Tireless workers in the cell, proteins function as tiny molecular machines. Like other machines, proteins are tightly designed to perform specific jobs, which, like any widget, depend entirely on its precise shape. A wrong measurement can shut the entire cellular--or even bodily--system down. To do their jobs, protein chains constantly wiggle, twist and fold to properly hook up with other functional molecules. Researchers are examining protein structures to learn more about how they function. Others aim to predict how a single string of building blocks turns into the vital 3-D shape proteins need to work properly. NSF-supported scientists are actively developing computer programs to accomplish this difficult task.