In human body, the digestion of protein begins in which of the following organs ?

Question

UnlockIAS · Accepted Answer

Correct — D, the stomach. Protein digestion begins in the stomach. Gastric glands secrete hydrochloric acid, which activates the inactive enzyme pepsinogen into pepsin; pepsin, working in the acidic medium, breaks proteins down into smaller peptides. No protein-digesting enzyme acts earlier in the tract — saliva in the mouth has no protease. Protein digestion is then completed in the small intestine (by pancreatic trypsin/chymotrypsin and intestinal peptidases), but it BEGINS in the stomach.

Why the other options are wrong — (a) The liver secretes bile, which emulsifies fats — it has no role in starting protein digestion and secretes no protein-digesting enzyme.  (b) In the mouth, saliva contains ptyalin (salivary amylase), which begins the digestion of starch (carbohydrate), not protein — there is no protease in saliva.  (c) The small intestine COMPLETES protein digestion (trypsin, chymotrypsin, peptidases) but does not begin it — digestion of protein has already started in the stomach with pepsin.

Concept: Digestion of the three macronutrients begins in different places. Carbohydrate (starch) digestion begins in the mouth (salivary amylase/ptyalin). Protein digestion begins in the stomach, where HCl converts pepsinogen to pepsin and pepsin breaks proteins into peptides. Fat digestion mainly occurs in the small intestine (bile emulsifies, pancreatic lipase digests). The small intestine is where all three are finally completed and absorbed.

State PCS 2020 Q95 — Science & Technology PYQ with Answer

State PCS 2020 Q95 — Science & Technology PYQ with Answer