viruses

• How viruses cause disease (biology only)

  They enter host cells and replicate inside of them. The host cells rupture, releasing new viruses.
• How viruses differ from other microorganisms e.g. bacteria, fungi (biology only)

  Viruses are not living organisms. They do not reproduce and can only replicate inside a host cell.
• Pathways for virus replication inside living cells (biology only)

  • Lytic pathway
  • Lysogenic pathway
• Lytic pathway (biology only)

  1. Virus binds to specific receptors on host cell

  2. Virus injects its DNA into host cell and replicates its DNA using host cell machinery

  3. New viral structures are produced and assembled

  4. Host cell ruptures, releasing new viruses
• Lysogenic pathway (biology only)

  1. Virus binds to specific receptors on host cell

  2. Viral DNA injected into host cell and becomes integrated into host cell genome

  3. Viral DNA replicates each time the host cell divides. However, the cell remains normal.

  4. Trigger causes the activation of viral DNA. It enters lytic pathway.
• describe hiv


  caused by human immunodefiency virus , spread by direct contact with bodily fluids e.g blood semen , breast milk

  destroys white blood cells and makes person more susceptible to other diseases , leads to aids
• how can the spread of hiv be reduced

  use of condoms and protected sex , needle exchange , screening blood for hiv , deterring infected mothers from breastfeeding
• describe chlamydia


  caused by chlamydia bacterium , spread through sexual contact or direct contact with infected genital fluids , can result in infertility
• how can the spread of chlamydia be reduced

  condoms , screening