Each DNA fragment, which has been cleaved and separated from the rest of the genetic material, contains one or more genes.
Remember that each gene gives rise to a proteinSo as we study the gene we are studying the protein it encodes.
But what should we do to study the gene?
We must introduce it into the genetic material (DNA) of a host for mRNA gene transcription and protein translation to occur.
O host It is an organism that multiplies (reproduces) rapidly, such as bacteria. When bacteria reproduce by bipartition they transmit their genetic material to their "children", so if this material contains the study DNA fragment, we will soon have millions of bacteria with the gene.
O plasmid It is the circular genetic material not bound to the chromosome that is spread by the hyaloplasm of bacteria. It undergoes the same process as chromosomal DNA transcription and translation, and multiply with each cell division, passing a copy to each "daughter" cell.
Plasmid is removed from bacterial cells so that the study gene can be inserted and then replaced in the bacterium.
To better understand, let's know this process step by step (follow in the picture):
- Researchers want to study a human gene that produces a protein that is not known to function.
- Researchers “cut” (using restriction enzymes) from human DNA, the gene of interest.
- This DNA fragment containing the gene is multiplied by PCR to obtain multiple copies of the same fragment (or the same information).
- The same enzyme that cleaved the human DNA gene is used to cleave the bacterial plasmid. Remember that the DNA fragment, when cleaved, generates adhesive tips that are complementary to the plasmid if cleaved with the same enzyme.
- Then the cleaved plasmid is mixed with the DNA fragments (containing the gene) and an enzyme called ligase "glues" the fragments to the plasmid, producing the so-called plasmid. Recombinant DNA. That done, recombinant DNA is introduced into a host bacterium.
- THE host bacteria It is placed in a selective nutrient medium, only those with recombinant DNA grow into colonies. After many generations of bacteria, the product of gene expression, human proteins, is purified from bacteria (they are separated from bacterial proteins).
This method produces a large amount of human proteins thus enabling its study.