Stories About Chemistry
57. The Longest Reaction
Hundreds and thousands of the most complex organic compounds have been made by chemists in their laboratories during recent years. Some of them are so complex that it is no easy thing even to write their structural formulas on paper. It requires quite a lot of time in any case.
The greatest victory scored by organic chemists is unquestionably the synthesis of a protein molecule, of the molecule of one of the most important proteins.
We are referring to the chemical synthesis of insulin, the hormone which controls carbohydrate metabolism in the organism.
If we tried to tell you about the constitution of the insulin molecule, it would take us several pages. Remember that some of the details of structure of this protein molecule are still not very clear even to specialists in chemistry. Insulin is a real giant molecule, though the number of elements contained in it is rather limited. But they are arranged in very elaborate combinations.
And so, for the sake of simplicity, let us assume that the insulin molecule consists of two parts, or rather, two chains - chain A and chain B. These chains are bound to one another by means of what is called a disulphide bond. In other words, they are bridged, as it were, by a crosslink consisting of two sulphur atoms.
The plan for the general attack on insulin was as follows. First, chains A and B were to be synthesized separately. Then they were to be connected with a disulphide crosslink between them.
Now for some arithmetic. To produce chain A, the chemists had to perform almost a hundred different consecutive reactions. Chain B required more than a hundred. And so all this took many months of very painstaking work.
But finally both chains were obtained. Now they had to be connected. And this is where the main difficulties sprang up. Disappointment followed upon disappointment.
Nevertheless, one fine evening there appeared in the laboratory log the laconic statement: “The synthesis of the insulin molecule is fully accomplished.”
Scientists had to go through two hundred and twenty three consecutive stages to obtain insulin artificially. Just think of that figure: hitherto not a single known chemical compound had been so difficult to prepare. It had taken ten men almost three years of incessant work to do it…
But biochemists report a very curious thing: in a living cell the synthesis of protein takes... from two to three seconds.
Three years, or three seconds! How far more perfect is the synthesis apparatus of the living cell than that of today’s chemistry!