UPPSC 2025 Prelims GS Paper-I · Question 30 of 150

Correct — C, Only 3, that is pepsin alone. Of the three proteases listed, only pepsin is actually released into the stomach. The chief cells of the gastric glands secrete it in an inactive form, pepsinogen; the hydrochloric acid poured out by the neighbouring parietal cells drops the gastric pH to roughly 1.5-2 and clips pepsinogen into active pepsin, after which pepsin itself activates more pepsinogen. Pepsin is an endopeptidase: it cuts the interior peptide bonds of a protein and yields shorter chains — proteoses and peptones — rather than free amino acids. Trypsin and chymotrypsin are not gastric at all. Both are made by the acinar cells of the PANCREAS, travel down the pancreatic duct as trypsinogen and chymotrypsinogen, and are switched on in the DUODENUM: enteropeptidase (enterokinase) from the duodenal lining activates trypsin, and trypsin then activates chymotrypsin. So protein digestion begins in the stomach with pepsin and is completed in the small intestine by the pancreatic proteases.

• (a)Only 1 and 2 — This picks the two enzymes that are definitely NOT gastric — chymotrypsin and trypsin are both pancreatic zymogens activated in the duodenum — and simultaneously drops pepsin, the one enzyme the stomach really does release. It is wrong on all three counts.
• (b)Only 2 and 3 — Pepsin belongs, but trypsin does not. Trypsin is secreted by the pancreas as trypsinogen and is activated by enteropeptidase in the duodenum; it also needs the alkaline conditions of the small intestine, and would be useless in the stomach's acid. Adding one wrong name to the right one still loses the mark.
• (d)1, 2 and 3 — The 'all of the above' trap, and the commonest wrong answer here. All three are genuine protein-digesting enzymes, so a candidate who only checks 'does it digest protein?' ticks everything. The question asks something narrower — where the enzyme is RELEASED — and on that test two of the three fail.

Protein digestion is a two-stage, two-organ process. In the stomach, an intensely acidic medium and pepsin begin the job by breaking long protein chains into shorter polypeptides. In the small intestine, alkaline pancreatic juice neutralises the acid chyme and delivers trypsin, chymotrypsin and carboxypeptidase, which finish the work; the brush-border peptidases of the intestinal wall release the final amino acids for absorption. Every one of these proteases is secreted as an inactive precursor — a zymogen — and is activated only after it has left the gland, which is how the pancreas and the stomach lining avoid digesting themselves.

The question separates the site where an enzyme is PRODUCED and RELEASED from the general fact that it digests protein. A quick way to sort the three is by the pH each one needs: pepsin works only in strong acid, around pH 1.5-2, which exists nowhere in the body except the stomach; trypsin and chymotrypsin work near pH 8, the alkaline range that bicarbonate-rich pancreatic juice creates in the duodenum. An enzyme that needs alkali cannot be a stomach enzyme. The temptation is option (d), because all three names are familiar from the same chapter and all three genuinely attack protein.

• Pepsin is secreted by the chief (peptic) cells of the gastric glands as pepsinogen, and is activated by the hydrochloric acid released by the parietal (oxyntic) cells
• Trypsin and chymotrypsin are pancreatic: secreted as trypsinogen and chymotrypsinogen, activated in the duodenum by enteropeptidase (enterokinase) and by trypsin respectively
• Pepsin needs a strongly acidic medium (about pH 1.5-2); the pancreatic proteases need the alkaline medium (about pH 8) produced by bicarbonate in pancreatic juice
• Proteases are secreted as inactive zymogens precisely so that they cannot digest the gland that makes them; activation happens in the lumen
• Other gastric secretions include hydrochloric acid, gastric lipase, intrinsic factor, mucus, and rennin (chymosin) in infants — while gastrin is a hormone, not an enzyme

• Marking 'all three' because every name listed is a genuine protein-digesting enzyme — the question asks where each is released, not what it does
• Confusing the site where an enzyme is produced with the site where it acts; pancreatic enzymes are the standard exception, made in one organ and active in another
• Treating gastrin as a gastric enzyme — it is a hormone that stimulates acid and pepsinogen secretion

UPPSC keeps this factual and organ-based — which enzyme, which organ, which begins where — while UPSC prefers the assertion-reason or process form, testing whether you know that digestion of protein starts in the stomach but is finished in the small intestine.

• practice — not a real PYQ

  Trypsinogen present in pancreatic juice is converted into active trypsin by

  • (a)hydrochloric acid of the stomach
  • (b)enteropeptidase (enterokinase) secreted by the duodenal mucosa
  • (c)bile salts released from the gall bladder
  • (d)pepsin carried down from the stomach

  Answer(b) enteropeptidase (enterokinase) secreted by the duodenal mucosa — the activated trypsin then goes on to activate chymotrypsinogen and the other pancreatic zymogens.

• practice — not a real PYQ

  Which of the following is secreted by the parietal (oxyntic) cells of the gastric glands?

  • (a)Pepsinogen
  • (b)Mucus
  • (c)Hydrochloric acid and intrinsic factor
  • (d)Gastrin

  Answer(c) Hydrochloric acid and intrinsic factor — pepsinogen comes from the chief cells, mucus from the mucous neck cells, and gastrin is a hormone from the G cells.