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 an additional C peptide
iii. The sequence of rat insulin was not known to scientists
iv. Bacteria could not produce active insulin as the insulin gene was inserted in the 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 an N terminal, A and B chains, and a C peptide. The cDNA produced from the 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 insulin gene was inserted within the penicillinase gene and the resultant protein had proinsulin joined with penicillinase which made it biologically inactive. To overcome these problems scientists produced A and B chains in separate bacterial cultures without C peptide as the sequence of each of these chains was well known to them. They then mixed the two products to form biologically active insulin.