Which enzyme initiates protein digestion and where is it produced?

• A. Amylase, produced in the salivary glands
• B. Pepsin, produced in the stomach
• C. Trypsin, produced in the pancreas
• D. Lactase, produced in the small intestine

Answer: (B)

Protein digestion starts in the stomach with an enzyme that cleaves peptide bonds in proteins. This enzyme is pepsin, which is secreted in its inactive form pepsinogen by stomach cells and is activated by the highly acidic environment created by hydrochloric acid in the stomach. That acidic setting is essential for pepsin’s activity, letting it begin breaking down proteins early in the digestive process. The other enzymes listed target different nutrients or act later in digestion: amylase digests carbohydrates and comes from the salivary glands (and the pancreas), lactase digests lactose in the small intestine, and trypsin—produced by the pancreas as trypsinogen and activated in the small intestine—continues protein digestion after pepsin, but does not initiate it.