Recombinant DNA (rDNA) is DNA that has been made by genetic engineering, by joining together pieces of DNA from two or more different sources.
Genetic engineering is the extraction of a gene from one organism, or the manufacture of a gene, in order to place it in another organism in such a way that the recieving organism expresses the gene.
A gene wanted for genetic engineering may be obtained by:
- The gene may be identified in the donor organisms DNA and extracted using restriction enzymes.
- mRNA transcribed from the wanted gene may be extracted from the donor organism and converted to single-stranded complementary DNA (cDNA) by the enzyme reverse transcriptase. The single-stranded DNA is made double-stranded by DNA polymerase.
- The gene may be manufactured by using the triplet code, if the primay structure of the wanted protein is known.
Or restriction endonucleases are found in bacteria, where they break down the DNA of invading bacteriophage viruses and so restrict the vital multiplication.
- Each restriction enzyme binds to and cuts DNA at a specific target site.
- The target site is commonly between 4 and 6 base pairs long and is symmetrical (palindromic)
- The bacterium's own DNA is protected from attack by not having the target site, or by having it hidden by chemical markers.
- The two strands may be cut in the same place, leaving blunt ends e.g GTT and AAC
- Or cut in different places, leaving sticky ends of unpaired bases e.g. G and GATCC
Joining DNA to form rDNA…