Chemical digestion of proteins begins within the stomach. So within the stomach, we have specialized types of cells known as chief cells, that secrete a protein enzyme known as pepsin. And pepsin is responsible for cleaving chemical bonds on proteins. So within our stomach, the protein denatures as a result of the high acidity, and it also begins to break down. So pepsin breaks down the protein chemically into smaller units we call polypeptides. Now, those polypeptides will eventually reach the small intestine.