Course 28.2Lesson 1 of 3
Insulin was once taken from cattle and pigs, and it sometimes caused an allergy. Bacteria now make human insulin, in two chains that are joined in the laboratory. This lesson follows the insulin molecule from the pro-hormone of the body to the product of the factory, and adds the recombinant vaccine.
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A person with diabetes cannot control the sugar in the blood. Many such people need insulin at regular times. Where does the insulin come from?
For many years it was taken from the pancreas of slaughtered cattle and pigs. It worked, but the insulin of an animal is a foreign protein for a human. Some patients developed an allergy or other reactions to it.
Recombinant DNA technology gave a better way. In the previous chapter you met the tools of this technology. Here we look at what they have made possible. NCERT says that the recombinant therapeutics, which are medicines made by recombinant DNA technology, bring two gains.
NCERT also states that about 30 recombinant therapeutics are approved for human use in the world, and that 12 of them are marketed in India.
Insulin is a small protein of two short polypeptide chains. They are chain A and chain B, and they are held together by disulphide bridges. A disulphide bridge is a bond between the sulphur atoms of two cysteine units.
In mammals, including humans, insulin is not made in this form. It is made as a pro-hormone. A pro-hormone is like a pro-enzyme: it must be processed before it becomes a mature, working hormone. The pro-hormone of insulin has an extra stretch, the C peptide, between the two chains. When the hormone matures, the C peptide is removed. It is not present in the mature insulin.
The main difficulty of making insulin by rDNA techniques was to get the insulin assembled into its mature form. A bacterium does not process a pro-hormone as a human cell does.
In 1983, the American company Eli Lilly prepared two DNA sequences. One matched chain A and the other matched chain B of human insulin. They were put into plasmids of E. coli. The bacteria made the chains separately. The chains were extracted and combined by creating disulphide bonds. The product was human insulin.
A few numbers help to see the size of the task. These are standard values of biochemistry books. NCERT does not print them. Chain A has 21 amino acids and chain B has 30. The whole pro-hormone has 86, of which the C peptide has 31. The rest are four amino acids at the two joins, which are removed too.
This part is not in the NEET syllabus, but A-Level and IB ask it: later factories made the whole pro-hormone in one bacterium or in yeast, and cut out the C peptide in the laboratory. NCERT describes the method of the two chains. NCERT gives 1983 for this work. Books also give 1982 as the year in which the first recombinant insulin was approved for use in the United States. In an Indian paper, use the year of NCERT.
The NEET syllabus also names vaccine production. A vaccine is a harmless form of a germ, or a part of it, that trains the immune system. You will study the immune system in the chapter on human health. Here is the biotechnology.
The gene for a protein of the germ, the antigen, is put into a host. The host makes the protein in large amounts. The vaccine has only this protein, and no whole germ, so it cannot cause the disease. NCERT's example is the hepatitis B vaccine, which is produced from yeast.
The program counts the insulin molecules that two cultures can make.
The next program uses the standard amino acid counts to work out the length of the DNA for each chain.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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