Structure and Lifecycle of HIV
HIV is an RNA virus that belongs to a subfamily of retrovirus called lentivirus. Retroviruses contain RNA (ribonucleic acid) as their basic genetic material. HIV is spherical in shape and is 0.1 microns in diameter (1/10,000 of a millimetre). The basic structures of the virus contain the viral envelope, the HIV matrix proteins and the viral core which consists 2000 copies of viral protein p24 (National Institute of Allergy and Infectious Diseases 2012).
Lifecycle of HIV
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- Binding and fusion: HIV infects cells that carry the CD4 receptors on their plasma membrane. CD4 receptors are present on the surface of T cells and macrophages. These receptors allow the virus to bind and enter the host’s cells.
- Reverse Transcription: After entering the cell by attaching itself to the outside of the cell via CD4 receptor, HIV uses a special enzyme called reverse transcriptase to convert the single-stranded RNA into the double-stranded DNA.
- Integration: The newly formed DNA then travels towards the cell’s nucleus. Another enzyme called “integrase” hides the virus DNA into the host cell's DNA. This integrated viral DNA is referred to as "proviral DNA.”
- Transcription: By using the RNA polymerase, the proviral DNA instructs the cell’s machinery to form copies of HIV genetic material, as well as to transcribe a new strand of viral RNA, messenger RNA (mRNA) which is used as a blueprint to make long chains of HIV proteins.
- Assembly: The long chains of HIV proteins are then cut into smaller pieces by a viral enzyme called protease. Once these smaller HIV proteins come together with copies of HIV’s RNA genetic material, a new virus particle has been assembled.
- Budding: The newly assembled virus pushes out (“buds”) of the host cell to infect other cells. Unlike other budding viruses, the resulting HIV does not look exactly like the initially infected cell, exhibiting a range of variation thus making it harder for the development of vaccines.