Which enzyme initiates protein digestion in the stomach?

• A. Pepsin
• B. Amylase
• C. Lipase
• D. Trypsin

Answer: (A)

Protein digestion in the stomach begins with pepsin. It’s produced as pepsinogen by gastric chief cells and is activated by the acidic environment created by HCl from parietal cells. Once active, pepsin cleaves peptide bonds in proteins, starting their breakdown into smaller peptides. This activity is strongest in the stomach’s very acidic pH, around 1.5–2.0.

The other enzymes have different roles: amylase digests carbohydrates (primarily in the mouth and can have minor stomach activity), lipase digests fats (with gastric and pancreatic sources but most fat digestion occurs in the small intestine), and trypsin is a pancreatic protease that works in the small intestine after activation.