1. Isolating the Human Insulin Gene:
* Identifying the Gene: Researchers first had to pinpoint the exact DNA sequence that codes for human insulin. This involved studying the human genome and understanding the structure of the insulin protein.
* Cloning the Gene: Once the gene was identified, they used techniques like restriction enzymes and plasmids to cut out the insulin gene from human DNA and insert it into a small, circular piece of DNA called a plasmid. This created a recombinant DNA molecule.
2. Choosing a Suitable Bacterial Host:
* E. coli as the Workhorse: The bacterium *Escherichia coli* (E. coli) was chosen as the host organism. It's a well-studied, easily manipulated, and quickly reproducing bacterium, making it ideal for large-scale production.
3. Inserting the Gene into Bacteria:
* Transformation: The recombinant plasmid containing the human insulin gene was introduced into E. coli cells. This process, called transformation, involved creating conditions where the bacteria would take up the plasmid.
4. Selecting for Transgenic Bacteria:
* Antibiotic Resistance: The plasmid often contained a gene for antibiotic resistance. This allowed researchers to easily identify bacteria that had successfully taken up the plasmid. They would grow the bacteria in the presence of the antibiotic, and only those bacteria with the plasmid would survive.
5. Expressing the Insulin Gene:
* Promoters and Regulation: The plasmid was designed so that the human insulin gene would be expressed (turned on) inside the E. coli. This involved including a promoter sequence – a DNA region that tells the bacterial machinery to start reading and transcribing the insulin gene.
6. Producing and Purifying Insulin:
* Large-Scale Fermentation: The transgenic E. coli bacteria were grown in large fermentation tanks, allowing them to produce large quantities of insulin.
* Purification: After fermentation, the insulin produced by the bacteria needed to be purified from the rest of the bacterial components. This involved various techniques like chromatography and filtration.
Important Note: This is a simplified overview. The process involved numerous technical details, iterations, and challenges, and many brilliant scientists contributed to its success.
