Biophysics uses the tools of physics to watch biology in action. To visualize what macromolecules like proteins, RNA, or DNA look like, biophysicists use powerful X-rays or electron microscopes. These techniques can define the shape of the molecules. Most molecules need to be able to change between related shapes in order to functions. Mutations and drugs block these normal movements.
For example, mutations in proteins called kinases cause many types of cancer. These mutations cause the kinases to move aways from their inactive shape and become hyperactive. For some of these mutations, small molecule drugs can recognize these hyperactive shapes and inhibit them. A famous example is the interaction of the drug Gleevec with the kinase Abl. However because of the complexities of the different movements that proteins can make it remains a formidable challenge to design drugs that interact with great specificity.