Viral Replication

Question 1

Most DNA viruses replicate in the ________, most RNA viruses replicate in the _______

Answer 1

Cell nucleus; cytoplasm

Question 2

What 2 DNA viruses replicate in the cytoplasm?

Answer 2

• poxviridae

- African swine fever

Question 3

What RNA viruses replicate in the nucleus?

Answer 3

• orthomyxoviridae
• retroviridae
• some paramyxoviruses (canine distemper)

Question 4

Replication cycle outline

Answer 4

• attachment or adsorption
• penetration or uptake
• uncoating
• synthesis of viral nucleic acid and protein
• assembly/ maturation
• release

Question 5

Attachment/adsorption

Answer 5

Virus attaches to cell surface

• occurs via ionic interactions (temp independent)
• recognizes specific receptors on cell surface –> cells without receptors are not susceptible to the virus!

Question 6

Penetration

Answer 6

Virus enters the cells

Question 7

What are 2 ways enveloped viruses can enter cells?

Answer 7

• fusion: entry via fusing with plasma membrane
• endocytosis: entry by endosomes at the cell surface
• -> virus taken up by invagination of clathrin-coated pits into endosomes

Question 8

Endocytosis

Answer 8

Endosome becomes acidified –> virus membrane fuses with endosome membrane
- fusion of endosome and viral membrane = release of internal components of virus

Question 9

Penetration for non-enveloped viruses

Answer 9

Virus crosses plasma membrane directly, or is taken up via clathrin-coated pits into endosomes
- virus directly crosses endosome membrane

Question 10

Uncoating

Answer 10

Nucleic acid must be uncoated before virus replication can begin
- after uncoating, infectious virus particles cannot be recovered from cell (lasts until new infectious virions are made)

Question 11

Assembly/maturation

Answer 11

Maturation may follow the initial assembly process
- viruses in final stage of assembly go thru a set of structural transitions and/or biochemical modifications that transform recursor particles into infectious particles

Question 12

Release

Answer 12

• cell lysis
• budding (does not have to kill host cell)
• not all released viral particles are infectious
• enveloped viruses released by budding from plasma membrane

Question 13

Structural protein

Answer 13

All proteins in a mature virus particles, even if they make no contribution to the morphology or rigidity of the virion

Question 14

Non structural protein

Answer 14

Viral proteins found in the cell, but not packaged into the virion

Question 15

How do viruses affect host cells?

Answer 15

Many inhibit host RNA, DNA or protein synthesis

- damage the function of cells or kills cells

Question 16

Cytopathic effect

Answer 16

Morphological changes in the host cell caused by viruses

• consist of cell rounding, disorientation, swelling/shrinking, death, detachment from the surface
• depends on virus and cells on which it is grown
• will take a couple of inoculations to see CPE on artificial media

Question 17

Use of CPE

Answer 17

• identify virus isolate

- quantitate infectious virus particles by the plaque-forming unit

Question 18

Isolation and propagation of viruses

Answer 18

• animals
• embryos
• cell cultures

Question 19

The more virus passes or adapts in host cells, the more _______

Answer 19

Virulence the virus becomes to the host

Question 20

Preparation of specimen for inoculation

Answer 20

Fresh or frozen tissues –> homogenize –> freeze and thaw (rupture cell/release virus) –> low speed centriguation and filtration –> spin down viruses with ultra speed centrifugation

Question 21

Primary culture

Answer 21

First in vitro cultures of cells taken directly from the organs
- requires death of animal hosts

Question 22

Cell line

Answer 22

Cell line that can be subcultured and grow continuously

• ex: tumor cell that can be subcultured for many passages
• do not need to kill host

Question 23

Growth of virus in cultured

Answer 23

• choice of cultured cells
• recognition of viral growth
• growth of virus in lab animals
• growth of virus in embryos-chicken embryonic eggs

Question 24

A virus contains DNA and RNA

Answer 24

False

Question 25

Viruses must have either double-stranded DNA or RNA

Answer 25

False

Question 26

All viruses have an envelope

Answer 26

False

Question 27

Viruses can be propagated in rich artificial media without cells

Answer 27

False | - cannot make proteins on their own

Question 28

Adenoviridae

Answer 28

- site of replication: nucleus - eclipse period (hr): 10 - budding (membrane): none

Question 29

Herpesviridae

Answer 29

- site of replication: nucleus - eclipse period (hr): 4 - budding (membrane): nuclear

Question 30

Poxviridae

Answer 30

- site of replication: cytoplasm - eclipse period (hr): 4 - budding (membrane): golgi

Question 31

Retroviridae

Answer 31

- site of replication: nucleus - eclipse period (hr): 10 - budding (membrane): plasma

Question 32

Only enveloped viruses can do _______, but both enveloped and nonenveloped viruses can do _________

Answer 32

Fusion; endocytosis

Question 33

Are all progeny created from replication infectious?

Answer 33

NO | - could be noninfectious due to mutations, etc

Question 34

You do not know if a virus is present within a cell without ______

Answer 34

CPE | - each virus has its own unique CPE