HIV and AIDS

• HIV structure

  A) Lipid envelope

  B) capsid

  C) reverse transcriptase

  D) RNA

  E) attachment proteins

  
• • capsid - encloses two single strands of RNA and some enzyme
  • Reverse transcriptase - enzyme catalyses the production of DNA from RNA, reverse reaction to this is carried out by transcriptase, presence of reverse transcriptase and consequent ability to make DNA from RNA, means HIV belongs to a group called retroviruses.
• Replication of HIV until new DNA synthesised

  1. Following infection, HIV enters the bloodstream and circulates around the body.
  2. A protein on HIV readily binds to a protein called CD4, HIV most frequently attaches to T helper cells.
  3. Protein capsid fuses with the cell surface membrane. RNA and enzymes of HIV enter the helper T cell.
  4. HIV reverse transcriptase converts virus RNA to DNA
• After DNA synthesis, replication of HIV

  1. Newly made DNA is moved into helper T cells nucleus where is is inserted into the cells DNA.
  2. The HIV DNA in the nucleus creates messenger RNA  (mRNA) using the cells enzymes. The mRNA contains instructions to make new viral proteins and the RNA goes into the new HIV
  3. The mRNA passes out of the nucleus through a nuclear pore and uses cell protein synthesis mechanisms to make HIV particles.
  4. HIV particles break away from the helper T cell with a piece of its cell surface membrane surrounding them which forms the lipid envelope.
• How HIV causes symptoms of AIDS:

  • HIV causes aids by killing or interfering with the normal functioning of helper T cells. An uninfected person normally has between 800-1200 helper T cells in each mm of blood. Someone suffering from AIDS the number can be as low as 200.
• PROBLEMS WITH A LACK OF HELPER T CELLS and memory cells

  • Without a sufficient number of helper T cells, the immune system cannot stimulate B cells to produce antibodies or cytotoxic T cells that kill cells infected by pathogens. 
  • Memory cells may be infected or destroyed, as a result the body is unable to produce an adequate immune response and become susceptible to other infections or cancers
• AIDS

  • Develops infections of lungs, intestines, brain and eyes, weight loss. It is these secondary diseases that ultimately cause death
  • HIV doesn't kill individuals directly, by infecting the immune system, HIV prevents it from functioning normally. So those HIV positive are unable to respond effectively to other pathogens, it is these infections that cause ill health and death.
• The ELISA test:

  • Stands for enzyme linked immunosorbent assay, uses antibodies to detect and identify quantity of protein in a sample.
• ELISA test

  1. Apply sample to a surface, a slide, to which all the antigens in sample will attach
  2. Wash the surface several times to remove any unattached antigens.
  3. Add the antibody that is specific to antigen we are trying to detect and leave two to bind together
  4. Wash the surface to remove excess antibodies.
  5. Add a second antibody that binds with the first antibody, the second antibody has an enzyme attached to it.
  6. Add colourless substrate of enzyme, enzyme acts on substrate ri change into a coloured product.
  7. Amount of antigen present relative to intensity of colour is developed.
• Why are antibiotics ineffective against viral diseases like AIDS?

  • Viruses rely on host cells to carry out their metabolic activities and therefore lack their own metabolic pathways and cell structures.
  • So antibiotics are ineffective as there are no metabolic mechanisms of cell structures for them to disrupt. 
  • Viruses have a protein coat rather than a murein cell wall so do not have sites where antibodies can work.
  • Viruses are within an organism's own cells so antibiotics cannot reach them.
• How do antibiotics work on bacteria?

  • Antibiotics like penicillin inhibit enzymes required for synthesis and assembly of peptide cross linkages in bacterial cell walls.
  • This weakens the walls, making them unable to withstand pressure of osmosis, as water enters by osmosis the cell bursts and bacteria dies.