Question

Explain how insulin can be produced using recombinant DNA technology.

Answer 1

Hint: Insulin is a hormone that regulates blood glucose in the body. It needs to be externally supplied in case of diabetes in human beings. The hormone was initially obtained from animals but the demand was much higher than the supply. Hence, recombinant DNA technology was used to produce purer insulin in greater quantities.

Complete step by step answer:
- The first product developed by recombinant DNA technology was insulin. It is a peptide hormone produced by the beta cells of the pancreatic islets.
- The structure of the peptide is a dimer made of an A-chain and B-chain, that have 21 and 30 amino acid residues, respectively. They are linked together by two disulfide bonds.
- Insulin was initially extracted from the pancreas of animals like pigs, cattle, and horses, and injected into diabetic humans. Although animal insulin is similar to human insulin, there are differences in the sequences of the amino acid residues. This leads to rejection from the human’s antibodies and inflammation.
- In 1955, Sanger determined the sequence of insulin and concluded it was a protein. Further research led to the usage of recombinant DNA technology for the production of biologically synthesized insulin.

- In this technique, the mRNA encoding for insulin is isolated from the pancreatic cells. It is converted to DNA by reverse transcriptase enzyme. The DNA fragmented is then cloned into a bacterial plasmid that has been cleaved with restriction enzymes and ligated with the cDNA with DNA ligase. The cloned vector is then transformed into the appropriate cell. The cells are then grown on media on a large scale, thus producing insulin on a large scale.
- This produced insulin is called humulin.

Additional Information:
- Insulin cannot be consumed orally as it will break down in the digestive system. It is injected subcutaneously through daily or long term needles or insulin pens.
- The gene for insulin has also been expressed successfully in some plants like safflower for future large scale production.
- Insulin is not only the first protein to be produced by recombinant DNA technology but also the first protein whose amino acid was sequenced.
- The precursor of insulin is known as proinsulin.

Note:
- Insulin in the body is produced and stored as a hexamer and the active form is a monomer.
- Insulin was discovered when Banting and Best isolated a protein they called "isletin" from the Islets of Langerhans from a dog’s pancreas and injected it into diabetic dogs, in turn reducing the dog’s blood sugar.
- There are two types of diabetes.
- Diabetes mellitus and Diabetes insipidus.