Which enzyme is active in breaking down proteins in the stomach?

Pepsin is the enzyme that is specifically designed to break down proteins in the stomach. It is produced in an inactive form called pepsinogen by the gastric chief cells and is activated in the highly acidic environment of the stomach by hydrochloric acid. Once activated, pepsin catalyzes the hydrolysis of peptide bonds, which reduces proteins to smaller peptides and eventually amino acids, making the nutrients easier to absorb in subsequent stages of digestion.

The other options refer to different types of enzymes that work in various parts of the digestive system. Amylase is responsible for breaking down carbohydrates, primarily starches into sugars, and works in both the mouth and the small intestine. Lipase, on the other hand, breaks down fats into fatty acids and glycerol and is primarily active in the small intestine. Protease is a general term for any enzyme that breaks down proteins, but in the context of the stomach, pepsin is the specific protease that handles protein digestion.