5.7 The human immunodeficiency virus (HIV)

Question 1

What does HIV cause

Answer 1

Acquired immune deficiency syndrome (AIDS)

Question 2

Describe the structure of HIV

Answer 2

Outside is a lipid envelope, embedded in which are peg like attachment proteins. Inside the envelope is a protein layer called the capsid that encloses two single strands of RNA and some enzymes. One of these enzymes is reverse transcriptase which catalyses the production of DNA from RNA.

Question 3

What does the presence of reverse transcriptase make HIV

Answer 3

A virus known as retroviruses

Question 4

How does HIV replicate itself

Answer 4

1. Following infection, HIV enters the bloodstream and circulates around the body
2. A protein on the HIV readily binds to a protein called CD4, this is usually on helper T cells
3. The protein capsid fuses with the cell-surface membrane. The enzymes and RNA of HIV enter the helper-T cell
4. The HIV reverse transcriptase converts the virus’s RNA into DNA
5. The newly made DNA is inserted into the helper T cells nucleus where it is inserted into the cells DNA
6. The HIV DNA in the nucleus creates mRNA using the cells enzymes. the mRNA contains the instructions for making new viral proteins and the RNA to go into the new HIV
7. The mRNA passes out of the nucleus through a nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles
8. The HIV particles break away from the helper T cell with a piece of its cell surface membrane surrounding them which forms the lipid envelope.

Question 5

How does HIV cause AIDS

Answer 5

The HIV specifically attacks helper T cells. HIV causes AIDS by killing helper T cells. The body slowly cannot produce an adequate immune response and becomes susceptible to other infections

Question 6

What is the process of the ELISA test

Answer 6

1. Apply the sample to a surface, for example a slide, to which all the antigens in a sample will attach
2. Wash the surface several times to remove any unattached antigens
3. Add the antibody that is specific to the antigen we are trying to detect and leave the two to bind together
4. Wash the surface to remove excess antibody
5. Add a second antibody that binds with the first antibody. This second antibody has an enzyme attached to it
6. Add the colourless substrate of the enzyme. The enzyme acts on the substrate to change it into a coloured product
7. The amount of the antigen present is relative to the intensity of colour that develops.