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.
 

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