Understanding HIV: AQA A-Level Biology Notes

Understanding HIV and Pathogen Defence

You'll encounter four main types of pathogenic organisms in your studies: bacteria, viruses, fungi, and plasmodium. When it comes to fighting infections that hide inside cells, your body relies on cytotoxic T-cells as the primary defence force.

Human immunodeficiency virus (HIV) causes acquired immune deficiency syndrome (AIDS) and has a unique structure that makes it particularly dangerous. The virus has a lipid envelope studded with GP120 proteins that latch onto CD4 receptors on immune cells. Inside this envelope sits a capsid containing two single RNA strands and crucial enzymes.

The two key enzymes are reverse transcriptase (which makes DNA from RNA) and integrase (which inserts viral DNA into your host cell's DNA). This sophisticated setup allows HIV to hijack your cells completely.

Quick Fact: Vaccines provide artificial active immunity, but HIV's constantly changing nature makes vaccine development incredibly challenging.

HIV Replication and Impact on Immunity

HIV replication follows a seven-step process that's absolutely devastating to your immune system. After the virus fuses with a host cell and enters, reverse transcription creates viral DNA that gets transported to the nucleus and integrated into your cell's own DNA.

The hijacked cell then produces new viral RNA and proteins, which assemble at the cell surface to form immature HIV particles. Finally, an enzyme called protease releases proteins that create mature, infectious HIV ready to attack more cells.

HIV specifically targets helper T-cells, either killing them or disrupting their normal function. With fewer helper T-cells in your blood, your immune system can't properly stimulate B-cells to produce antibodies, leaving you vulnerable to opportunistic infections and cancers.

Antibiotics are useless against HIV because viruses lack their own metabolic pathways and cell structures - there's simply nothing for antibiotics to disrupt. HIV is classified as a retrovirus because it carries RNA and those two crucial enzymes that allow it to reverse the normal flow of genetic information.

Remember: Understanding HIV's replication cycle helps explain why combination drug therapies target different stages of infection.