Reverse transcriptase is an enzyme found in retroviruses that can make DNA from RNA. When retroviruses infect a host, reverse transcriptase makes a copy of the virus’s RNA chromosome DNA, which is integrated into the host cell’s DNA. Reverse transcriptase has been used in genetic engineering to duplicate DNA, such as the genes for human insulin.
Reverse transcriptase is a type of enzyme found in a class of viruses called retroviruses, which include HIV, the hepatitis B virus, and some viruses that cause cancer. Retroviruses have RNA instead of DNA as their genetic code, and are capable of doing something most other cells are unable to do: they can reverse the process for transcription. In other words, they can make DNA from RNA. Reverse transcriptase, as the name suggests, is involved in this process.
In most cells, DNA carries genetic information. During transcription, DNA molecules are encoded into RNA molecules. These RNA molecules are then used in the cytoplasm of the cell to make proteins, during the translation process. Proteins determine what activities cells perform as they form enzymes and such molecules.
All viruses are parasites that live off their host cells. Most consist only of their genetic code, while some also contain an enzyme, such as retroviruses and reverse transcriptase. To reproduce, viruses must infect a host and then use the host’s cells to pass on their genes. There are several ways viruses can reproduce, including the use of reverse transcriptase by retroviruses.
When retroviruses infect a host, they often enter the host cell completely and lose their protective coat in the process. Once in the host cell, reverse transcriptase performs the process of reverse transcription, making a copy of the virus’s RNA chromosome DNA. This DNA is referred to as cDNA because it is a complementary DNA strand to RNA.
Once the cDNA is formed, the copy is integrated into the host cell’s DNA. Often the cDNA and the genes it contains become a permanent addition to the host’s DNA. The cDNA is now copied, transcribed, and translated with the rest of the DNA by host cell enzymes during normal DNA replication, transcription, and translation. In this way, the virus is able to create further copies of itself and its enzyme, which are then expelled from the cell and can further invade other cells.
Reverse transcriptase was discovered in 1970 and has played an important role in genetic engineering ever since. This enzyme has been isolated from viral cells and then used to make copies of DNA from different cells. An example of how reverse transcriptase has been used is to duplicate the DNA that codes for a particular protein in a particular organ: insulin is one example.
Diabetics were required to use horse or pig insulin for their injections. With the advent of genetic engineering, it is now possible to produce human insulin. First, the messenger RNA, or mRNA, that carries the instructions for insulin production is isolated from the insulin-producing cells of the pancreas. Reverse transcriptase is added to mRNA so that it can make copies of DNA or cDNA. The cDNA now carries the genes to make insulin and can be used to make large quantities for use by those who need it.
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