What specifically initiates protein digestion?

• A. Saliva
• B. Stomach acid
• C. Intestinal enzymes
• D. Gastric enzymes

Answer: (D)

Protein digestion begins in the stomach, where gastric enzymes play a crucial role. The primary gastric enzyme involved is pepsin, which is secreted as an inactive precursor called pepsinogen. When pepsinogen comes into contact with the hydrochloric acid produced by the stomach, it is converted into its active form, pepsin. This active enzyme breaks down proteins into smaller peptides, marking the first step in the digestion of proteins.

Stomach acid, while important, primarily serves to activate these enzymes and create an acidic environment optimal for their action. Saliva contains an enzyme called salivary amylase, which is responsible for carbohydrate digestion rather than proteins. Intestinal enzymes, such as those produced by the pancreas or lining of the small intestine, further digest proteins into amino acids, but this process occurs after initial digestion has started in the stomach. Therefore, gastric enzymes are specifically responsible for initiating the digestion of proteins in the digestive process.