Final answer:
The A and B insulin chains are linked to β-galactosidase primarily to protect the chains from degradation and misfolding within E. coli bacteria, thus facilitating the production of functional, pure, and immune system-friendly human insulin.
Step-by-step explanation:
The human insulin used in treating diabetic patients is made in bacteria, and the A and B chains of insulin are linked to β-galactosidase mainly to prevent bacterial enzymes from degrading the insulin chains and to prevent misfolding of these chains. While the fusion to β-galactosidase helps in stabilizing the insulin chains in the bacterial host, it also assists in the purification process since the insulin chains can be cleaved from β-galactosidase and then properly folded to form functional insulin. This method of production ensures that the insulin is not only stable and active but also resembles human insulin closely enough to avoid immune reactions when administered to patients.
Manufacturing humulin, or synthetic human insulin, involves inserting artificially synthesized DNA sequences that code for the insulin A and B chains into the bacterial β-galactosidase gene. These recombinant DNA constructs are then introduced into E. coli cells, turning them into 'factories' that produce insulin as they grow and multiply. The expressed A and B chains are later extracted, purified, and combined to create insulin that replicates the structure and function of naturally produced human insulin.