Question

What were the challenges faced by scientists in producing biologically functional rat insulin?
i. Active insulin has two peptide chains A and B
ii. Natural insulin is secreted in the form of long chain proinsulin which has additional C peptide
iii. Sequence of rat insulin was not known to scientists
iv. Bacteria could not produce active insulin as gene was inserted in penicillinase gene

• A. i, ii and iv
• B. ii, iii and iv
• C. i, iii and iv
• D. iv and i

Answer 1

The correct option is A i, ii and iv

For cloning and producing active insulin scientists faced many challenges. Firstly, natural insulin is produced in the form of preproinsulin having N terminal A and B chains and a C peptide. The cDNA produced from mRNA of this preproinsulin has coding regions for all of them but the active insulin has only A and B chains bound by disulphide bonds. Secondly, the gene was inserted within the penicillinase gene and the resultant protein had proinsulin joint with penicillinase which made it biologically inactive. To overcome these problems scientist produced A and B chains in separate bacteria without C peptide as the sequence of each of these chains was well worked out and known to them and mixed the two products which formed biologically active insulin.