15.3: Recombinant DNA
Scientists create recombinant DNA by combining DNA from different sources—often, other species—in the laboratory. DNA cloning allows researchers to study specific genes by inserting them into easily manipulated cells, such as bacteria. Organisms that contain recombinant DNA are known as genetically modified organisms (GMOs). Recombinant DNA technology produces organisms with new genes that can benefit science, medicine, and agriculture.
How Do Scientists Create Recombinant DNA?
Creation of recombinant DNA involves inserting a gene of interest into a vector—a vehicle that carries foreign DNA into host cells for DNA replication and protein expression. The most commonly used cloning vectors are plasmids, small circular pieces of DNA that replicate independently from the host’s chromosomal DNA.
To create recombinant DNA, both the donor DNA, including the gene of interest, and the vector are cut at specific nucleotide sequences—called restriction sites—using restriction enzymes. The enzyme DNA ligase seals the sugar-phosphate backbone where the gene of interest and plasmid connect.
The result is a recombinant DNA molecule consisting of a vector with an integrated piece of donor DNA—called an insert. A scientist may then introduce this hybrid DNA molecule into a host organism—typically bacteria or yeast—where it easily and rapidly replicates. This creates many copies of the gene of interest, which is necessary for scientific research and other applications. The gene may also be transcribed and translated into the desired protein—such as human insulin—by using the host’s cellular machinery.
Creating recombinant DNA is an imperfect process, and errors often occur. For example, the vector may close without the insert or the insert may be incorrect (e.g., backward). Before using the recombinant DNA for further studies, researchers have to check for errors. Nucleotide sequencing can help identify bacteria colonies that carry plasmids with the correct insert.
Scientists Use Recombinant DNA to Study Genes and Proteins
Recombinant DNA technology is particularly advantageous when a scientist needs many copies of a gene of interest or a protein product. However, a scientist’s research may require an added level of complexity, such as the detection or purification of their desired protein. To achieve this objective, a researcher may attach a tag or reporter—proteins used to identify a gene product—to their desired protein to create a fusion gene, or chimeric gene.
Applications in Medicine and Agriculture
Scientists first used recombinant DNA technology to produce human insulin in bacteria, resulting in a treatment for diabetes. Since that initial discovery, researchers have generated other recombinant DNAs for therapeutic use. Recombinant bacteria make human growth hormone—a protein required for normal growth and development—to treat patients with growth hormone deficiency. Recombinant mammalian cells, derived from humans and hamsters, produce Factor VIII—a protein required for normal blood-clotting—to treat patients with hemophilia. Evidently, recombinant DNA technology is a powerful tool for the large-scale production of essential proteins.
Agricultural advances in recombinant DNA technology also impact human well-being. For example, corn farmers suffered substantial crop damage due to the pest European corn borer. In response, scientists isolated genes from a soil-dwelling bacterium—Bacillus thuringiensis (Bt)—to create genetically modified, pest-resistant corn. Bacillus thuringiensis naturally produces proteins that are toxic to certain insects but not humans, plants, or other animals. The introduction of pest-resistant Bt corn improved crop yields and decreased use of chemical pesticides. Such agricultural applications enhance the quality and quantity of the global food supply.