HIV

Question 1

Describe the structure of HIV

Answer 1

• The outside of HIV is a lipid envelope with embedded attachment proteins.
• Inside the envelope, is a protein layer called the capsid which encloses two single strands of RNA and some enzymes, including reverse transcriptase.

Question 2

Explain how HIV replicates

Answer 2

• Attachment proteins on HIV bind to a protein called CD4. This protein is found on T-helper cells
• The protein capsid fuses with the cell-surface membrane on the T-helper cell. The RNA and enzymes of the HIV enter the T-helper cell
• The HIV reverse transcriptase converts HIV’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 to make new viral proteins and RNA
• 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 cell with a piece of the cell surface membrane surrounding them which forms their lipid envelope

Question 3

Explain how HIV causes the symptoms of AIDS

Answer 3

HIV causes the destruction of T-helper cells. When the number of these cells declines to a certain level, we consider AIDS to have developed. Without t-helper cells, both the humoral and cell mediated branches of the specific immune system cannot activate. The individual therefore becomes highly susceptible to disease and infection.