viruses

• viruses

  • non cellular infectious particles
  • have a nucleic core(DNA or RNA so single or double stranded) and protein coat(capsid)
  • some have outer layer/capsid(envelope)- made of phospholipids
  • no cytoplasm or ribosomes
  • only reproduce in living cells- using their protein building machinery
• HIV transmission

  • sexual intercourse
  • blood donation
  • sharing needles
  • mother- child via placenta/birth milk
• replication of HIV

  virus infects T-helper cells, WBC responsible for activating antibody producing B cells

  1. glycoproteins on surface of virus binds to receptors on host cells membrane(t-helper)
  2. viral envelope fuses with cell membrane of T helper cell
  3. viral RNA enters, used as template by reverse transcriptase enzymes= complementary strand of DNA
  4. single RNA becomes double stranded DNA and inserted into host cell DNA
  5. uses host cell enzymes to produce viral components which form new virus - bud from host cells into blood stream, host cell dies
• aids

  • acquired immune deficiency syndrome
  • now unable to fight off infection
  • develops opportunistic diseases eg TB
  • symptoms of AIDS=weight loos, cancers, diarrhoea, opportunisitic disease