Biotechnology and Its Applications Question 3
3. What triggers activation of protoxin to active Bt toxin of Bacillus thuringiensis in boll worm?
(a) Body temperature
(b) Moist surface of midgut
(c) Alkaline $pH$ of gut
(d) Acidic $pH$ of stomach
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Answer : c
Hints & Solutions
(c) Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesises parasporal crystalline inclusions containing CryIA and CryIIAb proteins, some of which are toxic against a wide range of insect orders (for example, moth larva that attacks the fruiting bodies of certain crop), nematodes and human-cancer cells. These toxins are produced in inactive protoxins form but become activated when dissolve in the high alkaline $pH$ of insect gut. Once ingested by insects, these crystals are solubilised in the midgut, the toxins are then proteolytically activated by midgut proteases and bind to specific receptors located in the insect cell membrane, leading to cell disruption and insect death.
