HIV REPLICATION CYCLE, BRIEFLY EXPLAINED

The 'T' helper cells are the key mediators of immune function in your body, which have three receptors that helps the HIV to access the cell.

  • CD4 receptor

  • CCR5 receptor

  • CXCR4 receptor


When the HIV get in contact with the 'T' helper cell , the envelope glycoprotein GP120 on the surface of the HIV envelope interact with above three receptors. At first GP120 binds CD4 receptor causing conformational change, later then CCR5 and CXCR4 receptors pulls the HIV even closer to the cell. The stalk of the GP120 protein helps the virus to pierce through the cell membrane and pull it together. Fusion of this two membrane making an easy way for the virus to inject its genetic material [ viral capsid covering RNA and enzymes ] in to the cell. The cell detects the presence of viral capsid and starts to attack it with cellular enzyme, which causing the release of capsid material, consist of enzymes and RNA. HIV is unique from all other viruses because of the presence of REVERSE TRANSCRIPTASE enzyme on its viral RNA. This enzyme makes a strand of viral DNA; from viral RNA and 'Nucleotide [ from the 'T' cell ], then producing a complementary strand of DNA for the single strand DNA, result in production of VIRAL DNA.





There is also one more special enzyme present on the viral RNA called integrase, which brings the viral DNA [ produced by reverse transcriptase ] into the cell nucleus and make it fuse with human T cell DNA. From this integrated DNA a new viral mRNA is produced by DNA transcription enzyme, which then leaves the nucleus and finds the ribosomes on the rough endoplasmic reticulum. And here starts the production of envelope protein that cluster together on the cell wall. Ribosomes also producing viral polyprotein [consist of multiple different viral protein ] from the viral mRNA. Now all these components can come together to form a new immature HIV particle. Then a special enzyme called protease comes along and cleave up viral polyprotein. Now the viral material get separated from the T cell and it is ready to infect other cells.


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