Final answer:
Protein digestion starts in the stomach with the activation of pepsinogen to pepsin, which begins breaking down proteins into smaller polypeptides. The process continues in the small intestine with enzymes like trypsin and chymotrypsin, culminating in the absorption of amino acids.
Step-by-step explanation:
The digestion of proteins begins in the stomach with the activation of the zymogen pepsinogen. When pepsinogen comes into contact with hydrochloric acid (HCl) in the stomach, it is converted to its active form, pepsin. Pepsin then starts to break down proteins into smaller polypeptides. These smaller chains then travel to the small intestine where other enzymes, including trypsin and chymotrypsin, continue the chemical digestion by targeting specific bonds in the amino acid sequences, eventually reducing them to amino acids. These amino acids are then small enough to be absorbed into the bloodstream through the intestinal walls. This intricate process ensures that proteins are broken down effectively so the body can utilize their constituent amino acids for various physiological functions.