5.7 - Human immunodeficiency virus (HIV)

Question 1

How is HIV transmitted

Answer 1

• HIV is a retrovirus
• not transmitted by a vector
• HIV is unable to survive outside the human body
• the virus is spread by intimate human contact and can only be transmitted by direct exchange of body fluids

Question 2

describe how HIV replicates itself

Answer 2

• Following infection, HIV enters the bloodstream and circulates around the body
• A protein on the HIV readily bonds to a protein called CD4. While this protein occurs on a number of different cells. HIV most frequently attaches to T-helper cells
• the protein capsid fuses with the CSM. The RNA and enzymes of HIV enter the T-helper cells
• The HIV reverse transcriptase converts the virus’s RNA into DNA
• the newly made DNA is moved into the T-helper cell’s nucleus where it is inserted into the cell’s DNA
• the HIV DNA in the nucleus creates mRNA using the cell’s enzymes. This mRNA contains the instructions for making new viral proteins and the RNA to go into the new HIV
• the mRNA passes out of the nucleus through a nuclear pore and uses the cell’s protein synthesis mechanisms to make HIV particles
• The HIV particles break away from the T-helper cells with a piece of its CSM surrounding them which forms their lipid envelope

Question 3

What are the key components of HIV

Answer 3

• 2 RNA strands
• proteins (including reverse transcriptase)
• a protein coat (capsid)
• A viral envelope consisting of a lipid bilayer and glycoproteins (the lipid bilayer is derived from the cell membrane of host t-helper cells that the particle escaped from
• attachment proteins

Question 4

What does HIV stand for

Answer 4

The human immunodeficiency virus

Question 5

How does HIV cause the symptoms of AIDS

Answer 5

• causes AIDS by killing/interfering with the normal functioning of T-helper cells
• Normally you have between 800-1200 helper cells in each mm^3 of blood, but a HIV person has around 200 mm^3
• T helper cells are important in cell mediated immunity
• without them, immune system can’t:
  1) stimulate B cells to produce antibodies
  2) stimulate cytotoxic T cells that destroys cells infected by pathogens
  3) memory cells may also become infected and destroyed
• Therefore = body can’t produce an adequate immune response = becomes susceptible to infections and cancer
• the secondary diseases that ultimately cause death

Question 6

Does HIV directly kill individuals

Answer 6

• no
• by infecting the immune system = HIV prevents it from functioning normally
• as a result, those infected = unable to respond effectively to other pathogens
• it is these infections that then ultimately cause ill health and eventual death

Question 7

What does the ELISA test stand for

Answer 7

Enzyme linked immunosorbant assay

Question 8

What does the ELISA test detect

Answer 8

• detects the presence of a protein in a sample as well as quantity
• it’s extremely sensitive = can detect very small amounts of a molecule

Question 9

How does the procedure of an ELISA test go

Answer 9

• Apply the sample to a surface, e.g. a slide to which all antigens in the sample will attach
• wash the surface several times to remove any unattached antigens
• add the antibody that’s specific to the antigen we are trying to detect and leave the 2 to bind together
• wash the surface to remove excess antibody
• add a second antibody that binds with the first antibody. This secondary antibody has an enzyme attached to it
• add the colourless substrate of the enzyme. The enzyme acts on the substrate to change it into a coloured product
• the amount of the antigen present is relative to the intensity of colour that develops

Question 10

What diseases can an ELISA test be used to detect

Answer 10

• HIV
• Tuberculosis
• hepatitis
  Also..
• drug and allergy testing

Question 11

Describe the importance of the cell wall to bacteria

Answer 11

• in bacteria cells = water constantly enters by osmosis = cell expands and pushes against cell wall
• it doesn’t cause the cell to burst due to the murein cell wall (its a tough material that’s not easily stretched)
• because its relatively inelastic = cell wall resists the expansion and so halts further entry of water

Question 12

Describe what antibiotics do to bacteria

Answer 12

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

Question 13

Why are antibiotics ineffective against viral diseases like AIDS

Answer 13

• viruses rely on the host cells to carry out their metabolic activities and therefore lack their own metabolic pathways and cell structures
• as a result antibiotics are ineffective because there are no metabolic mechanisms or cell structures for them to disrupt
• Viruses also have a protein coat rather than a murein cell wall and so don’t have sites where antibiotics can work
• also, when viruses are within an organism’s own cells, antibiotics cannot reach them

Question 14

Answer 14