What is the key difference between pepsinogen and pepsin?

The key difference between pepsinogen and pepsin lies in their functional states. Pepsinogen is a zymogen, which means it is an inactive precursor to the enzyme pepsin. This inactive form is important because it prevents the premature digestion of proteins in the cells where it is produced, specifically in the stomach's gastric mucosa. Once pepsinogen is secreted into the acidic environment of the stomach, it is activated into pepsin, which is an active enzyme that facilitates protein digestion by breaking down peptide bonds.

This activation process is crucial in the digestive system, as it ensures that proteins are only broken down when they reach the stomach, where they need to be digested. Therefore, the understanding of pepsinogen as an inactive precursor and pepsin as an active enzyme is fundamental to human physiology and biochemistry, particularly regarding digestive enzyme regulation.