a. The genetic code table shown in Fig. 8.2 on p. 256 applies both to humans and

Question

a. The genetic code table shown in Fig. 8.2 on p. 256 applies both to humans and E. coli. Suppose that you have purified a piece of DNA from the human genome containing the entire gene encoding the hormone insulin. You now transform this piece of DNA into E. coli. Why can’t E. coli cells containing the human insulin gene actually make insulin?

b. Pharmaceutical companies have actually been able to obtain E. coli cells that make human insulin; such insulin can be purified from the bacterial cells and used to treat diabetic patients. How were the pharmaceutical companies able to create such “bacterial factories” for making insulin? (i.e., what does E. coli require in order to transcribe and translate the human insulin gene?

Explanation / Answer

a. The piece of DNA from human into E.coli will have to be transcribed by the E.coli enzymes which totally are from different classification. The entire gene coding for the insulin gene will have both introns and exons, which is not present in the prokaryote E.coli. So the transcription and translation machinery of E.coli will not be able to produce the human insulin.

b. Pharmaceuticals companies employ the genetic engineering technology to efficiently produce insulin in E.coli by deleting the introns and cloning only the coding region of insulin into the E.coli which consists of exons. This coding region will be under the E.coli promoter which will produce the human insulin in adundant amounts.

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