A culture of E. coli makes 80 million chains A of human insulin…
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A culture of E. coli makes million chains A of human insulin. A second culture makes million chains B. The chains are extracted and mixed, and they join one to one by disulphide bonds.
- How many million molecules of insulin can form?
- How many million chains are left over, and of which kind?
- A third culture makes more chains B, so that the two kinds are equal in number. How many million chains B must it add?
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.
Given. A chains: million. B chains: million.
Plan. One A and one B make one molecule, so count the pairs.
Step 1. Insulin. The smaller number is million, so million molecules form.
Step 2. Left over. million chains A are left. Chain B has none left.
Step 3. Equal numbers. To use all of the million chains A, we need million chains B, so another million chains B.
Answer: million molecules; million chains A left; million chains B to add.
Check. After the extra chains, million molecules form and nothing is left over.
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