human insulin was first commercially produced by the American company Eli Lilly in 1983 . They prepared two DNA sequences corresponding to the A and B chains of human insulin and introduced them into the plasmids of Escherichia coli to produce the insulin chains . These chains were produced separately, extracted, and combined by creating disulphide bonds to form functional human insulin . This biotechnological approach ensures the insulin is identical to the natural human molecule and does not induce unwanted immunological responses, unlike insulin previously extracted from slaughtered cattle or pigs . Mastering such applications is a high-priority strategy for medical aspirants, as approximately 95% of NEET Biology questions are derived directly from the NCERT textbooks .