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.