Structural biology is a branch of molecular biology that deals with the study of the structure, shape and function of biological macromolecules such as proteins, nucleic acids (DNA and RNA) and lipids. It involves techniques like X-ray crystallography, NMR spectroscopy, cryo-electron microscopy to determine the three dimensional structure of these molecules at atomic resolution. This information is crucial for understanding how biological systems work at a molecular level, which can help in developing new drugs and therapies targeting specific proteins or nucleic acids that are involved in diseases like cancer, viral infections etc.