Q.161 Zoology ⭐ 360° Option Elimination Active
NEET 2025 Zoology Question 161 Solution
Topic: Biotechnology and its Applications · Official NTA Booklet Code 45
Question
Why can't insulin be given orally to diabetic patients?
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Verified Against NTA Final Answer Key
Option (2) : It will be digested in Gastro-Intestinal (GI) tract
📚 Biotechnology and its Applications Easy
📋 Given Parameters & Problem Setup
Therapeutic Agent Insulin (polypeptide hormone used for diabetes mellitus)
Route Question Why insulin cannot be given orally
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⏱️ Save ~15 seconds The 30-Second Exam Hall Shortcut: ⚡ Peptide Hormone Route Fingerprint
Insulin is a PROTEIN! If swallowed orally, digestive proteases (pepsin in stomach, trypsin/chymotrypsin in intestine) will DIGEST it into inactive amino acids before it enters blood! It MUST be injected subcutaneously!
1 Analyze the biochemical nature of insulin:
2 - Insulin is a 51-amino acid polypeptide hormone consisting of chains A and B linked by disulfide bonds.
3 - The human gastro-intestinal (GI) tract is specialized to digest dietary proteins using potent endopeptidases and exopeptidases (pepsin, trypsin, chymotrypsin, carboxypeptidases).
4 - If taken orally, insulin is completely proteolyzed and inactivated in the stomach and duodenum.
5 - Therefore, it must be administered parenterally (subcutaneous injection) to reach circulation intact.
6 Direct answer: It will be digested in Gastro-Intestinal (GI) tract!
7 Select Option (2)!
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Why You Can 100% Trust This Shortcut: Gene Therapy for Adenosine Deaminase (ADA) Deficiency (NCERT Biology · Biotechnology and its Applications: Retroviral cDNA vector delivery).
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Step-by-Step Rigorous Workflow & Mathematical Proof
Step 1
Polypeptide Structure of Insulin
Human insulin is a small globular protein hormone synthesized by beta-cells of the pancreatic islets of Langerhans:
- • It comprises 51 amino acids distributed into two polypeptide chains: Chain A (21 residues) and Chain B (30 residues), cross-linked by two inter-chain disulfide bridges.
- • Its biological activity relies on an intact, three-dimensional folded conformation.
Step 2
Fate of Ingested Polypeptides in the Gastrointestinal Tract
The digestive physiology of orally consumed proteins:
- • In the stomach, gastric juice contains hydrochloric acid (pH ~1.8) and pepsin, which denatures and cleaves protein polypeptide bonds.
- • In the small intestine, pancreatic proteases (trypsin, chymotrypsin, elastase, carboxypeptidases) and intestinal brush-border peptidases rapidly hydrolyze insulin into dipeptides, tripeptides, and free amino acids.
- • As a consequence, intact functional insulin cannot survive transit through the GI tract to be absorbed into the portal circulation.
Step 3
Conclusion
Insulin cannot be administered orally because it undergoes enzymatic digestion in the gastrointestinal tract, matching Option (2).
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4-Option Deep Scan
360° Option Elimination Engine Key Feature
Diagnose every choice: Know exactly why the right option works and why distractors fail.
1 A
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Human recombinant insulin (Humulin) does not trigger immune attacks; the barrier is enzymatic digestion, not immunogenicity.
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Student Fallacy (Why candidates pick this trap): Confusing non-human antigenicity with oral degradation.
2 B
✓ 100% Correct Verdict & Scientific Reason:
100% correct. Protein hormones are degraded by gastric and pancreatic proteases upon oral ingestion.
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Why this is airtight: None; sound physiological and pharmacological reasoning.
3 C
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Structural variation between individuals does not prevent oral ingestion; proteolytic cleavage does.
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Student Fallacy (Why candidates pick this trap): Selecting a vague distraction.
4 D
✗ Incorrect Verdict & Scientific Reason:
Incorrect. Oral administration destroys insulin, reducing its oral bioavailability to near zero, not increasing it.
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Student Fallacy (Why candidates pick this trap): Reversing bioavailability terminology.
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NTA Trap Alert: Steroid vs Peptide Hormone Administration Routes
Steroid hormones (like estrogen, progesterone in birth control pills, or cortisone) can be taken ORALLY because they are lipids that resist gastric proteases. Protein/peptide hormones (insulin, glucagon, growth hormone) CANNOT be taken orally because proteases digest them!
🛡️ How to avoid the -1 mark: Steroid = Oral OK. Protein/Peptide = Digested by gut proteases!
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Core NEET Syllabus Standard
NEET Biology Core Syllabus · Biotechnology and its Applications / Chemical Coordination and Integration Standard Benchmark
Core Scientific Principle Tested:
"Insulin is a protein hormone that is enzymatically degraded by gastrointestinal proteases if taken orally."
Syllabus Focus: Genetically Engineered Insulin & Hormone Delivery
✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗
Insulin is a Protein -> Stomach Treats it like a Meal (Digested in GI tract)!
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