Final answer:
Hydrochloric acid (HCl) in the stomach converts pepsinogen into its active enzyme form, pepsin, which plays an essential role in protein digestion by breaking down peptide bonds.
Step-by-step explanation:
Hydrochloric acid (HCl) plays a vital role in digestion within the stomach by converting pepsinogen to its active form, pepsin. Pepsinogen is an inactive enzyme produced by the chief cells in the gastric glands. When food is ingested, it stimulates the secretion of HCl by the parietal cells in the stomach lining. The acidic environment (pH between 1.5 and 2.5) created by HCl unfolds proteins and converts pepsinogen into pepsin. Pepsin is a proteolytic enzyme, meaning it helps in the digestion of proteins by breaking down peptide bonds, particularly targeting aromatic amino acids like tryptophan, tyrosine, and phenylalanine.
This conversion process is also known as autocatalysis. Once activated, pepsin assists in breaking down dietary proteins into smaller peptides and eventually into amino acids, which can then be absorbed by the body. Contrary to its role in digestion, HCl also has an antiseptic function, killing most of the bacteria and other microorganisms present in food.