What Wockhardt did

  Recombinant human insulin is produced not in human cells but by using the human gene that has been inserted into some other cell. This other cell may be a bacterial or a yeast cell. While a variety of other cells may be used, these two host cells are preferred because they have been so extensively studied and so, as such, are known entities. Shown below is a much-simplified scheme of the procedure involved in developing recombinant human insulin.
The human cell is taken. And from the chromosome the relevant gene, in this case Insulin (red portion) is identified.
A suitable host cell is also identified. This may be a bacterial cell like E. coli or a yeast cell like S. cerevisiae. Both these cells have been used to produce insulin. Both the host cell and the human cell have the same genetic material namely DNA.
Specific enzymes are used to cut out the relevant portion of the genetic material, namely the insulin gene, which we require the product of. This gene is then put into the host cell.
The genetic material of the host cell is cut using another enzyme tool at a suitable place, leaving a gap where the insulin gene can be slotted.
The functional host cell produces insulin as one of the many proteins synthesised from its genetic material (green dots). This insulin is collected, purified and processed. The host cells are grown in large fermentation vats in huge quantities.