Week 9

• What do viruses rely on for replication?

  Host cell machinery
• What tools do viruses use from host cells?

  Synthesize proteins and replicate genetic material
• What are the roles of host cell organelles in virus replication?

  • Nucleus: viral DNA/RNA transcription
  • Ribosomes: translate viral mRNA into protein
  • Endoplasmic Reticulum: protein folding and viral assembly
  • Golgi apparatus: packages viral proteins
  • Mitochondria: provides energy for viral processes
  • Cell membrane: budding site for new viral particles

  
• How do viruses differ from cells in terms of growth?

  Viruses assemble rather than grow in size

  
• What marks the beginning of the viral life cycle?

  Inoculation phase
• What happens during the eclipse phase of the viral life cycle?

  Decline in extracellular viruses occurs
• What occurs after the eclipse phase in the viral life cycle?

  Virus assembles components within the host cell
• What is the maturation phase in the viral life cycle?

  Formation of complete virus particles

  
• What is the final step in the viral life cycle?

  Release of mature viruses from the host cell
• What are viruses classified as in terms of their relationship with host cells?

  Obligate intracellular parasites
• What are the main steps in the viral life cycle?

  1. Adhesion: Virus attaches to host cell
  2. Entry: Virus enters host cell
  3. Uncoating: Viral genetic material is released
  4. Synthesis & Assembly: Replication and assembly of new particles
  5. Virion Release: Newly assembled viruses are released

  
• What role do entry receptors play in virus infection?

  Determine host range and tropism

  
• Which receptor does the herpes simplex virus use?

  Heparan sulfate proteoglycan
• What receptor does the influenza virus bind to?

  Sialic acid
• Which receptor does poliovirus bind to?

  CD155
• What receptor does human herpesvirus 8 use?

  DC-SIGN
• Which receptor does foot-and-mouth disease virus attach to?

  Integrin (αvβ3)
• What receptors does HIV-1 utilize?

  CCR5 and CXCR4
• Which receptor does adenovirus bind to?

  CAR or integrin
• What are the general trends in virus-receptor interactions?

  • Different viruses can use the same receptor
  • Same virus can bind to multiple receptors

  
• What are the two modes of virus entry?

  1. Fusion: Viral envelope fuses with host membrane
  2. Uncoating: Viral capsid breaks down, releasing genome

  
• What is the difference between plasma membrane fusion and endosomal fusion?

  Plasma fusion is direct; endosomal uses vesicles
• What does uncoating refer to in the viral life cycle?

  Disassembly of the viral capsid
• What are the pathways of uncoating?

  1. Clathrin-mediated endocytosis
  2. Late endosome acidification triggers escape
  3. Release locations: cytoplasm or nucleus
• Why is it difficult for large particles to penetrate the cytoplasm?

  Cytoplasm contains dense structures and organelles
• How do large protein complexes move in the cytoplasm?

  Require active transport mechanisms
• How do viruses hijack the microtubule network?

  • Microtubules act as highways for transport
  • Viral particles attach to motor proteins
  • Dynein moves towards nucleus; kinesin moves away
• What is the viral strategy for protein production?

  • Translational shutoff: stops host translation
  • Hijacks translation complex for viral synthesis
• What are the functions of non-structural proteins produced in the early phase?

  Antagonize immune responses and enable replication
• What are the functions of structural proteins produced in the late phase?

  Assist in virus assembly and packaging
• How does protein production change over time during infection?

  • Early phase: focuses on non-structural proteins
  • Late phase: produces structural proteins
  • Protein levels peak during late phase
• What is the Flavivirus polyprotein model?

  • Genome encodes a single long polyprotein
  • Cleaved by proteases into functional proteins
• What is the Thogotovirus segmented protein model?

  • Genome comprised of multiple RNA segments
  • Each segment encodes a distinct viral protein

  
• What must viral genomes do to be functional?

  Make mRNA readable by host ribosomes
• What does the Baltimore classification categorize viruses by?

  • Genome type
  • Replication method
• What are the key genome types of DNA viruses?

  • dsDNA: Class I
  • ssDNA: Class II
  • dsDNA with gaps: Class II
• What are the key genome types of RNA viruses?

  • ssRNA(+): Class IV
  • ssRNA(-): Class V
  • dsRNA: Class III
  • retrovirus: Class VI
• What does dsRNA stand for?

  Double-stranded RNA
• Where does replication of dsRNA viruses occur?

  In the cell nucleus
• What enzyme is used in dsRNA replication?

  DNA-dependent RNA polymerase