The methyl side chain of serine contains a hydroxy group making this one of two amino acids that are also alcohols. Serine plays a major role in a variety of biosynthetic pathways including those involving pyrimidines, purines, creatine, and porphyrins. Serine is also found at the active site in an important class of enzymes termed "serine proteases" that include trypsin and chymotrypsin. These enzymes catalyze the hydrolysis of peptide bonds in polypeptides and proteins, a major function in the digestive process. On a molar basis, serine is incorporated into proteins at a rate of 7.1 percent compared to the other amino acids.