1. HIV

2. What you must know.
Structure of the human immunodeficiency virus (HIV) and its replication in helper T cells.
How HIV causes the symptoms of AIDS. Why antibiotics are ineffective against viruses.
The use of antibodies in the ELISA test.

3. Structure of HIV
Attachment proteins

4. Helper cells.

5. Reverse transcriptase.
The genetic material in HIV is RNA.
It uses reverse transcriptase and is called a retrovirus.
This is an enzyme which takes the viral RNA and copies it to make DNA.
In this way the virus can insert DNA made from its RNA into the human genome.
Complete the DNA sequence:
RNA sequence : C G A A U G
DNA sequence:

6. Use this diagram and your prior knowledge to describe how the HIV virus reproduces.
( 4 marks).
step –through of HIV infection.

7. Answer:
1. Virus attaches: Proteins on the HIV virus "dock" with CD4 receptors on the target cell.
2. Genes copied: The HIV RNA is converted into DNA using the viruses reverse transcriptase.
3. Replication: The virus inserts this copy into the host cell’s DNA. The HIV DNA in the nucleus creates mRNA, so the cell synthesizes these proteins.
4. Release: The parts are assembled and form a "bud“ using the T cells membrane which breaks off to become a new HIV virus.

8. Artificially coloured purple HIV on the surface of a pink Helper-T cell.

9. They “bud” out of the host cell taking host lipids from the host membrane as a viral coat.
How does this help to protect them?
They kill the cell as they leave.

10. Infected T-helper cells can be killed by T-killer cells.
This together with the T-helpers being destroyed when the virus leaves, drastically reduces the T-helper cells available.
What is the knock-on effect of the loss of T-helper cells to the rest of the immune system?

11. The loss of T-helpers means that
Memory cells can be infected and destroyed
B-cells are not stimulated to produce antibodies
Cytotoxic T cells are not stimulated
The person’s immune system will be
seriously impaired.

13. The ELISA Test Enzyme-linked immunosorbant assay
Complete the steps of ELISA test