How is insulin made

A genetic engineering process


Many people suffer from diabetes, which is caused by a deficiency in the enzyme insulin. Before 1982, such people had to inject insulin obtained from pigs or cattle every day or even before every meal. These two types of insulin are similar to human insulin except for a few amino acids, but the differences are so great that the human immune system produces antibodies against pig or bovine insulin in some patients.

historical overview

In 1978 W. GILBERT succeeded in isolating an insulin gene from rats in bacteria of the species Escherichia coli In 1980 the same process was successfully carried out with the human insulin gene, and genetically engineered human insulin has been produced on a large scale since 1982.

Benefits of genetically engineered insulin

Genetically engineered human insulin has four main advantages over pig or beef insulin:

  1. Obtaining insulin is in principle easier, and larger quantities can be obtained at the same time.
  2. No antibody formation against the hormone, so no allergic reactions either.
  3. Very low risk of transmitting infectious diseases.
  4. Higher effectiveness as human insulin fits perfectly into the insulin receptors of the target cells.

Both the pharmaceutical industry (point 1) and patients (points 2 to 4) benefit from the genetic engineering of human insulin.

Basic principle of the genetic engineering process

I would now like to go into the basic principle of the genetic engineering process of insulin production. If you want to get bacteria to make human insulin, you have to inject the human insulin gene into bacteria so that the bacterial transcription and translation apparatus translates the gene into a functional insulin peptide.

For reasons of time and space, I do not want to go into the fundamental problems that one has when introducing eukaryotic DNA into prokaryotic cells and wanting to have it expressed. The introns contained in eukaryotic genes cannot be removed by the prokaryotic protein synthesis apparatus, and many eukaryotic proteins are still processed after transcription, i.e. changed in the Golgi apparatus and in the endoplasmic reticulum, which the bacterial cell cannot do either. That should be enough problem descriptions for the beginning.

Human insulin DNA is transferred into bacteria, which then make lots of human insulin.

In genetic engineering, so-called plasmids, as they also occur in nature, are used to introduce eukaryotic DNA into bacteria. Plasmids are circular small DNA molecules that give bacteria properties such as antibiotic resistance. The great thing about plasmids is that, firstly, they are easily taken up by bacterial cells and, secondly, they are artificial and custom-made. You can now buy many artificial plasmids on the Internet.

The genetic engineers now "only" have to open a bacterial plasmid, insert the human insulin DNA, close the plasmid again, and then smuggle it into bacterial cells. The bacteria then do the rest by themselves ...

Problems with genetically engineered insulin production

The "finished" insulin consists of two peptide chains linked by disulfide bridges.

As you can see on the picture, the "finished" insulin molecule consists of two peptide chains that are linked by disulfide bridges. However, immediately after translation, the "unfinished" insulin consists of a longer peptide. This longer peptide is then cut into three parts in the Golgi apparatus and in the endoplasmic reticulum. The two longer chains are then reconnected with the help of two disulfide bridges - and the insulin is ready.

Back to insulin. However, bacteria do not have a Golgi apparatus or an endoplasmic reticulum. The human insulin produced in bacteria could therefore not be converted into the finished form.

The solution to the problem that the genetic engineers came up with looks like this:

  • An artificial DNA is produced for each of the two chains.
  • The DNA for the A chain is built into a bacterial strain,
    the DNA for the B chain into a second strain of bacteria.
  • The A chains and the B chains are then synthesized separately.
  • The isolated A and B chains are then brought together by adding the
    Cysteine ​​building blocks of the chains react with each other, so that
    Form disulfide bridges.

Details of the genetic engineering of insulin

You can find the details on the subpages: