A Level Biology Practice Exam 2025 - Free A Level Biology Practice Questions and Study Guide

The function of pepsin in mammals is to digest proteins in the stomach. Pepsin is an enzyme that is secreted by the stomach lining as an inactive precursor called pepsinogen. When pepsinogen comes into contact with the acidic environment of the stomach, it is activated to pepsin. This enzyme then breaks down proteins into smaller peptides, which are essential for protein digestion. The acidic pH of the stomach is crucial for the activation of pepsin and for its enzymatic activity. This process is a vital part of the overall digestion, allowing proteins from food to be properly hydrolyzed into their building blocks, amino acids, that the body can then absorb and use for various biological functions.