Module 2: Viruses

• virus components:

  • nucleic acid: RNA or DNA
  • capsid: proteins surrounding nucleic acid
  • envelope: membrane and viral proteins
• naked viruses have no envelope
• virus genomes can have DNA or RNA, single stranded or double stranded
• rod: RNA naked virus (plants)
• icosahedron: DNA naked virus with glycoprotein caps (cold)
• enveloped: RNA virus with membrane envelope and glycoproteins (influenza)
• complex: DNA virus with head and tail sheath (bacteriophage)
• + strand is coding, can be translated into a protein
• negative strand is template, can't be translated
• virus life cycle (lytic):

  1. attachment
  2. penetration
  3. synthesis
  4. assembly
  5. release
  6. maturation
• attachment: bind to structure (receptor) essential to host cell function
• penetration: enter cytoplasm

  • endocytic or non-endocytic (fusion at cell surface)
• synthesis: use host cell machinery and energy to reproduce
• assembly: multiple steps, can involve host and viral proteins
• release: budding (viral proteins assembled in host membrane) or lysis (kill cell and release all virus proteins)
• maturation: modify capsid to recognize new host and activate enzymes
• lysogenic cycle: virus inserts into host DNA
• DNA viruses use replication machinery of host
• RNA viruses make their own polymerase
• retrovirus (+ ssRNA) copy themselves into dsDNA intermediate
• QB viruse is + ssRNA, coding strand is translated by host into 4 proteins
• QB virus encodes own replicase to copy viral RNA
• QB virus is not regulated, lyses cell when enough maturation protein accumulates
• T4 virus is bacteriophage, large genome requires regulated cycle
• T4 virus lytic cycle:

  • early proteins prepare host
  • middle proteins replicate DNA
  • late proteins assemble
• bacteriophage delta is dsDNA, lysogenic or lytic
• what is the regulatory switch in bacteriophage delta?

  C2 protein
• stable C2 protein triggers lysogeny
• unstable C2 protein triggers lytic cycle
• actively growing cells have high FtsH protease
• how does FtSH protease affect C2?

  destabilizes, triggers lytic cycle
• prion: protein infectious particle
• prions are misfolded proteins that interfere with neural function