What is a retrovirus?

Shared via Quora

Answer by Patrick Reilly:

A retrovirus is an RNA virus (that is, an envelope around a protein capsid with RNA and some enzymes inside) with a reverse transcriptase (RT), which incorporates an RNA-dependent DNA polymerase and a DNA-dependent DNA polymerase, along with an integrase to stick the cDNA into the host’s DNA[1].

What does this mean?  Well, there are a few stages of infection with this type of virus.

  1. The protein capsid attaches to the host cell and injects the RNA and enzymes within the capsid into the host cell.
  2. The RNA-dependent DNA polymerase of the RT generates a single DNA strand complementary to the RNA the capsid injected.
  3. The DNA-dependent DNA polymerase then generates the second strand to that single DNA strand, producing dsDNA ready for incorporation into the host’s DNA.
  4. The integrase takes care of placing the viral dsDNA into the host’s DNA.  The RNA in a retrovirus typically codes for the protein capsule, RT, and the RNA it carries (not necessarily all on one strand).
  5. The host cell will eventually transcribe the region where the virus inserted it’s dsDNA, and when this happens, a bunch of new retroviruses are formed.
  6. These new viruses cause cell lysis (breaking the cell membrane, essentially like a microscopic explosion of a water balloon), which releases the new retroviruses out to infect more host cells.

About 9% (this is one estimate, others say 5-8%) of the human genome is thought to be viral DNA, likely from retroviruses that did not get transcribed out to kill the cell before reproduction.  This gives you an idea of how prevalent retroviruses are and were historically.

As Emad William mentions, the incorporation of the viral dsDNA into the host genome makes treating retroviruses very difficult.  However, the main problem with treating retroviral infections is not fixing infected cells, but preventing proliferation (the infection of other cells).

The human body is designed to replace most types of cells readily (we shed skin constantly, and turnover is a well-defined process), so the best way to fight viruses is to block them from entering more cells.  Certain viruses make this incredibly difficult (HIV being one of them) because they mutate their protein capsid and/or glycoproteins on the viral envelope to stay unrecognized by immunoglobulins.
Immunoglobulins are special molecules that attach to “antigens” such as certain proteins on the outer surface of viral envelopes or on the cell membrane of bacteria.

Yes, I know Wikipedia is an ugly reference, but do you have any virology books sitting at home?  Not everyone does.
[1]Reverse transcriptase

What is a retrovirus?


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