5.7 HIV

Question 1

How do HIV replicate ?

Answer 1

~HIV enters the bloodstream and circulates
~ HIV attachment protein (GP120) attaches to a receptor on the helper T-cell
membrane ( &laquo_space;GP120 binds with CD4 receptor protein)
~ Virus lipid envelope fuses with cell surface membrane and the capsid is released into cell which uncoats, releasing RNA and reverse transcriptase into cytoplasm
~HIV reverse transcriptase converts viral RNA into viral DNA
~the new viral DNA is integrated into host cell’s DNA (by enzyme integrase)
~ The Host cells enzymes are used to make viral proteins from viral DNA
~The viral proteins are assembled into new viruses which bud from the cell and go on to infect other cells
~ Eventually kills helper T cells, most host cells are infected and process repeat

Question 2

Describe the Structure of a HIV

Answer 2

~has a spherical structure, consisting of:
~an outer layer called a LIPID envelope
- embedded in the lipid envelope are loads of ATTACHMENT PROTEINS which help HIV attach to the host helper T-cell.
~ inside the lipid envelope is a protein layer called a CAPSID
~ inside the capsid there is 2 single strands of RNA and some enzymes/protiens
~ one of these proteins is reverse transcriptase which is needed for virus replication

Question 3

How does How HIV causes the symptoms of AIDS ?

Answer 3

HIV Infects and kills helper T cells (host cell) as it multiplies rapidly
- T helper cells then can’t stimulate cytotoxic T cells, B cells and phagocytes →
impaired immune response ( can’t perform immunity)
- poor immune system causes you to be More susceptible to infections.
- Diseases that wouldn’t cause serious problems in healthy immune system are deadly
(opportunistic infections) e.g. pneumonia

Question 4

What is the ELISA test used for ?

Answer 4

-Can determine if a patient has : -Antibodies to a certain antigen or
-any antigen to a certain antibody
-therefore it can be used to diagnose diseases or allergies (e.g. HIV / Lactose intolerance)

Question 5

Why use controls when performing the ELISA test?

Answer 5

Controls enable a comparison with the test To show that :
- Only the enzyme and nothing else causes colour change
- Washing is effective and all unbound antibody is washed away

Question 6

Explain why the secondary and detection antibody must be washed away

Answer 6

• Enzyme that is attached to the antibody reacts with substrate turning the solution a different
  colour; indicates a positive result
• Not washed out → enzymes will react with the substrate
• Therefore give a positive result even if no antigen present (false positive)

Question 7

Explain how the ELISA test is carried out

Answer 7

~ HIV antigen is bound to the bottom of a well or other sample surface
~a sample of patients blood plasma (containing different antibodies) is added to the well. If any HIV specific antibodies are present they will bind to the HIV antigen stuck to the bottom of the well
~ WASH OUT - to remove any unbound antibodies
~a secondary antibody that has a specific enzyme is attached to it is added to the well. The secondary antibody can bind to the primary antibody
~WASH OUT - to remove any unbound secondary antibodies
~a substrate containing solution is added to the well - this react with the enzyme attached to the secondary antibody and produces a coloured product
~ if the solution changes colour it indicates the patient has HIV specific antibodies and therefore is infected with HIV

Question 8

Explain why antibiotics are ineffective against viral diseases such as AIDS.

Answer 8

Antibiotics inhibit enzymes which weaken the murein cell wall causing them to burst under pressure. However viruses lack metabolic pathways and cell structures therefore there is no cell structures for them to disrupt. Viruses have a protein coat rather than murein cell wall so they do not have sites where antibodies can work