HIV

Question 1

What is the structure of a HIV particle?

Answer 1

1. the first layer is a lipid envelope which is embedded with attachment proteins
2. then there is a second layer called a matrix
3. inside the HIV particle there is a protein layer called a capsid that encloses two strands of RNA (HIV viral protein material) and enzymes
4. A specific enzyme is called reverse transcriptase which catalyses the production of DNA from RNA
5. The presence of reverse transcriptase causes HIV to be a retrovirus

Question 2

How does HIV replicate?

Answer 2

• HIV can not replicate itself but it instead uses its genetic material to instruct its host cells biochemical mechanisms to produce new HIV.

Question 3

What are the steps of HIV replication?

Answer 3

1. HIV enters the bloodstream and circulates around the body
2. The attachment proteins on HIV attach to receptors on T helper cells
3. The HIVs particles capsid then fuses with the cell membrane of the host cell, causing Viral Rna and enzymes to enter the TH cell
4. HIVs reverse transcriptase converts the viral RNA to DNA
5. The newly formed DNA then enters the TH cells nucleus
6. New viral proteins are then produced
7. New virus particles are then assembled and leave the cell.

Question 4

Why do HIV particles cause the symptoms of aids?

Answer 4

• Hiv specifically attacks TH cells with an infected person having as low as 200mm-3 in the blood
• Without the sufficient number of TH cells, the immune system can not stimulate B cells to produce antibodies or cytoxic T cells to destroy pathogens
• This means that memory cells and plasma cells may be destroyed or infected
• Therefore, the body is unable to undergo adequate immune responses and therefore there are many symptoms of aids

Question 5

How do antiboitics treat bacterial infections?

Answer 5

• Antibiotics prevent bacteria from making normal cell walls and inhibit certain enzymes required for synthesis and metabolic processes
• this weakens the walls of bacterial cells and makes them unable to withstand pressure so water enters naturally by osmosis and the cell dies

Question 6

Why are antibodies then ineffective at treating HIV?

Answer 6

• Viruses rely on host cells to carry out their metabolic processes and lack their own metabolic pathways and cell structures
• Viruses also have a protein coat, not murein unlike bacteria making antibodies ineffective

Question 7

What is an ELISA test?

Answer 7

• the enzyme linked immunosorbant body
• this allows you to see if a paitent has any antibodies to an antigen or an antigen to an antibody
• this can be used for medical diagnosis or for allergies

Question 8

Describe the indirect ELISA test.

Answer 8

• First antigens that we are testing for are bound to the bottom of the reaction vessel
• Then a blood sample from a paitent is added to the reaction vessel
• any specific antibodies in the blood plasma to the antigens on the bottom of the reaction vessel. These are primary antibodies
• Any antibodies that do not bind are washed out
• A second antibody with an enzyme attached is added to the reaction vessel. These are known as secondary antibodies
• these secondary antibodies bind to the primary antibodies and are complementary
• then the vessel is washed out again to remove any unbound secondary antibodies and prevent a false positive
• Finally, a solution with a substrate is added
• This reacts with the enzyme attached to the secondary antibodies. If there are any secondary antibodies present, a coloured product is formed and the reaction vessel changes colour

Question 9

What is direct ELISA tests?

Answer 9

• only a single complementary antibody is added to the reaction vessel
• the reaction has antigens from a paitents blood plasma in well plates
• the detection antibodies with an attached enzyme is added
• if there is antigen is present in the sample, there will be an antibody -antigen complex formed
• the well is then washed out to remove any unbound antibodies and the substrate to give a colour change