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Question #46528
The Question
A vertebrate model is genetically engineered to express an insect midgut receptor to study the binding kinetics of the Bacillus thuringiensis (Bt) Cry toxin. A targeted mutation in the receptor's extracellular domain successfully prevents the activated Cry toxin from creating pores in the epithelial cells. However, the model subsequently develops severe organ-specific autoimmunity against its own intestinal lining. Which of the following best explains the molecular basis of this dual outcome?
Options
- A.
The mutation altered the receptor's conformational geometry, preventing toxin binding but generating a neo-antigenic determinant that disrupted self-tolerance.
- B.
The mutation caused the intestinal pH to become highly alkaline, which inhibited the solubilization of the protoxin while simultaneously denaturing self-antigens.
- C.
The inability of the activated toxin to bind caused it to act as an autoantibody, directly mediating the destruction of the intestinal epithelium.
- D.
The mutated receptor lost its differential permeability, allowing the inactive protoxin to enter the cell and trigger an intracellular autoimmune cascade.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Midgut_Epithelium|Alkaline_pH|Receptor_Specificity
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Integrating the structural specificity of receptor-ligand binding in both toxicology (Bt toxin) and immunology (self-tolerance).
The trap in Option B tests the student's precise recall of the Bt toxin activation sequence—many students see 'alkaline pH' and assume it is the correct answer without reading that it falsely claims alkaline pH 'inhibits' solubilization.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Human Health and Disease - Class 12 |
| Concept | Autoimmunity Principles |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |