L19

Question 1

what is a virus

Answer 1

• piece of DNA/RNA, enclosed in a protective coat
• parasitic
• purpose is to deliver its genome into the host cell so it can be expressed

Question 2

define capsid, nucleocapsid, envelope, and virion

Answer 2

capsid- protein shell surrounding genome
nucleocapsid- consists of the capsid with the enclosed nucleic acid
envelope- viral membrane, host cell derived lipid bilayer
virion- infectious virus particle

Question 3

define viral proteins

Answer 3

• virus hijacks hosts cellular machinery to support their replication
• so viral protein mostly structural components, e.g. viral membrane + capsid

Question 4

what is the function of structural proteins

Answer 4

• protection of the genome
• form envelope
• recognition
• packaging of nucleic acid
• ## delivery of genome

Question 5

how are viruses named/classified

Answer 5

• by disease caused
  -morphology
• function
• shape of nucleocapsid

Question 6

helical viruses: nucleocapsid classifications

Answer 6

helical viruses
- e.g. tobacco mosaic virus
- infects plants
- slinky shaped capsid, twists around to enclose genetic material

Question 7

polyhedral viruses: nucleocapsid classifications

Answer 7

polyhedral viruses
- adenovirus
- capsids made of genetic material, surrounded by 20 triangular faces

Question 8

spherical viruses: nucleocapsid classifications

Answer 8

• corona virus
  -helical, enclosed in a envelope with spiked sugary proteins (help with sticking/entering host cells

Question 9

complex viruses: nucleocapsid classifications

Answer 9

• bacteriophages
• lunar lander
• polyhedral head and a helical body (tail sheath) + legs (tail fibres), help transfer genetic material

Question 10

stages of viral replication

Answer 10

• attachment + fusion: hemagglutin on influenza virus becomes attached to sialic acid sugars on target cell (commonly throat, lungs, nose)
• penetration: cell engulfs the virus by endocytosis, 2 mechanisms- fusion (virus fuse with cell membrane) or endocytosis (virus enter cell by endocytosis, or virus enclosed in vesicles in cytoplasm)

-uncoating: viral contents are released

-biosynthesis (replication): viral RNA enters the nucleus, where it is replicated by the viral RNA polymerase

• assembly: new phage particles are assembled

-release: new viral particles made + released into extracellular fluid, cell continues to make new virus, endocytosis

Question 11

uncoating strategies

Answer 11

• pore formation
• plasma membrane fusion
  -direct uncoating
• partial uncoating- HIV
• endosomal fusion- influenza
  endosomal lysis with nuclear membrane- adenovirus

Question 12

explain RNA dependent RNA polymerase

Answer 12

• RNA viruses replicate in cytoplasm via RNA polymerase
• host cells lack RNA dependent RNA polymerases needed for the replication of viral RNA, so virus needs to provide the enzyme itself
• the viral RNA dependent RNA polymerase acts as a transcriptase (transcribe mRNA) as well as replicase (Replicate RNA genome)

Question 13

what is viral maturation

Answer 13

• preparation of the virion for subsequent infection of other cells
• occur inside cell of after release

Question 14

what are the 2 methods for the release of virions

Answer 14

lysis- naked viruses released as host cell lysed
budding- enveloped viruses by through host membrane

Question 15

what is the viral cytopathic effect

Answer 15

• refers to the change in cell morphology caused by infecting viruses
• caused by lysis
  e.g. rounding of infected cell

Question 16

what is a provirus, and difference between a prophage

Answer 16

• inactive
• result of virus undergoing lysogenic cycle
• provirus is the genome of the virus, prophage is the genome of the phage structure