5.7 - HIV

• HIV


  human immunodeficiency virus

  A retrovirus which infects lymphocytes
• why is HIV a retrovirus

  it contains reverse transcriptase so can make DNA from RNA
• how is HIV transmitted

  sexually transmitted so via body fluids

  from HIV-positive mother to baby
• why does HIV cause life long disease

  inserts genetic Material into host cell genome
• how HIV affects the body

  infects t helper cells which act as a host so they can't trigger an effective immune response to antigens
• replication of HIV


  HIV enters bloostream & circulates around body

  attachment proteins bind to helper t-lymphocytes

  capsid fuses with call surface membrane & HIV RNA & enzymes enter helper t-lymphocyte

  reverse transcriptase makes complementary strand of DNA from viral RNA template & new DNA is inserted into cell's DNA

  HIV DNA in nucleus creates mRNA using cell's enzymes so new viral proteins are made

  mRNA leaves nucleus via nuclear pores & uses cell's protein synthesis mechanisms to make HIV particles

  HIV particles break away from t-cells with part of cell membrane to form lipid envelope
• AIDS


  acquire immunodeficiency syndrome
• how HIV leads to AIDS

  HIV kills/interferes with normal functioning of helper t-lymphocytes so there's less of them so immune system can't produce enough antibodies or memory lymphocytes so body can't produce effective immune response & becomes susceptible to other infections/disease
• number of t-lymphocytes in healthy person

  800-1200 per mm3 of blood
• number of t-lymphocytes in person with HIV

  200 per mm3 of blood
• initial symptoms of AIDS

  minor infections of mucous membranes

  recurring respiratory problems
• symptoms of AIDS as it progresses

  More susceptible to more serious infections

  chronic diarrhoea

  severe bacterial infections

  tuberculosis
• symptoms of AIDS in the later stages

  range of serious infections

  toxoplasmosis of the brain

  candidiasis of respiratory system
• antibiotics against bacteria


  kill bacteria by targeting bacterial enzymes & ribosomes used in metabolic reactions or by inhibiting enzymes needed for synthesis & assembly of cell walls so they are weakened so can't withstand pressure so more water enters by osmosis so cell bursts & bacterium dies
• antibiotics against viruses

  don't work because viruses don't have any metabolic mechanisms or structures to disrupt (they use host cell)

  viruses have a protein coat rather than murein cell wall so don't have anywhere antibiotics can work
• cure for HIV


  no cure or vaccine but antiviral drugs can be used to slow down progression of HIV and AIDS
• best way to control HIV infection

  by reducing its spread
• test for HIV


  ELISA test