When you eat food that contains protein or you ingest a dietary source of protein it does not immediately start building muscles and burning for energy. Protein has to be turned back into the amino acids that structured it in the first place. The process goes as follows; protein from food sources travels to the stomach where pepsin a digestive enzyme (also a protein) breaks the food protein back into polypeptide chains. Then the polypeptide chains continue down the digestive tract into the small intestine, where the polypeptide bonds are broken down even further into smaller peptide bonds by trypsin, and chymotrypsin proteolytic enzymes (also proteins). Next the peptide bonds are split into their individual amino acids by carboxypeptidase (brush border enzyme, also a protein), and are then absorbed by the Jejunum, the middle section of the small intestine. The amino acids are absorbed into the bloodstream and travel to the liver where their dispersal is regulated. Amino acids will be dispersed to cells during protein synthesis and will be sent to where they are most needed. This is what happens to proteins we eat, proteins from food are just a source of amino acids, units that will then structure new proteins made in our body.