Explain why it is not feasible to insert the entire human insulin gene into E. coli and anticipate the production of insulin.

Verified step by step guidance

1. Understand that the human insulin gene contains both exons (coding regions) and introns (non-coding regions). In humans, the gene is transcribed into pre-mRNA, which then undergoes splicing to remove introns, producing mature mRNA.
2. Recognize that E. coli, being a prokaryote, lacks the cellular machinery to perform RNA splicing. Therefore, if the entire human insulin gene (including introns) is inserted into E. coli, the bacterium cannot correctly process the gene to produce functional mRNA.
3. Note that without proper mRNA processing, the translation machinery in E. coli will produce a nonfunctional or truncated protein because the introns will be translated as well, disrupting the insulin protein sequence.
4. Conclude that to produce insulin in E. coli, scientists use complementary DNA (cDNA) synthesized from mature mRNA, which contains only the exons, ensuring that the bacterial system can translate the gene correctly into functional insulin protein.
5. Summarize that the key issue is the presence of introns in the human insulin gene and the inability of E. coli to process these introns, making direct insertion of the entire gene ineffective for insulin production.

Key Concepts

Gene Structure in Eukaryotes vs. Prokaryotes

Eukaryotic genes, like the human insulin gene, contain introns (non-coding regions) that are removed during RNA processing. Prokaryotes such as E. coli lack the machinery to splice out introns, so inserting the entire gene including introns prevents proper protein synthesis.

Use of cDNA for Gene Expression in Bacteria

To express eukaryotic proteins in bacteria, scientists use complementary DNA (cDNA) synthesized from mature mRNA, which lacks introns. This allows E. coli to transcribe and translate the gene correctly, producing functional insulin.

Post-Translational Modifications and Protein Folding

Human insulin requires specific folding and modifications to become active, processes that E. coli may not perform correctly. Even with the gene expressed, bacterial systems might produce inactive or misfolded insulin without additional engineering.