Give information about the production of Genetically Engineered Insulin.

(N/A) Management of adult-onset diabetes is possible by taking insulin at regular time intervals.
Insulin used for diabetes was earlier extracted from the pancreas of slaughtered cattle and pigs.
Insulin from an animal source caused some patients to develop allergies or other types of reactions to the foreign protein.
$\Rightarrow$ Insulin consists of two short polypeptide chains: chain $A$ and chain $B$.
Chain $A$ and chain $B$ are linked together by disulphide bridges.
In mammals,including humans,insulin is synthesized as a pro-hormone which contains an extra stretch called the $C$-peptide.
This $C$-peptide is not present in the mature insulin and is removed during maturation into insulin.
The main challenge for the production of insulin using $rDNA$ techniques was getting insulin assembled into a mature form.
In $1983$,Eli Lilly,an American company,prepared two $DNA$ sequences corresponding to $A$ and $B$ chains of human insulin and introduced them into plasmids of $E. coli$ to produce insulin chains. Chains $A$ and $B$ were produced separately,extracted,and combined by creating disulfide bonds to form human insulin.