(7) HIV

• HIV causes the disease AIDS
• HIV = human immunodeficiency virus
• AIDS = acquired immune deficiency syndrome
• HIV was first diagnosed in 1981
• HIV is spread through advantage of bodily fluids
• HIV structure :

  • lipid envelope embedded by attachment proteins
  • inside is protein capsid
  • protein capsid contains viral genome + reverse transcriptase
• reverse transcriptase is an enzyme that catalyses the production of DNA from RNA
• HIV is called a retrovirus
• lipid envelope is stolen from the host cell
• attachment proteins in HIV are used :

  • to bind to receptors of the host cell + enter
  • can act as antigen
• Reverse Transcriptase :

  • transcribe viral RNA to produce DNA
  • viral DNA is what host cell transcribe and translate to produce proteins
• viruses can‘t replicate themselves - uses its genetic material to instruct the host cells biochemical mechanisms
• HIV uses host cells mechanisms to reproduce
• HIV replication :

  • HIV enters bloodstream and circulates around body
  • protein on HIV readily binds to protein (CD4) - HIV usually attaches to T helper cells (cell T)
  • protein capsid fuses with cell surface membrane - RNA and reverse transcriptase enter cell T
  • HIV reverse transcriptase convert viruse’s RNA into DNA
  • newly made DNA is moved into cell T nucleus - inserted into the cells DNA
  • HIV DNA in nucleus creates mRNA using cells enzymes
  • transcription + translation
  • HIV breaks away from cell T - takes a piece of cells cell surface membrane - forms lipid envelope
• once infected with HIV a person is said to be HIV positive
• replication of HIV often goes into dormancy and only recommences leading to AIDS, many years later
• HIV specifically targets helper T cells
• HIV causes AIDS by killing or interfering with the normal functioning of helper T cells
• an uninfected person has around 800-1200 helper T cells in each mm3 of blood
• helper T cells are important in cell-mediated immunity
• without a sufficient number of helper T cells the immune system can't :

  • stimulate B cells to produce antibodies
  • the cytotoxic T cells that kill cells infected by the pathogen
• HIV lies dormant
• AIDS is a syndrome = collection of different diseases
• HIV causes memory cells to be infected and destroyed
• As HIV affects memory cells, the body is unable to produce an adequate immune response and become susceptible to other infections and cancers
• AIDS = collection of diseases caused by a weak immune response
• With AIDS, it is the secondary infection that is the most dangerous and ultimately cause disease
• HIV does not kill individuals directly
• by affecting the immune system, HIV prevents it from functioning normally
• the ELISA test is a quantitative test as it accounts for concentration of antigen in bodily fluids
• ELISA = enzyme linked immunosorbent assay
• ELISA test uses antibodies to test for both the presence of proteins in a sample and the quantity
• ELISA test is extremely sensitive and so can detect very small amounts of a molecule
• ELISA Test :

  • apply the sample to a surface, ELISA slide, to which all the antigen in the sample will attach
  • wash the surface several times to remove any unattached antigens
  • add the antibody that is specific to the antigen we are trying to detect and leave the two to bind together
  • was the surface to remove excess antibody
  • add 2nd antibody that binds with the first antibody-2nd antibody has enzyme attached to it
  • add colourless substrate of the enzyme-enzyme acts on substance to change it into a coloured product
  • the amount of antigen present is relative to the intensity of the colour
• ELISA test can be used to detect :

  • HIV
  • Tuberculosis
  • hepatitis
• ELISA is useful where the quantity of an antigen needs to be measured
• ELISA test is useful in :

  • drugs
  • allergen testing
• ELISA test isn't just used for antigens of pathogens
• antibiotics are ineffective against viral diseases like AIDS
• • Antibiotics prevent bacteria from making normal cell walls
  • antibiotics like penicillin inhibit certain enzymes required for the synthesis and assembly of the peptide cross-linkages in bacteria cell walls