In the human body, insulin is made as a pro-hormone…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
In the human body, insulin is made as a pro-hormone.
- What extra part does the pro-hormone have that the mature hormone does not have?
- What joins chain A to chain B in the mature insulin?
- Why was it a challenge to make mature insulin in bacteria?
- How did the method of 1983 solve it?
Need a reminder? The key ideaShow
Recombinant DNA technology makes safe and effective drugs in large amounts. Human insulin has two short polypeptide chains, A and B, joined by disulphide bridges. In the body it is made as a pro-hormone, which has an extra stretch, the C peptide, that is removed when the hormone matures. In 1983 the company Eli Lilly made DNA for chain A and for chain B, put them into plasmids of E. coli, made the chains separately and joined them. One A chain and one B chain make one insulin molecule. A recombinant vaccine, such as the hepatitis B vaccine, can be made in yeast.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. (a) The C peptide, a stretch between the two chains. It is removed when the hormone matures.
Step 2. (b) Disulphide bridges.
Step 3. (c) The main challenge was to get the insulin assembled into its mature form. A bacterium cannot process the pro-hormone as a human cell does.
Step 4. (d) Two DNA sequences were made, one for chain A and one for chain B. They were put into plasmids of E. coli. The chains were made separately, extracted, and joined by creating disulphide bonds.
Answer: (a) the C peptide; (b) disulphide bridges; (c) assembling the mature form; (d) two chains made separately, then joined.
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