# Yunus GÖKDEMİR **Retro Viruses** ''Temel, Klinik ve Tanısal Tıbbi Viroloji by PROF. DR. MUSTAFA ALTINDİŞ''
Retroviruses in Group 6 of the Baltimore classification are enveloped, single-stranded, positive-sense RNA viruses and are called retroviruses thanks to the reverse transcriptase enzyme they have.
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Reverse transcriptase enzyme, which converts the RNA genome into a double-stranded DNA copy, enables integration into the host chromosome. The viral envelope formed from the host cell membrane contains the complex HIV protein that protrudes on the surface of the virus particle and is observed as spikes in electron micrographs of the virus.
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They have an icosahedral structure and contain gp41 gp120 lipid membrane RNA reverse cryptase.

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Like most enveloped viruses, all retroviruses are highly sensitive to factors that alter surface tension. Under normal conditions, they are not contagious through air, dust, formites. Contact with infected sources such as body fluids, blood and blood products is necessary for transmission.
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* The most known virus from the retrovirus family is the HIV virus, which causes AIDS.
* In short, AIDS disease destroys the CD4(+) T lymphocytes of the immune system, which has the task of preventing infections.
* HIV is a virus belonging to the retroviridae family. It is an enveloped positive-stranded RNA virus with a diameter of about 110 nm.
* The HIV RNA genome contains 3 large gene regions called gag, pol and env.
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> **This infographic illustrates the HIV replication cycle, which begins when HIV fuses with the surface of the host cell. A capsid containing the virus’s genome and proteins then enters the cell. The shell of the capsid disintegrates and the HIV protein called reverse transcriptase transcribes the viral RNA into DNA. The viral DNA is transported across the nucleus, where the HIV protein integrase integrates the HIV DNA into the host’s DNA. The host’s normal transcription machinery transcribes HIV DNA into multiple copies of new HIV RNA. Some of this RNA becomes the genome of a new virus, while the cell uses other copies of the RNA to make new HIV proteins. The new viral RNA and HIV proteins move to the surface of the cell, where a new, immature HIV forms. Finally, the virus is released from the cell, and the HIV protein called protease cleaves newly synthesized polyproteins to create a mature infectious virus.**
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# **Life Cycle of HIV**
* Binding (attachment)
HIV binds (attaches itself) to receptors on the surface of a CD4 cell.

* Fusion
The HIV enveloped and the CD4 cell membrane fuse (join together), which allows to enter CD4 cell.

* Reverse Transcription
Inside the 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).

* Integration
Inside the CD4 cell nucleus, HIV releases integrase (an HIV enzyme). HIV uses integrase to insert its viral DNA into the DNA of the CD4 cell.

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# **Life Cycle of HIV**
* Replication
Once integrated into the CD4 cell DNA, HIV begins to use the machinery of the CD4 cell to make long chains of HIV proteins. The protein chains are the building blocks for more HIV.

* Assembly
New HIV proteins and HIV RNA move to the surface of the cell and assemble into immature (noninfectious) HIV.

* Budding
Newly formed immature (noninfectious) HIV pushes itself out of the host CD4 cell. The newHIV releases protease (an HIV enzyme). Protease breaks up the long protein chains in the immature virüs, creating the mature (infectious) virus.
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