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The inactive form of Bt toxin is converted to the active form in the insect gut ___.
Insect Midgut = Alkaline pH (Solubilizes Crystals) -> Lytic Pores -> Death!
Bacillus thuringiensis produces intracellular protein crystals during sporulation containing toxic insecticidal Cry proteins. Because the crystals are insoluble at neutral/acidic pH, the protoxin remains non-toxic to the bacterium.
Susceptible insect larvae possess a strongly alkaline midgut environment (pH 9.0–10.5). Upon ingestion, the high alkaline pH solubilizes the crystal proteins into active monomers.
The activated toxin binds to cadherin receptors on the surface of midgut epithelial cells, inserting into the membrane to create open pores that cause osmotic swelling, cell lysis, gut paralysis, and death.
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100% accurate. Canonical physiological trigger that solubilizes crystalline Bt protoxin in insect midgut.
Incorrect. Acidic pH stabilizes the insoluble crystal and prevents activation (as in human stomach).
Incorrect. Proteases cannot digest or activate the crystal until it is first solubilized by the alkaline pH.
Incorrect. Nucleases digest nucleic acids (DNA/RNA); Cry toxin is a protein.
Medical students frequently associate digestion with acid (HCl in human stomach). Insect midguts are alkaline, which is why Bt toxin is lethal to bollworms but safe for humans.
"Inactive Bt protoxin is converted into active toxin due to the alkaline pH of the insect midgut which solubilises the crystals."
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