What happens to the activity of pepsin when it enters the small intestine where the pH is 8
The Correct Answer and Explanation is:
Pepsin is an enzyme that is most active in the acidic environment of the stomach, where the pH typically ranges from 1.5 to 3.5. When pepsin enters the small intestine, however, the pH increases significantly and becomes much more alkaline, usually ranging from 6 to 8.
Pepsin, which is initially secreted in its inactive form (pepsinogen), is activated in the acidic conditions of the stomach. It functions optimally in the acidic environment by breaking down proteins into smaller peptides. However, once it moves into the small intestine, the alkaline pH conditions reduce its activity significantly.
The reason for this drop in activity is that enzymes are highly sensitive to pH levels. Each enzyme, including pepsin, has an optimal pH range within which its structure is maintained, and it can function most effectively. When the pH moves away from this optimal range, the enzyme’s active site can change shape (denaturation), and the enzyme’s ability to bind and catalyze reactions decreases.
In the small intestine, the pH is raised by the secretion of bicarbonate from the pancreas and bile from the liver. These substances neutralize the stomach acid and create a more suitable environment for enzymes that function at neutral or slightly alkaline pH, such as trypsin, an enzyme from the pancreas that further breaks down proteins.
Therefore, pepsin’s activity diminishes as it enters the small intestine, and its role is largely taken over by other digestive enzymes more suited to the neutral-to-alkaline pH of the small intestine. This shift ensures the digestive process continues efficiently in both the stomach and small intestine.
