Final answer:
Protein digestion starts in the stomach with the help of gastric juices containing hydrochloric acid and pepsin, breaking proteins into smaller chains for further digestion and absorption in the small intestine.
Step-by-step explanation:
Protein digestion begins in the stomach with the action of gastric juices, primarily hydrochloric acid (HCl) and the enzyme pepsin. Gastric juice, a complex mixture of water, inorganic ions, enzymes, and other proteins, assists in breaking down proteins into smaller polypeptides.
HCl plays a critical role in unfolding proteins (denaturation), thus enabling more efficient enzyme action, while pepsin, secreted as an inactive precursor (pepsinogen), is activated in the acidic environment to catalyze the hydrolysis of peptide bonds, particularly those involving aromatic amino acids. This process not only digests proteins but also kills many microorganisms ingested with food.
Protein digestion is a multi-step process that involves the initial hydrolysis of about 10% of peptide bonds in the stomach. The production of chyme—a mixture of partially digested food and gastric juice—marks the continuation of digestion as it moves into the small intestine under the regulation of the pyloric sphincter. In the small intestine, other enzymes including trypsin and chymotrypsin further break down proteins, ultimately leading to the absorption of amino acids.
Overall, the digestion of proteins is essential for the absorption of essential amino acids, which must be obtained through diet as they cannot be synthesized by the human body.