Digestion Of Proteins
Proteins are large molecules made up of strings of amino acids, which, for the most part, are composed of carbon (C), hydrogen (H), oxygen (O), and nitrogen (N). Amino acids are connected to one another by a chemical structure known as a peptide bond (Figure 2.3, Figure 2.4), in which the nitrogen on the left side of one amino acid joins to the carbon on the right side of the next amino acid. This creates a linear string of amino acids that then folds back on itself, forming very specific structures. A protein’s structure is important in determining its function. Proteins perform an enormous array of functions inside cells; virtually every type of protein performs a specific and different role in the organism. Proteins compose the cell’s skeleton and aid in molecular communication (within and between cells, and from one organ to another). Enzymes are also proteins; they promote chemical reactions inside and outside of cells.
One class of digestive enzyme, called a protease, digests proteins by cutting the peptide bond between adjacent amino acids. This frees amino acids from one another and allows them to be absorbed by the intestinal tract and re-used by the body. The liver can make most amino acids; however, the body cannot manufacture all amino acids, so it is necessary for people to acquire some of them from their diet. These are called essential amino acids. Proteases in the intestinal tract re-supply the body with essential amino acids, to replenish the supply depleted by the body’s various metabolic processes.