Protein Digestion
Exopeptidase
Cleaves bonds at the ends to release free amino acids.
Dipeptidase
Cleaves dipeptides
Endopeptidase
Cleaves peptide bonds within the chain to create smaller fragments.
Tripeptidase
Cleaves tripeptides
Hydrochloric acid
Converts the inactive form of the enzyme pepsinogen to its active form, pepsin.
Intestinal cells
Here, amino acids may be used for energy or to synthesize needed compounds.
Hydrochloric acid
Uncoils (denatures) each protein's tangled strands so that digestive enzymes can better attack the peptide bonds.
Peptidase
A digestive enzyme that hydrolyzes peptide bonds.
Pepsin
Initiates protein digestion by cleaving proteins- large polypeptides- into smaller polypeptides and some amino acids.
Peptidase enzymes
On the membrane surfaces of the intestinal cells, split most of the dipeptides and tripeptides into single amino acids. Only a few small peptides escape digestion and enter the blood intact.
Stomach
Partial breakdown (hydrolysis) of proteins.
Amino acid carriers
Transport amino acids into the intestinal cells.
Unused amino acids
Transported across the cell membrane into the surrounding fluid where they enter the capillaries on their way to the liver.
Small intestine
When polypeptides enter here, several pancreatic and intestinal proteases hydrolyze them further into short peptide chains, tripeptides, dipeptides, and individual amino acids.