What is the role of stomach acid?
HCl (hydrochloric acid) aids in chemical digestion in the stomach.
Most proteins begin digestion in the stomach. Cells of the stomach secrete the inactive zymogen pepsinogen, which is an enzyme that is activated by HCl. In its active form, pepsinogen is called pepsin. Pepsin breaks the peptide bonds that link amino acids.
Thus, HCl is involved in chemical digestion of proteins in the stomach.