組換え型DNA

Recombinant DNA combines DNA from different sources, usually different species, in the laboratory. Scientists cut donor DNA and vector DNA using restriction endonucleases at specific sequences, then join them with DNA ligase. The resulting recombinant DNA is inserted into a host organism like bacteria or yeast, where it replicates to create many copies of the gene of interest for research and therapeutic applications.

Restriction endonucleases cleave DNA at particular nucleotide sequences called restriction sites on both the donor DNA and vector. DNA ligase then seals the sugar-phosphate backbone where the gene of interest and plasmid connect, joining them into a single recombinant DNA molecule. This two-step process ensures precise and stable combination of DNA from different sources.

A plasmid is a small circular piece of bacterial DNA that replicates independently from the host's chromosomal DNA. Plasmids serve as vectors, carrying foreign DNA into host cells for replication and protein expression. They are commonly used because they are easily manipulated, replicate rapidly in bacteria or yeast, and allow researchers to study specific genes by inserting them into these manageable organisms.

Scientists insert the human insulin gene into a plasmid vector and introduce it into bacterial host cells. The bacteria replicate the recombinant DNA and use their cellular machinery to transcribe and translate the gene into human insulin protein. This large-scale production method allows bacteria to manufacture therapeutic proteins like insulin for treating diabetes, growth hormone for growth deficiency, and Factor VIII for hemophilia.

Creating recombinant DNA is an imperfect process where errors often occur, such as vectors closing without inserts or inserts being inserted backward. Researchers use nucleotide sequencing to identify bacteria colonies that carry plasmids with the correct insert before using the recombinant DNA for further studies. This verification step is essential for ensuring accurate research results and therapeutic applications.

Scientists isolated genes from Bacillus thuringiensis, a soil bacterium that produces proteins toxic to certain insects but harmless to humans and plants. These genes were inserted into corn to create pest-resistant Bt corn, reducing crop damage from European corn borers. This agricultural application improved crop yields, decreased chemical pesticide use, and enhanced the quality and quantity of the global food supply.

Genetically modified organisms (GMOs) are organisms that contain recombinant DNA with new genes inserted through laboratory techniques. Recombinant DNA technology enables researchers to create GMOs in bacteria, yeast, plants, and mammalian cells for scientific research, medical treatment, and agricultural improvement. These organisms benefit science, medicine, and agriculture by producing essential proteins and pest-resistant crops at large scales.