cell membrane.

Question 19

T/F:

New naked virions are released from host cell by budding while new enveloped virions are released from host cell by lysis of the host cell.

Answer 19

False.

New naked virions are released from host cell by lysis of the host cell while new enveloped virions are released from host cell budding.