Viruses

Question 1

Viruses -features

• lifecycle overview
• how they get onto cells

-fungal viruses

Answer 1

• Are v. small & abundant
• Virus: a nucleic acid and a protein coat (and sometimes a lipid envelope)
• Infects cell then reproduces w/in it, releases a progeny of virus (and then starts cycle again)
  
  • Viruses use the cell components in reproduction phase although some do use their own viral components (i.e. viral polymerase)
• protuberances on surface enable it to implant onto & get into cell

*fungal viruses don’t seem to have negative effect - tho not many around

Question 2

Common shapes of Viruses (3)

Answer 2

• Compact icosahedral (phiX174)
• Spherical (HIV)
• Filamentous (TMV)

Question 3

Genomes of Viruses

• Types
• Retroviruses

Answer 3

-Can be s.s or d.s., RNA or DNA

Retroviruses: have RNA genome

• RNA genome converts into DNA and then converted back to RNA
• integrates into host DNA
  
  • large portion of genome contains these retroviruses & their sequences
• ds DNA viruses = largely animal viruses (are some plant ones)
  
  • also includes bacteriophage

Question 4

Structure of Viruses

Answer 4

• Genomic material immediately surrounded by capsid protein
• Can have a lipid envelope if buds off from cell (rather than cell going through lysis)
• Virus can get out of cell via exocytosis or lysis - either way, still is loads of virions released
  e. g. when E. coli infected by 1 phage lambda particle, it lyses and releases > 10^6 progeny particles

Question 5

Steps of replication of Lentivirus (a retrovirus)

Answer 5

• RNA genome -> translated to give reverse transcriptase -> grabs the RNA genome and copies it into cDNA -> RT integrates this it into cDNA
• following transcription & translation, RNA & proteins formed come together to form progeny virus - are then released from the cell

Question 6

Significance of Viruses

Answer 6

1. Interested in viruses because they cause disease
   
   • understanding replication, can interrupt lifecycle
2. Also useful as cloning vectors
   
   • especially retroviruses (can integrate our gene into retrovirus genome, then infect cell with retrovirus)
3. Viruses also used to deliver vaccines - inject viral DNA into tissue and it’s expressed - gives rise to immune response