Describe the chemical digestion of proteins, including the sites where it occurs, specific enzymes involved and their actions, the sources of the enzymes, and how certain enzymes are activated

Question

What will be an ideal response?

Answer 1

Protein digestion begins in the stomach, which secretes pepsinogen that is activated into the active enzyme pepsin by the action of hydrochloric acid. Pepsin breaks proteins into peptide fragments. In the small intestine, enzymes from the pancreas break down peptide fragments into smaller peptides and amino acids. The pancreas secretes three enzyme precursors: trypsinogen, chymotrypsinogen, and procarboxypeptidase, all of which enter the small intestine where they are activated and then break up proteins and peptide fragments. Trypsinogen is first activated by the enzyme enterokinase in the brush border of the small intestine. Trypsin then converts chymotrypsinogen to chymotrypsin and procarboxypeptidase to carboxypeptidase. The small intestine synthesizes aminopeptidases and embeds them within cell membranes of the brush border. These enzymes break peptide fragments into amino acids or very small peptides. The small intestine's epithelial cells absorb the amino acids and small peptides. The small peptides are then broken down to amino acids by intracellular peptidases.