Recombinant DNA means joining nucleic acids from different organisms (for example from human and bacteria). DNA recombination is a powerful tool that is being used in many different fields.

Isolating certain fragment of DNA is possible by dint of enzymes that cut the chain like biological scissors. High precision is ensured when using restriction endonucleases (they are obtained from bacteria) that cleave DNA at a specific sequence (for example first adenine in the sequence 5’-GAATTC-3’). Some of them cut two helices with a shift that makes so-called sticky endings. Such sticky ends can easily splice together.

It is also possible to synthesis DNA from nucleotides in laboratory.

Gene is introduced to genome of chosen organism by a vector. Viruses often act as vectors since their activity concentrates on incorporating their DNA in the host genome. It is the host that produces viral nucleic acids and proteins. Viruses can replicate only by infecting an organism.

Vectors are chosen depending on what kind of organism the gene should be carried into. If the object is a bacteria apart from infecting viruses called bacteriophages a plasmid can be used. Plasmid is circular piece of DNA that can be found in some of the bacteria. Usually they remain separate from bacterial “chromosome” but they often store information about useful traits such as resistance to an antibiotic.

DNA of the inserction and that of the vector cleaved with the same restriction enzymes easily splice together. Viruses introduce DNA by infection, plasmids are taken from the medium. When plasmids contain gene for resistance to an antibiotic it is easy to detect those that don’t have them. When adding an antibiotic those cells will be killed.

Once introduced to the genome the foreign DNA replicates with it and can undergo expression in the host.