Correct Option
The correct option is Pepsin.
Explanation
Digestion involves the biochemical breakdown of complex food macromolecules into simpler, absorbable forms. Protein digestion specifically commences in the stomach, which provides a highly acidic environment essential for the activation and function of specific gastric enzymes.
Option Analysis
- Pepsin is correct: Pepsin is the principal proteolytic enzyme found in the stomach. It is secreted by the peptic (chief) cells of the gastric glands in an inactive form called pepsinogen. Upon exposure to Hydrochloric Acid (HCl), which maintains a pH of approximately 1.8 in the stomach, pepsinogen is converted into the active enzyme pepsin. Pepsin initiates protein digestion by converting proteins into proteoses and peptones.
- Trypsin is incorrect: Trypsin is a proteolytic enzyme secreted by the pancreas into the small intestine (duodenum). Unlike pepsin, trypsin requires an alkaline medium (pH 7.1-8.2) to function effectively.
- Amylase is incorrect: Amylase is primarily involved in carbohydrate digestion. Salivary amylase (ptyalin) acts in the mouth, and pancreatic amylase acts in the small intestine to break down starch. It does not digest proteins.
- Lipase is incorrect: Lipase is the enzyme responsible for the hydrolysis of fats (lipids). While gastric lipase is present in the stomach in small quantities, it plays a minor role compared to pancreatic lipase in the small intestine, and it does not digest proteins.
Key Takeaway
Pepsin is the primary enzyme responsible for initiating protein digestion in the acidic environment of the stomach, whereas Trypsin continues protein digestion in the alkaline environment of the small intestine.