Heaphy 6 viral replication

Question 1

Reasons virus have to replicate in cell:

Answer 1

• Attachment & penetration of cell
• Uncoating, nucleic acid &protein synthesis in cytoplasm
• Assembly & exit (nucleolus/cytoplasm/plasma membrane)
• Diffs = defective interfering patricles (non-harmful

Question 2

Multiplicity of infection MOI

Answer 2

• Study of synchronously infected cells is useful. (add viruses to cells to allow it to replicate to average the replication events in many cells simultaneously)
• Growth curve =>

Question 3

Colony:

Answer 3

plaque forming

Question 4

Eclipse phase:

Answer 4

1 low amounts of parental infectious material present. Genome replication has been initiated. Duration, minutes-hrs.

Question 5

Maturation phase:

Answer 5

2 viral material accumulates in cell/ surrounding medium. shed from infected cell

Question 6

Lytic viruses:

Answer 6

become metabolically disordered and die, viral production ceases. Titres (numbers) slowly drop.

Question 7

Non lytic viruses:

Answer 7

viruses can continue to produce viral particles indefinitely.

Question 8

Reproductive cycle:

Answer 8

less than an hour with many bacteriophage, 6-8hrs in picornaviridae and more than 40 hrs in herpesviridae.

Question 9

lag phase:

Answer 9

virus particle attach & penetrate => synthesis & assembly (same as eclipse phase)

Question 10

Productive:

Answer 10

i.e. entry into permissive cells followed by virion formation.

Question 11

Abortive:

Answer 11

i.e. entry into a non permissive cell which does not result in virion formation; many reasons for non-permissiveness e.g. no receptor.

Question 12

Eestringent or restrictive:

Answer 12

cell is transiently permissive and a few virus are produced. Virus production stops but the genome remains in the cell, e.g. Epstein Barr Virus and herpes simplex virus. May still have serious consequences e.g cancer.

Question 13

ATTACHMENT

Answer 13

1 energy independent • virion attachment protein or anti-receptor binds to a cell surface receptor. often glycoproteins

Question 14

UPTAKE

Answer 14

2 energy dependent
• Endocytosis : entire particle => accumulation of virus particles inside a cytoplasmic vesicle,an endosome, e.g influenza.
• Fusion of the cellular membrane with virion envelope & direct release of the capsid into the cytoplasm e.g. HIV.

Question 15

UNCOATING

Answer 15

3 • events after penetration allows virus to express its genome .
• viruses capsid only ever partially disintegrates & replication takes place in a structured particle.

Question 16

GENE EXPRESSION

Answer 16

4 genes are expressed

Question 17

ASSEMBLY

Answer 17

5 • Filamentous virus assembly e.g. TMV. Protein aggregation and RNA recognition.
• Icosahedral assembly e.g. polio. Twelve pentamers form particle.

Question 18

EXIT

Answer 18

6 • cell lysis: Picorna unenveloped.

• bud through a cell membrane, acquiring an envelope. Can be the plasma membrane e.g. HIV-1.