1. Production of insulin by recombinant DNA technology started in the late 1970s.
2. This technique involved the insertion of human insulin gene on the plasmids of E. coli.
3. The polypeptide chains are synthesized as a precursor called pre-pro insulin, which contains A and B segments linked by a third chain (C) and preceded by a leader sequence.
4. The leader sequence is removed after translation and the C chain is excised, leaving the A and B polypeptide chains.
5. Insulin was the first eyer pharmaceutical product of recombinant DNA technology administered to human. In 1986 human insulin was marketed under the trade name humulin.

(i) Polymerase chain Reaction
(ii) In this process, multiple copies of the gene/ DNA of interest are synthesized in vitro using two sets of primers.
(iii) Primers are the chemically synthesized obligonucleotides that are complementory to the regions of DNA strands, where they will be annelated
(iv) The two strands of DNA have been separated by denaturation.
(v) The enzyme DNA polymerase extends the primers using the nucleotides provided in the medium on the genomic DNA as template.
(vi) To achieve repeated amplification, a thermostable DNA polymerase, called Taq polymerase obtained from Thermus aquaticus is used; it can withstand the high temperature used for the denaturation of DNA.

(i) Two sets of primers and the enzyme DNA polymerase are required in each cycle of  Polymerase chain reaction.
(ii) Role of primers and DNA polymerase Primers are necessary to start the functioning of DNA polymerase.
1. DNA polymerase extends the primers using the nucleotides provided in the reaction and the genomic DNA as the template.
2. The segments of DNA can be amplified to approximately billion times.
(iii) DNA polymerase used in PCR reaction is known as Tag polymerase, which is obtained from a bacterium Thermus aquaticus.

1. The human insulin is synthesized by the \(\beta\) cells of Islets of Langerhans in the pancreas. It is formed of 51 amino acids which are arranged in two polypeptide chains, A and B. The polypeptide chain A has 21 amino acids while the polypeptide chain B has 30 amino acids.
2. In the early years, insulin isolated and purified from the pancreas of pigs and cows was used to treat diabetic patients. Due to minor differences in the structure of the animal Insulin as compared allergic reactions in some diabetic patients.

1. In 1997, Rosie, the first transgenic cow produced human protein enriched milk, which contained the human alpha lactalbumin.
2. Alpha lactalbumin is a protein composed of 123 amino acidic and 4 disulphide bridges, with a molecular weight of 14178 Da.
3. In human milk, & lactalbumin is the most abundant protein comprising 25% of total protein found in human milk.
4. It is synthesized by the mammary glands & lactalbumin binds calcium and zinc ions and possesses bactericidal antitumor activities.