Question

The first human hormone produced by recombinant DNA technology is
A) Insulin
B) Estrogen
C) Thyroxin
D) Progesterone

Answer 1

Hint: Recombinant DNA technology allows us to insert a gene of interest into the DNA of other species or through a vector, that can be transformed in a host system that can give multiple
copies of the DNA or gene of interest.

Complete answer: Insulin displays two features that facilitate its production by recombinant DNA techniques as the human protein is not modified after translation by the addition of sugar molecules so the bacteria can be the host cell for the recombinant insulin production. Insulin has two polypeptides, one of 21 amino acids (the A chain) and one of 30 amino acids (the B chain) which in humans they are synthesized as a precursor preproinsulin, which contains the A and B segments attached to a third chain (C) and along with a leader sequence which is removed after the translation, leaving the A and B polypeptides linked to each other by two disulfide bonds. Recombinant insulin can be produced byways like the synthesis of artificial genes for the A and B chains followed by the production of fusion proteins in E. coli. The procedure used was to synthesize trinucleotides representing all the possible codons and then join these together in the order by the amino acid sequences of both the chains so two recombinant plasmids were constructed. The artificial gene for the A chain, and the gene for the B chain where they were ligated to a lac z reading frame present in a pBR322-type vector so the insulin was expressed as fusion proteins, consisting of the first few amino acids of b-galactosidase followed by the A or B polypeptides and were separated by a methionine residue, so using cyanogen bromide the insulin polypeptides could be cleaved from the b-galactosidase. The purified A and B chains were then attached to each other by disulfide bond formation in the test tube and now all the segments are formed artificially by the prohormone codon.

Note: The insulin used in the earlier treatment of diabetes was originally obtained from the pancreas of pigs and cows so problems arise in its use to treat human diabetes due to minute change in its structure compared to human insulin and the difficult purification procedures.