HIV Revision notes | A-Level Biology AQA

HIV

This lesson covers:

The structure of HIV
The stages of HIV replication
How HIV causes the symptoms of AIDS

HIV structure

The human immunodeficiency virus (HIV) is a virus that weakens the immune system.

The structure of this virus is shown in the diagram below.

Diagram showing the structure of the HIV virus including envelope, capsid, enzymes, attachment protein, and genetic material.

The virus contains the following components:

Genetic material - Two single strands of RNA.
Enzymes - One of these enzymes is reverse transcriptase, which allows the virus to convert RNA into DNA.
Capsid - A layer of protein molecules that surrounds and protects the genetic material.
Envelope - An outer layer made up of phospholipids.
Glycoproteins - Also known as attachment proteins or envelope proteins, these help the virus to bind to host cells.

HIV replication

As HIV is a virus, it cannot replicate itself and instead must use a host cell to produce new virus particles. HIV uses helper T cells as host cells, damaging the immune system of the infected individual.

Their replication process is outlined below:

Diagram showing HIV attaching to a receptor on a helper T cell.

Attachment proteins on the HIV attach to receptors on a helper T cell.

Diagram showing HIV replication with viral RNA entering a host cell.

HIV releases its RNA into the helper T cell.

Diagram showing the process of HIV replication including viral RNA, reverse transcriptase, and viral DNA.

Reverse transcriptase converts this RNA into DNA.

Diagram showing HIV replication process with viral DNA integrating into host cell.

The viral DNA is inserted into the helper T cell's genome.

Diagram showing HIV replication process inside a host cell with viral proteins.

The helper T cell's DNA is translated to make viral proteins.

Diagram showing HIV replication using a helper T cell as a host.

The proteins are used to assemble new HIV particles.

Illustration showing HIV virus attaching to a helper T cell to begin replication.

Fully assembled HIV particles leave the cell in order to infect other cells.

HIV and AIDS

HIV infection progresses through multiple stages that may ultimately lead to the development of AIDS (acquired immunodeficiency syndrome).

Stage 1 - Transmission

HIV is transmitted via direct contact with bodily fluids (e.g. blood or sexual fluids) from an infected individual.

Stage 2 - Acute infection

Once HIV enters the body, it rapidly replicates.
This causes flu-like symptoms for 2 to 4 weeks.

Stage 3 - Latency period

HIV replication drops to a low level for several years or decades.
During this time, the individual usually experiences few or no symptoms.
Antiretroviral therapy (ART) can prolong this stage for many years.

Stage 4 - AIDS Development

After some years, HIV reactivates and destroys helper T cells.
As the number of T cells in the body drops over time, the immune system begins to fail.
At this point, we classify the person as having 'AIDS'.

Individuals with AIDS have a higher likelihood of developing various serious infections, and eventually, an opportunistic infection (e.g., pneumonia) can lead to death. AIDS also increases the risk of developing cancers.

Treatment:

HIV/AIDS is currently incurable.
However, antiretroviral therapy (ART) can reduce viral replication to such low levels that most infected individuals don't experience any symptoms and can't transmit the virus.