Read the following paragraph and answer the given questions.
RNAi takes place in all eukaryotic organisms as a method of cellular defense. The source of this complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate. Insulin from an animal source, though caused some patients to develop allergy or other types of reactions to the foreign protein. Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges. Transgenic mice are being developed for use in testing the safety of vaccines before they are used on humans. Transgenic mice are being used to test the safety of the polio vaccine. If successful and found to be reliable, they could replace the use of monkeys to test the safety of batches of the vaccine. Specific Bt toxin genes were isolated from Bacillus thuringiensis and incorporated into the several crop plants such as cotton. The choice of genes depends upon the crop and the targeted pest, as most Bt toxins are insect-group specific. The toxin is coded by a gene cryIAc named cry. There are a number of them, for example, the proteins encoded by the genes cryIAc and cryIIAb control the cotton bollworms, that of cryIAb controls corn borer.
Which of these is not present in mature insulin?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → C peptide
The passage says insulin has two short polypeptide chains, A and B, linked by disulphide bridges. In the body, insulin is first made as a pro-hormone, pro-insulin, which has an extra stretch called the C peptide. The C peptide is cut out when pro-insulin matures into insulin.
Option (1) Disulfide bonds — Present in mature insulin.
Option (2) C peptide — Not present in mature insulin. Pro-insulin has three parts, the A and B chains and the extra C peptide. The C peptide is cut out during maturation, so mature insulin keeps only chains A and B joined by disulphide bridges.
Option (3) A peptide — Present in mature insulin.
Option (4) B peptide — Present in mature insulin.
Note: The passage is taken from NCERT. NTA has put lines of the NCERT text together to make it. Most CUET (UG) questions come straight from NCERT, so study the book line by line, including figures and their titles.
NCERT Extract:
Genetically Engineered Insulin – “… In mammals, including humans, insulin is synthesised as a pro-hormone (like a pro-enzyme, the pro-hormone also needs to be processed before it becomes a fully mature and functional hormone) which contains an extra stretch called the C peptide. This C peptide is not present in the mature insulin and is removed during maturation into insulin.”
Genetically Engineered Insulin – “… Insulin consists of two short polypeptide chains: chain A and chain B, that are linked together by disulphide bridges (Figure 10.3).”