Virus Replication

Question 1

Viral Replication:

Steps

Answer 1

1. Receptor mediated
2. Attachment and Entry
3. Uncoating
4. Genome replications
5. RNA and protein synthesis
6. Assembly of nucleocapsid and maturation
7. Release form the cell

Question 2

Susceptible

Answer 2

has a receptor for a virus

Question 3

Resistant

Answer 3

does not have the receptor for a virus

Question 4

Permissive

Answer 4

Can replicate the virus

Question 5

Susceptible and permissive

Answer 5

The virus can enter the cell and replicate

Question 6

Viral Replication:

2. Steps for Attachment and Entry

Answer 6

• Virions have to diffuse across the plasma membrane and then release the genome
• Steps for attachment and entry:
  
  • Adhere to the cell surface
    
    • not specific, happens by chance since they cannot move
  • Attache to a recepto
    
    • these receptors are not made for the virus they are receptors for proteins that the cell normally needs
    • Genome is then transferred into the cell

Question 7

Viral Replication:

2. Entry:

Answer 7

Once the virus enters it is transported to the correct location

CME = Clathrin-mediated endocytosis

Question 8

Viral Replication:

3. Uncoating

Answer 8

Acidic condition in the endosome triggers changes in viral structural proteins resulting in uncoating and release of the viral genome

Question 9

Viral Replication:

make mRNA

Answer 9

Transcription

Question 10

Viral Replication:

4. Transcription of Viral Genes

DNA genome Viruses

Answer 10

Host or virus DNA-dependent RNA polymerase generates viral mRNA

mRNA is translated into viral proteins using cellular machinery

Question 11

Viral Replication:

4. Transcription of viral genes

RNA genome Viruses

Answer 11

Require a viral-encoded RNA-dependent RNA polymerase (RdRp) to make mRNA

There is no cellular RdRp to copy RNA form a viral RNA template.

Virus must possess or synthesize RdRp

Question 12

Viral Replication:

5. Translation of mRNA to make viral proteins

Answer 12

• Translate the mRNA into protiens
• Compare to cell mRNA
  
  • 5’ cap UTR AUG ORF stop UTR AAAAAA 3’
• Ribosomes are needed for translation
• tRNA also needed to add the correct amino acids
• Translation also needs
  
  • initiation
  • Elongation
  • Termination proteins

Question 13

Viral Replication:

5. Virus Replication:

Viral Genome synthesis:

DNA viruses

Answer 13

most replicate in the nucleus

except poxvirus and mimivirus

Most us the host DNA-dependent DNA polymerase

Except poxvirus and herpesvirus

Question 14

Viral Replication:

5. virus replication

Viral genome synthesis

RNA viruses

Answer 14

most use viral encoded RNA-dependent RNA polymerase

except retroviruses that use reverse transcriptase

Quasispecies - not two viral genomes are identical

Question 15

Viral Replication:

5. Translation of Viral Proteins

Answer 15

• All viruses use cell machinery for making proteins
• Viral protiens:
  
  • often named based on timing of synthesis
• Early Translation Products:
  
  • mostly nonstructural protiens
• Late Translation Products:
  
  • Structural proteins

Question 16

Viral Replication:

6. Assembly of nucleocapsids and Virus maturation

Answer 16

• Self assembly of the capsid:
  
  • many viral proteins assemble on their own
    
    • HIV poliovirus, Influenza HA
  • Empty shells can be the basis for vaccines
• Assisted Assembly:
  
  • some need scaffold and chaperones from the cell to form the viral structure
• All viruses have to:
  
  • form the protein chell from one or many viral proteins
  • Assemble the protein shell
  • Release the virion from the host cell
• Some viruses have to:
  
  • Acquire an envelope
  • Go through virion maturation

Question 17

Viral Replication:

7. Budding or Release from the cell

Envelope

Answer 17

Normally happens after the assembly of the nucleocapsid then buds

There are four strategies for budding

Question 18

Viral Replicaiton:

7. Budding or Release from the cell

Budding:

Answer 18

Depending on the virus, budding can occur form any membrane compartment

Can make a double membrane on the virus

Question 19

Viral Replication:

7. Budding or Release from the cell

How can viruses exit the cell

Answer 19

• Important for pathogenesis:
  
  • budding:
    
    • aquires a membrane
  • Lysis:
    
    • break the cell open and release the virion
  • Release viruse without lysis (poliovirus)
  • Move from cell to cell without cell lysis

Question 20

Viral Replication:

dsDNA virus:

Steps 1-3

Answer 20

Herpesvirus Replication - replicates in the nucleus

• Protein vhs:
  
  • cuts up the host cell mRNA which blocks host cell defenses
• Protein VP16:
  
  • facilitates the transcription of herpesvirus RNA

Question 21

Viral Replication:

dsDNA virus:

Steps 4-5

Answer 21

Herpesvirus replication - replicates in the nucleus

• Three types of mRNA produced by the virus
  
  • a - immediate earyly
  • B - early
  • y - late

Question 22

Viral Replication:

+RNA virus (Coronavirus)

Answer 22

Replicates in the cytoplasm

Buds in the ER/Golgi

Only makes 8 viral proteins

Question 23

Viral Replication:

Retrovirus

Answer 23

Retroviruses have a provirus step

They replicate in the Nucleus for the DNA step

If a retrovirus infects a germ cell there cen be a generational infections (vertical transmission)

When the cell divides the virus divides with it because of hte provirus