How do scientists use recombitant dna to produce the drug insulin? why is it that genes from one organism can be expressed in another organism?

Recombinant DNA is a technology scientists developed that made it possible to insert a human gene into the genetic material of a common bacterium. This “recombinant” micro-organism could now produce the protein encoded by the human gene.
Scientists build the human insulin gene in the laboratory. Then they remove a loop of bacterial DNA known as a plasmid and…
insert the human insulin gene into the plasmid.
Researchers return the plasmid to the bacteria and…
put the “recombinant” bacteria in large fermentation tanks.
There, the recombinant bacteria use the gene to begin producing human insulin.
Scientists harvest the insulin from the bacteria and…
purify the substance for use as a medicine for people.

Genes can be moved between species. Because of the universality of the genetic code, the polymerases of one organism can accurately transcribe a gene from another organism in cases where it is impractical to test gene function using animal models, genes can first be expressed in bacteria or cell cultures.