Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
Which one of the following is an example of a neurotoxin?
Options:
(A) Cholera toxin
(B) Streptolysin-O
(C) Botulinum toxin
(D) Diphtheria toxin
Official Answer Key:
C
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2018 Q.15)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Microbiology & Toxicology (Bacterial Toxins & Neurotoxins)
**2. Detailed Step-by-Step Analysis**:
- A **neurotoxin** is a poisonous substance that specifically disrupts the structure or electrical/chemical signaling functions of the nervous system.
- **Botulinum toxin** (produced by the anaerobic bacterium *Clostridium botulinum*) is an extremely potent neurotoxin. It enters cholinergic presynaptic nerve terminals and functions as a zinc-dependent endopeptidase that proteolytically cleaves SNARE proteins (SNAP-25, syntaxin, or synaptobrevin/VAMP), thereby preventing acetylcholine release at neuromuscular junctions and causing flaccid paralysis.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: *Cholera toxin* (produced by *Vibrio cholerae*) is an enterotoxin that ADP-ribosylates the $G_{lpha s}$ protein, causing constitutive adenylate cyclase activation and severe secretory diarrhea.
- **Option (B) [INCORRECT]**: *Diphtheria toxin* (produced by *Corynebacterium diphtheriae*) is a cytotoxin that ADP-ribosylates eukaryotic elongation factor 2 (eEF-2), halting protein translation.
- **Option (C) [CORRECT]**: *Botulinum toxin* is a classical neurotoxin blocking neuromuscular neurotransmission.
- **Option (D) [INCORRECT]**: *Lipopolysaccharide (LPS)* is an endotoxin found in the outer membrane of Gram-negative bacteria that triggers systemic inflammatory and pyrogenic immune cascades via TLR4.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **C**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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