How does the production of human insulin in bacteria demonstrate the universality of the genetic code and enable gene transfer between species?

Sourav PanNovember 8, 2024

Answered

The production of human insulin in bacteria exemplifies the universality of the genetic code and demonstrates how gene transfer between species can be achieved. This process involves several key steps that highlight the compatibility of genetic information across different organisms.

Universality of the Genetic Code

1. Common Codon Usage: The genetic code is nearly universal, meaning that the same codons specify the same amino acids in almost all living organisms, from bacteria to humans. For instance, the codon AUG codes for methionine in both humans and Escherichia coli (E. coli) . This universality allows scientists to take genes from one species and express them in another, such as inserting the human insulin gene into bacterial DNA.
2. Gene Transfer Mechanism: The process begins with isolating the gene responsible for producing human insulin. This gene is then spliced into a plasmid vector, which is a small circular DNA molecule that can replicate independently within a bacterial cell . The plasmid is designed to include necessary elements for replication and expression in the bacterial host, such as promoters and antibiotic resistance genes .

Steps in Producing Human Insulin in Bacteria

1. Isolation and Cloning:
   • The human insulin gene is amplified using techniques like polymerase chain reaction (PCR) or reverse transcription from mRNA to create complementary DNA (cDNA), which lacks introns .
   • The insulin gene is then inserted into a plasmid vector using restriction enzymes to create “sticky ends” that allow for precise ligation of the gene into the plasmid .
2. Transformation:
   • The recombinant plasmid containing the human insulin gene is introduced into E. coli through a process called transformation. This can be accomplished using heat shock or electroporation methods, which make bacterial cell membranes permeable to DNA .
   • Once inside, the plasmid replicates within the bacterial cells, allowing multiple copies of the insulin gene to be produced .
3. Selection and Cultivation:
   • Transformed bacteria are cultured in fermentation tanks under controlled conditions. The presence of an antibiotic in the growth medium selects for only those bacteria that have successfully incorporated the plasmid (which carries an antibiotic resistance gene) .
   • As these bacteria grow and divide, they express the human insulin gene, synthesizing insulin as a polypeptide precursor .
4. Harvesting and Purification:
   • After sufficient growth, the bacterial culture is harvested. The insulin produced may initially exist as inclusion bodies, which require solubilization and refolding to yield biologically active insulin .
   • The final product is purified and processed for medical use, providing a reliable supply of insulin for diabetic patients .

Implications

The ability to produce human insulin in bacteria not only demonstrates the universality of the genetic code but also showcases how genetic engineering enables significant advancements in biotechnology and medicine. By transferring genes between species, researchers can create transgenic organisms capable of producing valuable proteins, such as hormones or enzymes, that may be difficult or inefficient to obtain from their natural sources.