Final answer:
The most important digestive enzyme in gastric juice is pepsin, which becomes active when food enters the stomach and the pH drops due to hydrochloric acid. Pepsin hydrolyzes protein peptide linkages, facilitating their breakdown into smaller molecules. Complete protein digestion occurs in the small intestine with the aid of pancreatic juices.
Step-by-step explanation:
The most important digestive enzyme in gastric juice is pepsin. Gastric juice, which is primarily composed of water, inorganic ions, hydrochloric acid (HCl), and various enzymes, plays a crucial role in protein digestion. HCl is first secreted by the parietal cells of the stomach lining and is responsible for creating a highly acidic environment with a pH ranging from 1.0 to 2.5. This acidity serves to denature food proteins, which is important for efficient enzyme action.
Pepsinogen, an inactive enzyme secreted by cells in the stomach wall, is converted into its active form, pepsin, when food enters the stomach. This transformation is triggered by the drop in pH when HCl is secreted. Pepsin then begins the process of breaking down proteins by hydrolyzing peptide linkages, specifically targeting linkages involving certain amino acids.
Although pepsin starts protein digestion, it is important to note that protein digestion is completed in the small intestine, where pancreatic juice plays a significant role. This juice, rich in various enzymes and bicarbonate, neutralizes the acidic chyme from the stomach and provides optimal conditions for the continued digestion of proteins and other macronutrients.