Q.Describe the structure of the Human Immunodeficiency Virus (HIV) and explain, step by step, how it replicates inside a helper T-lymphocyte to eventually cause AIDS.

Structure of HIV: HIV is a retrovirus, meaning its genetic material is RNA rather than DNA. It consists of an outer envelope studded with glycoprotein spikes, which allow the virus to recognise and bind to specific target cells, surrounding an inner protein core. This core encloses two copies of the virus's single-stranded RNA genome along with its own reverse transcriptase enzyme, which the virus needs because host human cells have no natural way to copy RNA back into DNA.

Replication cycle inside a helper T-lymphocyte:

1. Attachment and entry: the glycoprotein spikes on HIV's envelope bind to receptors on the surface of a helper T-lymphocyte (CD4+ T-cell), allowing the virus to enter the cell.
2. Reverse transcription: once inside, the virus's reverse transcriptase enzyme converts its single-stranded RNA genome into double-stranded DNA.
3. Integration: this newly made viral DNA is transported into the cell's nucleus and integrated into the host cell's own DNA, effectively becoming a permanent part of the infected cell's genetic material.
4. Production of new viral components: using the host cell's own machinery, the integrated viral DNA directs the production of new viral RNA and viral proteins.
5. Assembly and budding: these newly made components assemble into new virus particles, which bud out from the surface of the host cell — a process that damages and can ultimately destroy the helper T-cell — and go on to infect further helper T-cells, repeating the cycle. …

Number the replication cycle as discrete steps (attachment, reverse transcription, integration, production, budding) — this is exactly the kind of process question where a clearl …

Do not describe HIV as directly 'attacking the immune system' in vague terms — the precise, examinable mechanism is that it infects and destroys helper T-lymphocytes specificall …