What happens to the protein molecules in food, from the time it is swallowed, to the time its products are built up in the cytoplasm of a muscle cell.

Explanation

Proteins and partially digested proteins in the chyme on reaching the intestine are acted upon by the proteolytic enzymes of pancreatic juice. Trypsin hydrolyses proteins into polypeptides and peptones, while chymotrypsin hydrolyses peptide bonds associated with specific amino acids .
Proteins are source of amino acids required for growth and repair of body cells. They are stored in the body only to a certain extent, large quantities are excreted as nitrogenous waste.