# The Digestion of Proteins --- The [[digestion]] of [[protein]] is the breakdown of proteins by [[protease|proteases]] into their individual [[amino acids]]. Once done, [[enterocytes]] in the intestines absorb them into the bloodstream. Proteases are highly specific. They either target specific peptide bonds between specific amino acids (for example, **trypsin** cleaves the bond between arginine and lysine, and **chymotrypsin** breaks the bond at hydrophobic amino acids), if they're next to each other, or any amino acid as long as it's at the end of the peptide chain. ![[protein digestion.png]] ## Mouth Very little of protein digestion actually occurs in the [[mouth]]. There is a some large scale breakdown due to [[digestion#Mechanical and Chemical Digestion|mechanical digestion]] (i.e. chewing), but proteins generally hit the stomach whole. ## Stomach The [[stomach]] produces two important substances for the breakdown of proteins: [[stomach acid]] and [[protease]]. **HCl** is produced by the [[gastric gland#Parietal Cells|parietal cells]] of the gastric glands in response to the hormone [[gastric gland#G Cells|gastrin]]. This does two important things to proteins in the stomach: one is *denaturing* the protein, which is breaking the bonds of the [[protein structure|quaternary]], [[protein structure|tertiary]] and [[protein structure|secondary]] protein structures, and secondly it activates the *[[protease|pepsin]]* from it's initial form, *pepsinogen* **Pepsin** breaks the [[protein structure|primary structure]] of the protein into shorter polypeptides. ## Small Intestine Once in the [[small intestine]], trypsin and other proteases from the [[pancreas]] break down the polypeptides into single amino acids, dipeptides or tripeptides. From there they are [[nutrient absorption#Absorption of Amino Acids|absorbed]] into the bloodstream. ___