HIV: Structure, Transmission, and Replication

HIV Structure and Transmission

HIV, or Human Immunodeficiency Virus, is a retrovirus that cannot survive outside the human body. Its structure is complex, consisting of several key components that enable its infectious capabilities.

Highlight: HIV's structure includes two RNA strands, proteins (including reverse transcriptase), a protein capsid, and a viral envelope made of a lipid bilayer with glycoproteins.

The virus can be transmitted through various means, all involving the exchange of bodily fluids:

• Sexual intercourse
• Sharing of needles by intravenous drug users
• Mother-to-child transmission across the placenta or through breast milk
• Blood transfusions (though this is now rare due to screening)

Vocabulary: Retrovirus - A type of virus that uses RNA as its genetic material and requires reverse transcription to replicate.

HIV Replication Process

The replication of HIV within the human body is a multi-step process that targets helper T cells, a crucial component of the immune system.

1. Entry: HIV enters the bloodstream and infects helper T cells.
2. Reverse Transcription: Viral RNA is converted to DNA using reverse transcriptase.
3. Integration: The viral DNA is inserted into the host cell's chromosomes.
4. Latency: Infected cells remain normal as viral DNA is inactive.
5. Activation: After a period, viral DNA becomes active and takes control of the helper T cell.
6. Production: New HIV particles are produced, causing the host cell to die and release thousands of new viruses.

Example: During the latency period, an individual is HIV-positive and will have antibodies against the virus, but may not show symptoms of AIDS.

The gradual destruction of helper T cells impairs the immune system's ability to fight off infections:

• B cells are no longer activated, leading to reduced antibody production.
• The body's ability to combat infections decreases, eventually leading to AIDS.

Definition: AIDS (Acquired Immunodeficiency Syndrome) - The final stage of HIV infection, characterized by a severely weakened immune system.

Quote: "HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat."

This detailed understanding of HIV's structure, transmission, and replication is crucial for A Level Biology HIV exam questions and provides a foundation for comprehending the virus's impact on the human immune system.