Why can genetically engineered bacteria produce human proteins?

Genetically engineered bacteria can produce human proteins because the genetic code is nearly universal across almost all living organisms, from bacteria to humans. This allows bacterial cellular machinery to interpret human DNA sequences and translate them into the corresponding amino acid chains.1

To achieve this, scientists use recombinant DNA technology. A specific human gene, such as the one for insulin or growth hormone, is spliced into a plasmid—a small, circular piece of bacterial DNA that replicates independently. Once this recombinant plasmid is introduced into a bacterial cell, the bacterium treats the human gene as its own, transcribing and translating it to synthesize the desired human protein. This process effectively turns bacteria into biological "factories" capable of manufacturing large quantities of valuable proteins for medical and research purposes.23