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A gene holds the blueprint for a protein. By inserting a human gene into bacteria, scientists can harness bacterial metabolism to synthesize massive quantities of the encoded protein. Insulin, essential for patients with diabetes, is a prime example: recombinant human insulin is produced in engineered bacterial cultures, providing a safe and efficient supply for therapeutic use.
Bacteria carry plasmids—small circular DNA molecules—capable of accepting foreign DNA fragments. The human genome can be fragmented and inserted into plasmids, each of which is then cloned into bacterial cells. Each colony yields millions of identical bacteria containing a specific genomic segment, creating a cryogenic “library” where every vial stores a defined piece of human DNA.
Because bacterial growth is unaffected by mutations in the inserted gene, researchers can introduce precise changes—point mutations, deletions, or insertions—into the plasmid. The resulting mutant gene is expressed in bacteria, allowing rapid amplification of a diverse library of variants. These mutated genes can later be reintroduced into human cells to assess functional consequences.
Plasmids can be engineered to co‑express a reporter such as green fluorescent protein (GFP). By fusing the human protein of interest to GFP, scientists obtain a fluorescently labeled construct. After production in bacteria and isolation of plasmids, the fusion gene is delivered to human cells, enabling real‑time visualization of protein localization and dynamics under a fluorescence microscope.
