Q.Explain the mechanism by which HIV multiplies and leads to AIDS.

HIV is a retrovirus that infects and progressively destroys helper T-lymphocytes, crippling the immune system and causing AIDS.

Entry and infection:

HIV (Human Immunodeficiency Virus) enters the human body typically through sexual contact, transfusion of infected blood/blood products, sharing of infected needles, or from an infected mother to her child. Once inside, the virus specifically targets and enters macrophages and helper T-lymphocytes (TH cells, which bear the CD4 receptor that HIV's surface glycoproteins recognise and bind to).

Replication mechanism (retroviral cycle):

1. HIV's genetic material is single-stranded RNA (it is a retrovirus). On entering the host cell, the viral enzyme reverse transcriptase uses the viral RNA as a template to synthesise viral DNA.
2. This newly formed viral DNA gets incorporated (integrated) into the host cell's DNA (genome) with the help of the enzyme integrase.
3. The integrated viral DNA directs the infected host cell's machinery to produce new viral RNA and viral proteins (using the host cell's own transcription/translation machinery).
4. These components assemble into new HIV virus particles, which then bud off from the infected host cell (often destroying/killing the host cell in the process) and are released to infect other macrophages and helper T-cells.

Progression to AIDS: …