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(d) C-peptide is not present in the mature insulin $nd is removed during maturationinto
insulin. Thus, the main challenge for the production of insulin using rDNA techniques was
getting insulin assembled into a mature form.
(e) Eli Lilly an American company in 1983, prepared two DNA sequences corresponding to A
and B-chains of human insulin and introduced them in plasmids of E. coli to produce insulin
chains. Chains-A and B were produced separately, extracted and combined by creating
disulphide bonds to form human insulin.
II. Production of vaccines through genetic engineering such vaccines are called
recombinant vaccines also called ‘subunit vaccines’ or ‘second generation vaccines’, e.g
hepatitis-B. These are of two types:
(a) Protein vaccines use of specific protein produced by rDNA in vaccine.
(b) DNA vaccines use of genetically engineered DNA to be injected as vaccine to produce an
immunological response.
Hepatitis vaccine contains the viral envelope protein, hepatitis-B surface antigen (HB8 Ag).
This gene is isolated from yeast vectors.
Some protein coding genes isolated from pathogens are also incorporated and expressed in
plants produce antigens and are also called edible vaccines.
III. Gene therapy is a collection of methods that allows correction of gene defects,
diagnosed in a child or embryo.
(a) Genes are inserted into a person’s cells and tissues to treat a disease.
(b) Correction of a genetic defect involves delivery of a normal gene into the individual or
embryo to take over the function and compensate for the non-functional gene.
(c) First gene therapy was given to a four year old girl with Adenosine Deaminase (ADA)
deficiency by M Blease and WF Andresco in 1990s.
• ADA is caused due to the deletion of the gene for adenosine deaminase.
• In some children, ADA deficiency can be cured by bone marrow transplantation and
enzyme replacement therapy, but they are not completely curable.
(d) Steps involved are as follows: