Virus Replication

Question 1

What determines the pathogenic potential and tropism of a virus?

Answer 1

Identity, location, density, and function or cell receptors and attachment factors

Question 2

What are cell receptors?

Answer 2

Receptors on the cell membrane that have a normal function for the cell. Provide a place for viral attachment. Viruses evolve to attach the receptors for entry.

May send signals that attract viruses

Question 3

What are attachment factors?

Answer 3

less specific

do not promote virus attachement via signals

Question 4

Steps of virus entry (5)

Answer 4

1. Bind via receptors, attachment factors, co-receptors
2. Signal, conformation changes, fusion or internalization
3. Transport to endosomes
4. Release from endosome via cures such as low pH
5. Transport to cytosol or nuclues - uncaring of nucleic acids

Question 5

How do receptors bind to virus?

Answer 5

Viral envelope
* glycoprotein attachment

Non enveloped

• attach to protein projections directly from capsid
• attach to “canyons” of the capsid

Question 6

Once virus is attached to receptor what can occur?

Answer 6

May trigger fusion or other steps for entry
May send cellular signals enhancing viral entry and infection
Co-receptors may bind and cause secondary changes

Question 7

What can occur if virus attaches to attachment factors?

Answer 7

Proteoglycans help concentrate visions on cell surface and increase efficiency

Question 8

Movement of viruses outside of the cell

Answer 8

FILOPODIA - help translocate the virus to find a receptor

Question 9

Movement of viruses inside the cell

Answer 9

ACTIN and MICROTUBULE machinery

*nuclear or cytoplasmic

Question 10

Endocytosis is used for virus entry. Why is this beneficial?

Answer 10

Virus fuse directly with plasma membrane

• free ride to nucleus (cytoplasm is crowded)
• Doesn’t leave traces for immune detection
• Multiple pathways - allows flexibility and more tropism
• use cell signals in endosome (low pH) to facilitate uncoating and release
• virus can trigger macropinocytosis

Question 11

How does a virus get out of the endosome?

Answer 11

Enveloped viruses:

• fuse with membrane and release into cytosol
• change acid content creates membrane permeability

Nonenveloped:
* penetrate the vesicle membrane by puncture, perforation, or lysis

Question 12

What is the NPC?

Answer 12

Nuclear pore complex

Question 13

How do viruses get genomic material into nucleus?

Answer 13

Through the NPC - different viruses achieve this differently

Question 14

RNA viruses enter nucleus how?

Answer 14

Do not have a capsid

** will enter directly through the NPC **

Question 15

Hepadnaviridae enters nucleus how?

Answer 15

capsid enters NPC but remains attached to it and releases the viral genomic DNA into the nucleoplasm

Question 16

ssDNA virus enters how?

Answer 16

capsizes are small enough to cross NPS and enter nucleus with intact capsid – will release from capsid inside nucleus

Question 17

Herpesvirales capsid enters how?

Answer 17

Too large to enter NPC – viral genome is directly injected through NPC

Question 18

Retroviruses enter how?

Answer 18

during mitosis with the nuclear membrane is degraded

Question 19

Obstacles for replicating viral genome (4)

Answer 19

which polymerase
where to replicate
how to transcribe to make mRNA
how to generate protein in the right proportions at the right time

** these can lead to targets for drug therapy **

Question 20

dsDNA viruses use _____ DNA polymerase or ____ ____ ____

Answer 20

cellular
make their own

• • HERPES
• • PAPILLOMA
• • POLYOMA

Question 21

ssDNA first replicate their DNA using _____ DNA polymerase

Answer 21

cellular

• • PARVO
• • ANELLO
• • CIRCO

Question 22

some dsDNA make their own ______ transcriptase

Answer 22

virion

** POX

Question 23

Viruses that use cellular RNA polymerase or cellular DNA polymerase are easier or harder to target for treatment?

Answer 23

Harder - pose toxicity to the host

Question 24

+ strand RNA viruses make protein _______ from their genome

Answer 24

Directly

• genome acts as mRNA

Question 25

• strand viruses must make ___ ________ RNA polymerases to make mRNA

Answer 25

RNA dependent

Question 26

Retroviruses must ______ transcribe their RNA and use ____ RNA polymerase

Answer 26

Reverse

Cellular

Question 27

DNA viruses that use host DNA polymerases …..

Answer 27

fully dependent on host functions.

transport nucleus to replicate their DNA and transcribe mRNA

Question 28

DNA viruses that make their own DNA polymerase and a whole replication complex….

Answer 28

Make special transcription factors to preferentially transcribe their genes.

• carefully controlled
  * immediate early
  * early
  * late

Viruses that can replicate in the nucleus can splice genes! Rearrange to make special combinations - doesn’t wast resources

** HERPES

Question 29

Herpes

Answer 29

Latent and Lytic stages
* latent:
the virus exists as a plasmid - bound to chromosome
replicated passively by host DNA replication
restricted –

• lytic
  linear genomes are produced by rolling circle mechanism

Question 30

+ strand RNA replicate in the CYTOPLASM

Answer 30

produce + and - strands

multigened mRNA is translated into polyprotein – cleaved into separate proteins

Question 31

• strand ssRNA virus replication

Answer 31

occurs in the NUCLEUS
RNA dependent RNA polyermase (creates an RNA template from RNA)
Antigenote is used for both translation and as a replication template
* coated to prevent translation when used as a template for replication