CBG21

Question 1

What is the generalised life cycle of a virus?

Answer 1

1. entry into cell and uncoating.
2. transcription - replication
3. translation
4. assembly of progeny virus and exit from cell

Question 2

What are the 3 phases seen on sigmoidal curve of viral infection

Answer 2

1. eclipse phase (lagging) - corresponds to period in which in out virus becomes uncoated. no infectious virus detected at this time.
2. synthetic phase. - time during which new particles are assembled
3. latent period - no extracellular viruses detected

Question 3

What determines which cells a virus infects, what is this known as?

Answer 3

different cellular receptors on the cell surface

cell or tissue tropism

Question 4

What does retrovirus HIV-1 show?

Answer 4

cellular tropism
mutations allow switching between target cells
can infect macrophages and t cells

Question 5

Where does viral replication happen for dna and rna viruses?

Answer 5

most dna viruses replicate in the nucleus
- except paxvirus
most rna viruses replicate in the cytoplasm
-except retroviruses

Question 6

What does - sense RNA virus have that + does not?

Answer 6

RNAP in virion particle so it can become positive
sense.
negative sense by itself cannot causes infection needs to become postivie to do so

Question 7

what must retroviruses carry?

Answer 7

a reverse transcriptase, to make dna out of rna

Question 8

How do viruses often exploit host?

Answer 8

transcription often uses host polymerases
- many host transcription factors bind to viral rna thus increasing/controlling expression
transaltion uses hosts ribosomes
- viral proteins often cleaved by host proteases

Question 9

Where does capsid assembly generally occur?

What about viruses with envelops.

Answer 9

at the site of viral replication.
often self assembly
viruses with envelops are assmebled on the surface of the cell or subcellular compartments
viral membranes are derived from host

Question 10

what can different number of viral membranes relate to?

Answer 10

different no. of viral functions

Question 11

What are the two genes that the virus could technically go through life cycle containing only these

Answer 11

gag - makes protein capsid
env- envelope protein code
rest of genes are defensive etc

Question 12

How does HIV enter the cell?

Answer 12

• proteins on envelope
• fuses with cell membrane
• uncoating
• virion without envelope released into cell
• fusion can only occur if virus has envelope membrane

Question 13

How does influenza enter the cell?

Answer 13

• proteins on envelope
• enters cell by endocytosis
• in cell as endosome
• pH change causes fusion between viral and endosomal membrane eads to uncoating releasing vRNA

Question 14

How does polio enter the cell?

Answer 14

polio has no envelope
enters cell via receptor mediated endocytosis
capsid not just protecting also binding to cellular receptors.

Question 15

Describe polio

Answer 15

ssRNA
+ sense
no envelope
replicates in cells of gastrointestinal tract

Question 16

How does adenovirus enter the cell?

Answer 16

enters cells via receptors on evelope 
endocytosis
followed by acidification of endosome
causing capsid proteins to break apart
uncoating
and released of dsDNA into nucleus

Question 17

Describe adenovirus genome

Answer 17

dsDNA genome
non enveloped
broad range of vertebrate hosts.

Question 18

What is surface assembly viral budding?

Answer 18

when capsid particles enclose genetic info
and it buds out of the cell
using host membrane