Virus pathogenicity & reproduction

• Viruses are inert outside of living cells, but when they are in a host cell they can replicate
• How can viruses be pathogenic?

  • cell lysis when they escape from cells to infect other cells/organisms (shedding)
  • cell transformation where they can trigger cells to become cancerous
  • suppress the immune system (e.g HIV)
• What is the lytic cycle?

  1. Virion attaches to the cell
  2. Viral nuclei acid injected into cell leaving protein coat outside
  3. Nucleic acid and capsid protein are synthesised using the host's metabolism and they assemble to make mature virus particles
  4. Cell lysis releases the viruses
  5. New virus particles bud from the cell surface
• What is the lysogenic cycle?

  Lytic cycle except cell lysis releases the viruses, and viral nucleic acid intergrates into the host cell chromosome

  Viral nucleic acid can remain there for many cell generationsn with no effect, they enter the lytic cycle at some time later
• Why are viruses described as the ultimate parasite?

  • they are inert outside of living cells
  • they reproduce inside living cells
• What is the lytic cycle?

  Viruses reproduce using the host's metabolism to copy their own nucleic acid and synthesise a new protein coat
• How are viruses released after reproduction in the lytic cycle?

  • lysis of host cell
  • budding: where they envelope from the host's cell membrane
• Some viruses are lysogenic. What does this mean?

  They integrate their nucleic acid into the host genome