Replication

Question 1

Replication of viruses

Answer 1

Viruses do not have genetic capability to multiply by division
Virus hijacks and uses host cell machinery to produce its proteins and nucleic acid for next gen
Process of virus replication in host cell=assembly line

Question 2

Permissive cell

Answer 2

Cell in which virus is able to replicate

Cell machinery supports replication of 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 present
Absence of appropriate receptors

Question 4

MOI- multiplicity of infection

Answer 4

Refers to the number of virions that are added per cell during infections

Question 5

Latent period

Answer 5

After uncoating and til just before 1st appearance of extracellular new virus particle
Time before new infectious virus appears in the medium
During this phase no extracellular virions are detected

Question 6

Eclipse period

Answer 6

After uncoating and till just before 1st appearance of intracellular new virus particle
Time interval between uncoating (dissapearance of viruses) and appearance, intracellularly of first infectious progeny virions

Question 7

Burst size

Answer 7

Number of infectious virions released per average cell

Question 8

Steps of virus replication

Answer 8

Attachment
Penetration
Uncoating
Synthesis of viral components (nucleic acid and protein)
Assembly and Maturation
Release in large numbers

Question 9

Attachment

Answer 9

Virus attachement to receptor on host cells is very specific
Lock and key
Each virus has its own specific receptor or a few receptors on specific host cells.

Question 10

Attachment to host cell surface

Answer 10

Mediated by interactions between the virus and complimentary receptor on host cell surface
Cell that lack appropriate receptor escape from being infected
In some cases, binding to a cellular receptor is not sufficient for infection: an additional cell surface molecule, or co-receptor, is required for entry

Some viruses may use more than one host cell receptor- like HIV

Question 11

Co-receptor

Answer 11

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

Question 12

Virus penetration and uncoating in host cells- naked viruses

Answer 12

Receptor mediated endocytosis (commonly seen)

Poor mediated penetration (in some naked viruses)

Question 13

Virus penetration and uncoating in host cells- enveloped viruses

Answer 13

Depends on type of Fusion protein
Surface membrane fusion (have pH independent Fusion protein)
Receptor mediated endocytosis (have pH dependent Fusion protein)

Question 14

Virus penetration and uncoating in host cells- other methods

Answer 14

Antibody-mediated attachment and penetration

FIPV

Question 15

Clatherin mediated endocytosis

Answer 15

Or other receptor mediated
Host cell membrane form vesicle wall
pH of endosome falls and virus capsid bursts (rupture) from endosome.
Are uncoated (by enzymes) and nucleic acid released into cytoplasm

Question 16

Pore mediated penetration of viral genome

Answer 16

Non-enveloped viruses

Some inject genome into host cytoplasm through creation of a poor in the host membrane

Question 17

Surface membrane fusion

Answer 17

pH independent Fusion protein
Fusion of virus envelope with host cell membrane occurs on surface of host cell.
Facilitated by pH independent fusion protein.
capsid digested by proteolysis enzymes.
released into cytoplasm

Question 18

Receptor mediated endocytosis (pH dependent)

Answer 18

Fusion of virus membrane with host endosomal membrane release viral genome. Fusion protein requires low pH to get activated, which is achieved in endosome and thus facilitate virus envelope fusion with endosomal membrane
Fusion- not rupture!

Question 19

Antibody mediated attachment and penetration

Answer 19

Antibodies bind to virus and then can bind to host cell and allow virus inside

Question 20

Virus uncoating

Answer 20

Release of viral genome in host cell
Virion can no longer be detected
loss of infectivity of virions

Question 21

Parent virus

Answer 21

Function 1: multiple copies for new viruses

Function 2: viral proteins for capsid and successful replication

Question 22

Reverse transcriptase

Answer 22

Conversion of viral RNA to cDNA during virus replication

Question 23

Processing of primary RNA transcript

Answer 23

The viral mRNA must conform to the requirements of host cell translation system– host cell can recognize the mRNA and translate same
A series of modifications occur: capping, addition of polyA tail, splicing
After processing, mRNAs are translated in cytoplasm
Viral mRNAs produced in the nucleus must also be exported to cytoplasm

Question 24

Capping

Answer 24

Addition of 7-methylguanosine to the 5’ end of RNA

Question 25

PolyA

Answer 25

Addition of 3’ poly-adenylated tails

Question 26

Splicing

Answer 26

RNA splicing is a process that removes introns and joins exons in a primary transcript

Question 27

Types of viral mRNA

Answer 27

Monocistronic: mRNA that encodes one polypeptide
Polycistronic: mRNA that encodes several polypeptides

Question 28

Polycistronic mRNA

Answer 28

translation to polyprotein and protease to functional proteins
OR
endonuclease to monocistronic mRNAs then translation to functional proteins

Question 29

Assembly and maturation

Answer 29

Assembly of virus genome and proteins into new virions follow a specific order
All components, including nucleic acids and proteins, are packages to form mature virions
May take place in nucleus, cytoplasm, plasma/cell membrane (enveloped viruses)

Question 30

Release of progeny virions

Answer 30

Naked virions: lysis of host cell
Enveloped virions: budding

Naked cant do budding bc they dont have an envelope

Question 31

Exocytosis

Answer 31

Viruses mature by budding through the membranes of golgi apparatus or ER.
Vesicles containing the virus then migrate to the plasma membrane and released by exocytosis
Viruses that acquire the envelop while budding from ER membrane leave infected host cell by exocytosis

Question 32

Replication of retroviruses

Answer 32

Reverse transcriptase: synthesized RNA into DNA

Integrase: integrated viral DNA into host genome

Question 33

Cell-to cell spread

Answer 33

Extracellular spread- released to outside travel to new cell
Intercellular spread- cell to cell without contact with extracellular milieu
Nuclear spread- passed down to progeny of host cell