(a) Write the difference between the proinsulin and mature insulin.
(b) What are transgenic bacteria? Illustrate with an example.
(c) Why certain cotton plants are called Bt cotton?

OR

(a) Write the functions of cry IAc gene
(b) Write the functions of RNA interference (RNAi)
(c) State the consequence when Meloidogyne incognita consumes cells with RNAi gene.

(a) 

• Pro-insulin undergoes processing to form mature insulin. 
• Pro-insulin is made of three polypeptide chains A (21 amino acids), B (30 amino acids) and C (30 amino acids) whereas insulin consists of only A (21 amino acids) and B (30 amino acids) chains. These chains are bound by disulphide bridges.

(b) Bacteria have manipulated DNA having an extra (foreign) gene are known as transgenic bacteria, e.g. DNA sequences introduced in plasmid of E. coli to produce insulin chains.
(c) Bt cotton contains specific Bt toxin genes which were isolated from Bacillus thuringiensis and incorporated into certain cotton plants.

OR

(a) cry IAc codes for toxic insecticidal protein as inactive protoxins in Bacillus thuringinesis. Bt toxin kills the cotton bollworm.
(b) RNAi is short for “RNA interference” and it refers to a phenomenon where small pieces of RNA can shut down protein translation by binding to the messenger RNAs that code for those proteins. RNA interference is a natural process with a role in the regulation of protein synthesis and in immunity. RNAi takes place in all eukaryotic organisms as a method of cellular defense. 
(c) When Meloidogyne incognita ingested cells with RNAi, Processes that occur gene silencing of the specific mRNA occurs due to complementary dsRNA molecule formation that bind RNAi prevents translation of mRNA, thus causing death of the nematode.