Protein molecules are vital for life. Not only do proteins form the building blocks of muscle, but they also play key roles in the storage of energy and the complicated ion flows that occur during neural activity. Many chemical reactions in the body are catalyzed by a class of proteins called enzymes, whilst communications within and between cells are all handled by proteins. One important goal of modern molecular biology is to design, from scratch, protein molecules that have a particular biological function. With this, and some general method of delivering proteins to a particular site in the body, many diseases for which there is currently no cure could be reduced to the level of nuisance caused by a sore throat. For this and other reasons, the properties and structures of proteins are being investigated by a variety of chemical and physical techniques.