Which of the following digestive enzymes present in gastric juice is primarily responsible for breaking down proteins?

Appeared in: AIIMS Patna NO - 2020

Explanation

Pepsin is the principal proteolytic (protein-digesting) enzyme found in gastric juice within the stomach.
It is secreted by the chief cells of the stomach as an inactive zymogen called pepsinogen.
Hydrochloric acid (HCl) in the stomach creates a highly acidic environment (pH 1.5-2.5) which activates pepsinogen into its active form, pepsin.
Pepsin begins the complex process of protein digestion by breaking down large protein molecules into smaller fragments called proteoses and peptones.

Option A: Trypsin is not present in gastric juice; it is a pancreatic enzyme.
Option C: Peptidases are not the primary enzyme in gastric juice. They are found mainly in the small intestine.
Option D: Chymotrypsin, like trypsin, is a pancreatic enzyme that functions in the small intestine, not the stomach.

Clinical Relevance

Nursing practice connection: Knowing Physiology of Protein Digestion helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding the role of pepsin and gastric acid is crucial in managing conditions like Peptic Ulcer Disease (PUD) and Gastroesophageal Reflux Disease (GERD), where excess acid and pepsin can damage the mucosal lining.
Medications like Proton Pump Inhibitors (PPIs) and H2 blockers work by reducing gastric acid secretion. This not only relieves symptoms but also reduces the activation of pepsin, aiding in the healing of ulcers and esophageal tissue.
What if? If a patient has atrophic gastritis or is on long-term high-dose PPIs, they may have significantly reduced acid production (achlorhydria). This would impair protein digestion in the stomach because pepsinogen would not be effectively converted to active pepsin.

How to Approach the Question

First, identify the key phrases in the question stem: 'gastric juice' and 'breaking down proteins'.
Recall that 'gastric' refers to the stomach. The question is asking for the main protein-digesting enzyme in the stomach.
Systematically evaluate each option based on its primary site of action in the digestive system.
Remember that Pepsin is the classic enzyme associated with protein digestion in the stomach's acidic environment.
Eliminate Trypsin and Chymotrypsin, as they are secreted by the pancreas and act in the small intestine.
Eliminate Peptidases, as they are primarily involved in the final breakdown of peptides into amino acids in the small intestine.

Concept Tested & Keywords

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E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 1 (pp 26-370 of 370) p. 273-275

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 513-515

E6 Biochemistry U Satyanarayana— Part 1 (pp 26-420 of 840) p. 165-167

Practise the full AIIMS Patna NO - 2020

Attempt every question from this paper in a timed mock, then review the full solution for each one.