Of the four classes of biological molecules, the proteins are the most diverse in their functions. By some estimates, cells make more than 50,000 different proteins, with each protein having a specific job. With such diversity, what gives a protein its functionality and specificity? For proteins, form is function. In other words, the specific 3-dimensional shape of a protein is what allows it to do its job. Table 1 lists some of the major functions of proteins, but this list is not exhaustive. In fact, it is hard to think of any function in the body in which proteins are not integral.