AIDS: our research illness
The Human Immunodeficiency Virus
Replication cycle
The seven stages of the HIV life cycle are:
​
1.Binding (or Attachment): When HIV attacks a CD4 cell, the virus binds (attaches itself) to molecules on the surface of the CD4 cell: first a CD4 receptor and then either a CCR5 or CXCR4 coreceptor.
​
2. Fusion: After HIV attaches itself to a host CD4 cell, the HIV viral envelope fuses with the CD4 cell membrane. Fusion allows HIV to enter the CD4 cell. Once inside the CD4 cell, the virus releases HIV RNA and HIV enzymes, such as reverse transcriptase, protease and integrase.
​
3.Reverse transcription: Once inside a CD4 cell, HIV releases and uses reverse transcriptase (an HIV enzyme) to convert its genetic material—HIV RNA—into HIV DNA. The conversion of HIV RNA to HIV DNA allows HIV to enter the CD4 cell nucleus and combine with the cell’s genetic material—cell DNA.
4.Integration: Once inside the host CD4 cell nucleus, HIV releases integrase, an HIV enzyme. HIV uses integrase to insert (integrate) its viral DNA into the DNA of the host cell.
5.Replication: Once HIV is integrated into the host CD4 cell DNA, the virus begins to use the machinery of the CD4 cell to create long chains of HIV proteins. The protein chains are the building blocks for more HIV.
6.Assembly: During assembly, new HIV RNA and HIV proteins made by the host CD4 cell move to the surface of the cell and assemble into immature (noninfectious) HIV.
7.Budding: During budding, immature (noninfectious) HIV pushes itself out of the host CD4 cell. (Noninfectious HIV can't infect another CD4 cell.) Once outside the CD4 cell, the new HIV releases protease, an HIV enzyme. Protease acts to break up the long protein chains that form the noninfectious virus. The smaller HIV proteins combine to form mature, infectious HIV.
​
So that you can see the whole process, I have uploaded a video (spoken in catalan) in my YouTube profile, which, through a computer animation, shows you the whole life cycle of HIV:
