Virus replication

Question 1

Define transfection

Answer 1

introduction of viral genetic material into the cells artificially

Question 2

Define infection

Answer 2

replication of virus through normal route of entry into susceptible cells

Question 3

Define susceptibility

Answer 3

Susceptible cell has receptor for specific virus + supports replication of that virus

Question 4

In order for a cell to be susceptible to infection, what two things must it have?

Answer 4

receptor specific for the virus

support replication of virus

Question 5

Define permissiveness

Answer 5

cells lack receptor for particular virus, however, if virus or viral genome is introduced artificially –> cell supports virus replication

Question 6

Where do DNA viruses replicate? RNA?

Answer 6

DNA: nucleus except poxviruses and asfarviruses
RNA: cytoplasm except retrovirus, orthomyxoviruses and reoviruses

Question 7

What normal eukaryotic host cell enzymes are used for nucleic acid replication?

Answer 7

DNA-dependent DNA polymerase – DNA synthesis

DNA-dependent RNA polymerase – mRNA synth

Question 8

What are some viral enzymes for nucleic acid replication?

Answer 8

1. Reverse transcriptase (RNA dependent DNA polymerase)
2. RNA dependent RNA polymerase
3. DNA dependent RNA polymerase, if DNA replicates in cytoplasm

Question 9

What are the 6 steps in viral replication?

Answer 9

1. Attachment
2. Penetration/Entry
3. Uncoating
4. Synthesis of viral components (Replication, viral protein synthesis)
5. Assembly
6. Release

Question 10

What are the 4 mechanisms for viral penetration (entry of virion or genetic material)?

Answer 10

1. Translocation - entire virus crosses
2. Endocytosis or pinocytosis - entire virus is wrapped by cell membrane –> engulfed –> accumulation in cytoplasmic vacuoles (adenovirus)
3. Fusion - fusion of viral envelope with cell membrane (herpesvirus) –> no cytoplasmic vacuole
4. Injection - NA is injected into cell (bacterial virus)

Question 11

What is uncoating?

Answer 11

release of viral NA for gene expression

Question 12

What is viral assembly?

Answer 12

packaging or encapsidation of viral NA within protein coat

Question 13

What are 7 virus types creating the different assembly mechanisms?

Answer 13

1. Linear dsDNA viruses
2. Circular dsDNA viruses
3. dsRNA virus
4. Helical ssRNA or ssDNA viruses
5. Icosahedral ssRNA viruses
6. Icosahedral ssDNA viruses
7. Retroviruses and hepatitis B virus

Question 14

What enzyme is used to synthesize mRNA?

Answer 14

DNA-dependent RNA polymerase

Question 15

Where does the viral envelope come from?

Answer 15

Release by budding – envelope = host cell membrane

Question 16

What is the early period? Late period?

Answer 16

Early period: before the start of viral NA replication

Late period: after start of viral NA replication

Question 17

What is an early gene?

Answer 17

viral gene that express b/f NA replication

Question 18

What do most early genes encode for?

Answer 18

Enzymes or factors that help in virus replication

Question 19

What is a late gene?

Answer 19

viral gene that express after NA replication

Question 20

What do late genes encode for?

Answer 20

viral structural proteins and factors for assembly

Question 21

What are the 4 phases of viral replication?

Answer 21

1. Eclipse phase
2. maturation phase
3. Released
4. Inactivationo

Question 22

What is the eclipse phase?

Answer 22

attachment, penetration and uncoating have taken place.

synthesis of viral components may have started

Question 23

What is the maturation phase?

Answer 23

virus assembled

Question 24

What is the released phase?

Answer 24

get out of the cell

Question 25

What is the inactivation phase?

Answer 25

loss of virus infectivity

Question 26

What phase of viral replication may we not be able to isolate the infectious virus?

Answer 26

Inactivation phase

Question 27

What type of viruses have assembly of virion inside the nucleus?

Answer 27

dsDNA and ssDNA

Question 28

What is the general replication process of the dsDNA?

Answer 28

entry into nucleus
replicate and transcribe (mRNA)
mRNA –> cytoplasm –> viral proteins –> nucleus
viral proteins + DNA replicated = assembly of virion
ER –> envelope aquired –> release

Question 29

What is the general replication of ssDNA?

Answer 29

entry into nucleus
ssDNA –> dsDNA
transcribed into mRNA (nucleus)
–> genome replication + viral protein –> assembly –> release

Question 30

What is the general replication process of + sense ssRNA?

Answer 30

entry into cell –> cytoplasm
transcription and replication –> mRNA + genome
viral proteins + ssRNA ==> assembly –> release

Question 31

What enzyme is negative sense ssRNA transcribed by when in the host cell?

Answer 31

viral RNA polymerase –> makes mRNA

Question 32

How can we apply the knowledge of viral replication?

Answer 32

1. Cultivation
2. Diagnosis
3. Prevention (vaccination, disinfection)
4. Treatment

Question 33

What are two ways influenza viruses change?

Answer 33

Antigenic drift

Antigenic shift

Question 34

What is antigenic drift?

Answer 34

Slow, small change
Occur through point mutation in main surface proteins (hemagglutinin, neuraminidase)
Changes are unpredictable and minor

Question 35

What is antigenic shift?

Answer 35

Abrupt, and major
producing new strain not previously seen
occur through direct animal to human transmission or through genetic reassortment.

Question 36

What type of virus change can cause worldwide pendemics?

Answer 36

Antigenic shift –> new strain not previously seen