Lecture 1: General Virology 2

Question 1

Define viral replication

Answer 1

Viral replication: formation of virions in host (extracellular or intracellular form)

Question 2

What does viral replication lead to

Answer 2

• Lead to productive replication
  o Can switch between non productive stage (herpes latency)
  o Spread in host (via lymphatics or blood) > release (mucosal surface/blood)> transmit

Question 3

How to detect viral replication?

Answer 3

immunostaining or PCR (genome detect) or electron microscopy (whole virus visualize)

Question 4

What is the significance for a virus having a larger genome size

Answer 4

• Only a few structural proteins are actual required
• Circovirus: Circular genome with 2 open reading frames (only 2 proteins made)
• Larger DNA viruses can code for many more (more non-structural proteins)
  o Extra proteins used to downregulate immune system/cell cycle (regulate MHC1/PRRs/apoptosis pathways…)

Question 5

What are the 8 steps of viral replication

Answer 5

Steps of Viral Replication
1. Virus attach to receptor
2. Nuclear capsid (genome + capsid) endocytosed (not envelope)
3. Penetrate endosome in cytosol
4. Migrate to relevant part of cell (ex. DNA virus go to nucleus)
5. DNA replication
6. Protein production
7. Assemble proteins + add genome
8. Release new virions

Question 6

Define the eclipse period in viral replication

Answer 6

• Eclipse period: time after virus enters cell until new viral proteins are maturing

Question 7

Define the latent period in viral replication

Answer 7

• Latent period: time from viral entry until release (uncoat +maturation)

Question 8

Describe tissue tropism

Answer 8

Tissue tropism: ability of a virus to infect a particular organ
* Susceptibility: cells have specific receptor
* Permissivity: cell machinery can support viral genome

Question 9

How do viral particles identify cellss to enter

Answer 9

Viral Receptors

Attach to membrane surface molecules
* Different viruses can bind same receptor or different ones – some have multiple

Question 10

How to envelope viruses enter cells

Answer 10

1. Bind receptor
2. Fuse envelope bilary with cell membrane
3. Internalize Capsid and genome via endocytosis
4. Genome break out of capsid – uncoating

Question 11

How to naked viruses enter cells (2 ways)

Answer 11

Receptor mediated endocytosis
1. Bind cell receptor
2. Entire virus endocytosed
3. Genome breaks out – uncoat
Pore-forming: picornaviruses
1. Bind receptor
2. Release pore forming peptide (on capsid) – penetrate cell membrane
3. Only genome injected into host cell

Question 12

What step of protein production is used by all viruses

Answer 12

translation

Question 13

What enzyme is used in the nucleus to convert DNA to mRNA

Answer 13

DNA dependent RNA polymerase

Poxvirrus carries its own

Question 14

What types of viruses replicate in the cytoplasm, nucleus, or both?

Answer 14

• RNA virus: cytoplasm – because ssRNA(-) have own RNA dep RNA pol
• DNA virus: nucleus (except Poxvirus) – use host pol
• Hepadnavirus + retrovirus: both cytoplasm (reverse transcription) and nucleus (transcription)

Question 15

Describe the steps of DNA virus replication? Specifically, herpesvirus

Answer 15

Herpes virus transcription
* Regulated transcription
1. Enter cell and go to nucleus
2. Produce many types of mRNA
o A – Block immune response and stimulate B production
o B – stimulate replication of genome and y production
o Y – stimulate structural protein mRNA production (capsid)
3. Package genome and protein and glycoproteins
4. Pinch off in cell membrane to create envelope

Question 16

Describe the steps of RNA virus replication

Answer 16

RNA virus replication (flavivirus)
1. Enter cell
2. + sense RNA translated into poly protein
3. Poly protein is modifies via post translational cleavage

Question 17

Describe the steps of Retroviral virus replication

Answer 17

Retrovirus replication (EIA virus)
1. Enter cell (carrries reverse transcriptase and integrase) via receptor
2. Uncoat
3. Viral RNA > ssDNA via viral reverse transcriptase
4. SsDNA > dsDNA > go to nucleus and integrate into host genome
5. Create viral RNA
6. Package to form nascent virion (not mature) > exit
o Nascent virion still has Gag and Pol glycoproteins – not infectious
7. Cleave glycoproteins extracellularly = mature

Question 18

What makes retroviruses unique

Answer 18

they incorporate their genome into the host genome

meaning it is LIFELONG infection

Question 19

Compare exit strategies of enveloped and non-enveloped viruses + examples of enveloped

Answer 19

Enveloped
* Only infectious if it has its envelope
* Via budding from various cell surfaces
* Ex.
o Mucosal surface: Influenza/rabies/paramyxovirus
o Basal cell surface: alphavirus/vesicular stomatitis virus/lentivirus
o ER/golgi: coronavirus/flavivirus/hepadnavirus
o Nucleus: herpes
Non-Enveloped
* Via cell lysis

Question 20

Viruses cannot replicate in

• plants
• birds
  -mammals
  -bacteria
  -water

Answer 20

water

Question 21

Which cellular functions are used by all viruses?

A Energy production
B Carbohydrate synthesis
C Transport
D Lipid synthesis
E Nucleic acid synthesis

Answer 21

E Nucleic acid synthesis

Question 22

An essential component of all virus particles is

A Minerals
B Carbohydrates
C Vitamins
D Proteins
E RNA

Answer 22

D Proteins

Question 23

Presence of envelopes in some viruses

A Make them resistant to Natural killer cell attack
B Make them susceptible to Natural killer cell attack
C Make them resistant to cytotoxic cell attack
D Make them susceptible to cytotoxic cell attack
E Make them susceptible to chemical detergents

Answer 23

E Make them susceptible to chemical detergents

Question 24

Some naked viruses deliver the viral genome across host cell membrane by

A Fusion of host cell membrane and viral envelop
B Attaching to a transport protein
C Phagocytosis
D A pore that is formed by protein components of the
viral capsid
E None of the above methods

Answer 24

D A pore that is formed by protein components of the
viral capsid

Question 25

A unique feature of replication of retroviruses is

A Viral entry via a pore made in the cell membrane
B Egress of progeny viruses by host cell lysis
C Reverse transcription
D Use of cellular machinery for energy metabolism
E Viral protein synthesis in ribosomes

Answer 25

C Reverse transcription

Question 26

A unique feature of replication of herpesviruses is

A Viral entry via a pore made in the cell membrane
B Egress of progeny viruses by host cell lysis
C Reverse transcription
D Viral replication in viroplasm
E Highly regulated viral replication in host cell nucleus

Answer 26

E Highly regulated viral replication in host cell nucleus

Question 27

Poxvirus replication when compared to that of other
DNA viruses is unique due to

A Viral entry via a pore made in the cell membrane
B Use of host cell polymerases for DNA replication
C Reverse transcription step during viral replication
D Viral replication in cytoplasm
E None of the above

Answer 27

D Viral replication in cytoplasm