• Created by: lee8444
  • Created on: 16-02-20 11:41

Structure of HIV

  • Has a lipid envelope on the outside
  • Peg-like attachment proteins embedded in the envelope
  • Inside the envelope is a capsid - protein layer
  • Inside the capsid is two single strands of RNA
  • Along with the RNA are some enzymes
  • One enzyme is reverse transcriptase. This catalyses the production of DNA from RNA. Due to this, HIV belongs to a group of viruses called retroviruses
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Replication of HIV

  • HIV enters the bloodstream and circulates around the body
  • A protein called CD4 is on many different human cells but HIV most frequently attaches to T helper cells
  • The capsid fuses with the cell-surface membrane
  • The RNA and enzymes of HIV enter the T helper cell
  • The reverse transcriptase converts HIV RNA into DNA
  • Newly-made DNA is inserted into the T cell's DNA
  • HIV DNA creates mRNA which contains instructions on how to make more of the enzymes needed for HIV production
  • Protein synthesis produces all of the proteins which make new HIV particles
  • HIV particles break away from the T cell using the T cell's cell-surface membrane as a lipid envelope
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How HIV causes AIDS

  • HIV specifically attacks T helper cells
  • HIV causes AIDS by killing or interfering with the normal function of T helper cells
  • An uninfected person has between 800 and 1200 helper T cells per mm cubed of blood
  • An infected person has less than 200 T cells per mm cubed of blood
  • T helper cells are important for cell-mediated immunity
  • Without enough T helper cells, the immune system cannot stimulate B cells to produce enough antibodies to deal with the infection
  • Memory cells can also become infected and destroyed so the secondary immune response is also impacted by AIDS
  • Many AIDS sufferers develop infections in the lungs, intestines, brain and eyes as well as experiencing weight loss and diarrhoea
  • It is the secondary diseases that ultimately lead to death
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The ELISA test

  • ELISA - enzyme-linked immunosorbent assay
  • Uses proteins to detect disease and also how prevalent the disease is within a sample
  • Apply the sample to a surface to which all of the antigens will attach
  • Wash the surface several times to remove any unattached antigens
  • Add the antibody that is specific to the antigen that we are trying to detect and leave them to bind together
  • Wash the surface to remove excess antibody
  • Add a second antibody that binds to the first antibody
  • This second antibody has an enzyme attached to it
  • Add the colourless substrate that is complementary to the enzyme to the slide
  • When the enzyme controlled reaction happens a colour is produced showing the presence of the disease and the amount of colour produced shows the intensity of the disease
  • Works for HIV, tuberculosis and hepatitis and it is especially useful when needing to find the quantity of the disease instead of just a positive or negative detection of a pathogen
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Why antibiotics are ineffective against viral dise

  • Antibiotics prevent bacteria from producing normal cell walls
  • In cells, Water constantly moves in by osmosis which doesn't cause the cell to burst because of the wall made of murein in bacteria which is tough and not easily stretched
  • Antibiotics like penicillin inhibit enzymes that are used to produce murein by stopping the creation of the peptide bonds
  • This weakens the walls making them unable to withstand the pressure caused by water entering the cells by osmosis
  • This causes the cell to burst
  • Viruses rely on host cells to carry out their metabolic pathways and produce cell structures
  • Antibiotics are therefore ineffective as there aren't any metabolic processes to stop or disrupt
  • When antibiotics are in cells the antibiotics cannot reach them
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